1 General Technique, Anatomy, and Basic Interpretation

The cervical spine connects the skull to the trunk; it articulates with the occiput above and the thoracic vertebrae below. The bony elements, muscles, ligaments, and intervertebral discs support and provide protection to the spinal cord. On plain films, one can appreciate the bony morphology of the vertebrae and the disc spaces and assess the alignment of the vertebral column very quickly. This indirectly provides information regarding the integrity of the ligaments, which are crucial in maintaining alignment of the cervical spine. However, individual ligaments and muscle groups all have the same or similar attenuation and cannot be differentiated from one another on plain film. A systematic approach is recommended to evaluate the spine for bony integrity, alignment, cartilage, joint space, and soft tissue abnormalities. The disadvantages of cervical spine radiography are the limited range of tissue attenuation and the loss of spatial resolution caused by overlapping bone structures.

The most common indications for obtaining cervical spine radiographs in today’s medical practice are for the evaluation of trauma, spinal stability, and cervical spondylosis and in the search for radiopaque foreign bodies. Different views of the cervical spine are tailored to each clinical need. The most common views are the lateral, anteroposterior (AP), open-mouth odontoid, oblique, and pillar views (Fig. 2-1). In acute cervical spine injury, cross-table lateral, AP, and open-mouth odontoid views are recommended. A lateral view reveals the majority of injuries (Fig. 2-2); however, patients who are rendered quadriplegic by severe ligamentous injuries may demonstrate a normal lateral cervical spine radiograph. When the AP and then the open-mouth odontoid views are added to the cross-table lateral view of the cervical spine, the sensitivity of detecting significant injury is increased from 74% to 82% and then to 93%.¹⁰ In today’s practice, cross-sectional imaging (i.e., CT of the spine) has become a mainstay in the evaluation of the cervical spine, especially in the setting of acute trauma. MRI is particularly useful in evaluating the spinal cord.

Figure 2-1 Normal cervical spine series. A, Lateral view shows upper (a) and lower (b) end plates of the third cervical vertebra (C3), transverse process (c), pedicle (d), facet joint (e), articulating facets (f), posterior spinous process (g), posterior arch of C1 (h), anterior arch of C1 (i), atlantoaxial distance (j), and hyoid bone (k). B, Anteroposterior view shows smoothly undulating cortical margins of the lateral masses (a), joint of Luschka (b), superior (c) and inferior (d) end plates, and a midline posterior spinous process (e). C, Open-mouth odontoid view shows the odontoid tip (a), centered between the lateral masses of the axis; symmetrical lateral margins of the lateral atlantoaxial joints (b); and a spinous process (c). D, Oblique view shows laminae of the articular masses (a), reflecting the shingling effect, and an intervertebral (neural) foramen (b).

Figure 2-2 Cervical spine fracture. Lateral radiograph of the cervical spine demonstrates a compression fracture of the C5 vertebra (arrow). A retropulsed fragment impinges on the spinal canal.

In brief, a normal lateral cervical radiograph should demonstrate seven intact vertebrae and normal alignment of the anterior and posterior aspects of the vertebral bodies. This is especially important for trauma victims, because 7% to 14% of fractures are known to occur at the C7 or C7-T1 level.¹¹ The posterior vertebral body line is more reliable and must be intact. The anterior vertebral line is often encumbered by the presence of anterior osteophytes. Normal facet joints overlap in an orderly fashion, similar to shingles on a rooftop. The spinolaminar line, which is the dense cortical line representing the junction of the posterior laminae and the posterior spinous process, is uninterrupted. Relative uniformity of the interlaminar (interspinous) distances should be observed. The posterior spinal line (i.e., posterior cervical line), an imaginary line extending from the spinolaminar line of the atlas to C3 (Fig. 2-3), should demonstrate a continuous curve in parallel to the posterior vertebral body line; the distance between the two correlates with the spinal canal diameter.¹²

Figure 2-3 Normal lateral cervical spine radiograph (A) demonstrates normal alignment. a, Anterior spinal line; b, posterior vertebral line; c, posterior spinal line. B, Lateral scout view of a computed tomography scan demonstrates anterior subluxation of C4 on C5.

The anatomy and integrity of the craniocervical junction are crucial to the anesthesiologist. To achieve successful and safe endotracheal intubation, the anterior atlantodental interval (AADI), the vertical and anterior-posterior position of the dens, and the degree of extension of the head on the neck must be considered. The anterior arch of C1 bears a constant relationship to the dens; this is the AADI or predental space. It is defined as the space between the posterior surface of the anterior arch of C1 and the anterior surface of the dens. In flexion, because of the physiologic laxity of the cervicocranial ligaments, the anterior tubercle of the atlas assumes a more normal-appearing relationship to the dens, and the AADI increases in width, greater rostrally than caudally. In children and with flexion in adults, the AADI is normally about 5 mm. In adults, it is generally accepted that the AADI is 3 mm or less (Fig. 2-4).¹²

Figure 2-4 Anterior atlantodental interval (AADI). A, Lateral radiograph of the cervical spine in an adult patient. The AADI or predental space (arrows) is normally less than 3 mm. B, Lateral radiograph of the cervical spine in a pediatric patient. An AADI of up to 5 mm (curved arrow) can be normal in a child. The basion, the midpoint of the anterior border of the foramen magnum, is indicated by the straight arrow. The dotted line is an imaginary line indicating the inferior extension from the basion, and the posterior axial line is indicated by the solid line. The distance between the dotted line and the solid line is the basion-axial interval (BAI); it should be 12 mm or less for a normal occipitovertebral relationship in a child.

The bony structures of the atlantoaxial joint provide mobility (e.g., rotational movement) rather than stability. Therefore, the ligaments play a significant role in stability. The most important ligaments in the upper cervical spine are the transverse ligament, the alar ligaments, and the tectorial membrane. If the transverse ligament is disrupted and the alar and apical ligaments remain intact, up to 5 mm of movement at the atlantoaxial joint can be seen.¹³ If all the ligaments have been disrupted, the AADI can measure 10 mm or larger. In atlantoaxial subluxation, the dens is invariably displaced posteriorly, which causes narrowing of the spinal canal and potential impingement of the spinal cord. The space available for the spinal cord is defined as the diameter of the spinal canal as measured in the AP plane, at the C1 level, that is not occupied by the odontoid process. In the normal spine, this space is approximately 20 mm.¹³

2 Pertinent Findings and Pathology

a Pseudosubluxation and Pseudodislocation

Pseudosubluxation and pseudodislocation are terms applied to the physiologic anterior displacement of C2 on C3 that is frequently seen in infants and young children (Fig. 2-5). Physiologic anterior displacement of C2 on C3 and of C3 on C4 occurs in 24% and 14%, respectively, of children up to 8 years of age.¹⁴

Figure 2-5 Pseudosubluxation at C2-C3. T2-weighted sagittal magnetic resonance cervical spine study demonstrates physiologic anterior displacement of C2 on C3 in a child. Also seen are normal soft tissue masses encroaching on the airway from adenoids (a), palatine tonsils (b), and lingual tonsils at the base of the tongue (c).

In pediatric trauma cases, if C2 is anteriorly displaced and there are no other signs of trauma such as posterior arch fracture or prevertebral soft tissue hematoma, the spinolaminar lines of C1 through C3 should have a normal anatomic relationship. In a neutral position, the spinolaminar line of C2 lies on or up to 1 mm anterior or posterior to the imaginary posterior spinal line. If the C2 vertebra is intact, as the C2 body glides forward with respect to C3 during flexion, the spinolaminar line of C2 moves 1 to 2 mm anterior to the posterior spinal line. Similarly, with extension, the posterior translation of the C2 body is mirrored by similar posterior displacement of the spinolaminar line of C2 with respect to the posterior spinal line.

In traumatic spondylolisthesis, which is rare in children but more common in adults, the C2 body would translate anteriorly in flexion and posteriorly in extension, and the posterior spinal line would be maintained because of intact ligaments. However, flexion and extension films are not advisable if traumatic spondylolisthesis is suspected.

b Congenital and Developmental Anomalies

Occipital Fusion of C1

Important to rigid laryngoscopy and endotracheal intubation is the distance between the occiput and the posterior tubercle of C1, known as the atlanto-occipital distance (Fig. 2-6), which is quite variable from individual to individual. Head extension is limited by the abutment of the occiput to the posterior tubercle of C1. It has been proposed that a shorter atlanto-occipital distance decreases the effectiveness of head extension and contributes to difficult intubation.^13,15 Occipitalization of C1 with the occiput (atlanto-occipital fusion) not only limits head extension but also adds stress to the atlantoaxial joint. Although the majority of head extension occurs at the atlanto-occipital joint, some extension can also occur at C1-C2.¹⁵ Nichol and Zuck observed that in patients with limited or no extension possible at the atlanto-occipital joint, general extension of the head actually brings the larynx “anterior,” thus limiting the visibility of the larynx on laryngoscopy.¹⁵

Figure 2-6 Atlanto-occipital distance. A, Lateral radiograph of the cervical spine in neutral position; the arrow indicates the atlanto-occipital distance. B, Lateral radiograph of the cervical spine in hyperextension. Head extension is limited by the abutment of the occiput to the posterior tubercle of C1.

Nonfusion of Anterior and Posterior Arches Of C1

Ossification of the atlas begins with the lateral masses during intrauterine life. At birth, neither the anterior nor the posterior arches are fused. Fusion of the anterior arch is complete between 7 and 10 years of age. During the second year, the center of the posterior tubercle appears, and by the end of the fourth year, the posterior arch becomes complete.¹² Nonfusion of the anterior or the posterior arch, or both, exists as a normal variant in adults and should not be mistaken for fracture (Fig. 2-7).

Figure 2-7 Nonfused anterior (ant) and posterior (post) arches of C1, normal variant (axial computed tomogram with bone algorithm).

Pseudofractures of C2 and Dens

The second cervical vertebra, the axis (C2), is the largest and heaviest cervical segment. The C2 vertebra arises from five or six separate ossification centers, depending on whether the centrum has one or two centers. The vertebral body is ossified at birth, and the posterior arch is partially ossified. They fuse posteriorly by the second or third year of life and unite with the body of the vertebra by the seventh year.

The odontoid process (dens) serves as the conceptual body of C1, around which the atlas rotates and bends laterally. In contrast to the other cervical vertebrae, C2 does not have a discrete pedicle. The dens is situated between the lateral masses of the atlas and is maintained in its normal sagittal relationship to the anterior arch of C1 by several ligaments, the most important of which is the transverse atlantal ligament. Superiorly, the dentate (apical) ligament extends from the clivus to the tip of the dens. Alar ligaments secure the tip of the dens to the occipital condyles and to the lateral masses of the atlas. They are the second line of defense in maintaining the proper position of the dens. The tectorial membrane is a continuum of the posterior longitudinal ligament from the body of C2 to the upper surface of the occipital bone anterior to the foramen magnum.

The dens ossifies from two vertically oriented centers that fuse by the seventh fetal month. Cranially, a central cleft separates the tips of these ossification centers (Fig. 2-8), and it can mimic a fracture if ossification is incomplete. The ossiculum terminale, the ossification center for the tip of the dens, may be visible on plain films, conventional tomograms, or CT scans and unites with the body by age 11 or 12 years. Failure of the ossiculum terminale to develop or failure to unite with the dens may result in a bulbous cleft dens tip. A nonunited terminal dental ossification center, called the os terminale, may be mistaken for a fracture of the odontoid tip.

Figure 2-8 Cleft dens, normal variant (arrow) (axial computed tomogram with bone algorithm).

Hypoplasia of C2

The position and anatomy of the dens with respect to the anterior arch of C1 and the foramen magnum are worthy of attention. Congenital anomalies of the odontoid process, such as hypoplasia, can result in a loss of the buttressing action of the dens during extension and subsequent compression of neural elements. Examples of conditions that are associated with odontoid hypoplasia are the Morquio, Klippel-Feil, and Down syndromes; neurofibromatosis; dwarfism; spondyloepiphyseal dysplasia; osteogenesis imperfecta; and congenital scoliosis.^13,16 Patients with these conditions are predisposed to atlantoaxial subluxation and craniocervical instability, and hyperextension of the head for intubation should be avoided. In addition, congenital fusion of C2 and C3 (Fig. 2-9), whether occurring as an isolated anomaly or as part of Klippel-Feil syndrome, places added stress at the C1-C2 junction.

Figure 2-9 Congenital fusion of C2 and C3. Lateral cervical spine radiograph (A) and sagittal T1-weighted magnetic resonance (MR) study (B) demonstrate fusion of the C2 and C3 vertebral bodies (dotted arrow) and their lateral and posterior elements (solid arrow). Lateral radiograph (C) and T1-weighted MR cervical spine study (D) of a patient with Klippel-Feil syndrome demonstrate fusion of C2 to C3 and fusion of C4 to C6. Not surprisingly, a disc herniation is present at the point of greatest mobility at C3-C4.

c Acquired Pathology

Cervical Spondylosis

Cervical spine radiographs are obtained for the evaluation of cervical spondylosis (Fig. 2-10). The hypertrophic bone changes associated with this condition are well depicted on radiographic studies. Large anterior osteophytes that project forward may cause dysphagia and difficult intubation. The bone canal and neural foramina are assessed for stenosis; if stenosis is present, precautions can be taken when hyperextending the neck and positioning the patient to avoid exacerbation of baseline neurologic symptomatology. Calcification and ossification are well depicted on radiographic studies.

Figure 2-10 Cervical spondylosis. Lateral cervical spine radiograph demonstrates large anterior osteophytes (arrow) that indent the airway and oropharynx.

Ossification of the anterior longitudinal ligament and diffuse idiopathic skeletal hyperostosis have been reported as causes of difficult intubation.¹⁷ This can be readily appreciated on plain films. Another condition that may signal difficult intubation is calcification of the stylohyoid ligament (Fig. 2-11).¹⁸

Figure 2-11 Calcified stylohyoid ligament. A, Lateral cervical spine radiograph. B and C, Coronal computed tomograms with bone algorithm. Lateral cervical spine flexion (D) and extension (E) views are also shown. Black arrows indicate calcified stylohyoid ligaments, and white arrows indicate the laryngeal ventricle (at the level of the vocal cords). Notice the change in the level of the hyoid bone and vocal cords with flexion and extension of the neck. h, Hyoid bone; s, styloid process; t, calcified thyroid cartilage.

Inflammatory Arthropathies

Inflammatory arthropathies involving the atlantoaxial joint with subluxation are classically seen in patients with rheumatoid arthritis or ankylosing spondylitis. However, the underlying causes of atlantoaxial subluxation are quite different in these two entities. Ankylosing spondylitis is characterized by progressive fibrosis and ossification of ligaments and joint capsules. In rheumatoid arthritis, bone erosion, synovial overgrowth, and destruction of the ligaments occur. Patients with rheumatoid arthritis are not only susceptible to AP subluxation at the C1-C2 junction but also at risk for vertical subluxation of the dens. Whether this condition is referred to as “cranial settling,” superior migration of the odontoid process, or basilar invagination, the end result is the same.¹² The odontoid process protrudes above the foramen magnum, narrowing the available space for the spinal cord and potentially leading to cord compression with the slightest head extension (Fig. 2-12).¹³

Figure 2-12 Position of the dens in a normal patient (A), in a rheumatoid patient (B), and in a nonrheumatoid patient with basilar invagination and platybasia (C). A, Postmyelography computed tomogram with sagittal reformation demonstrates normal relationship of the dens with respect to the foramen magnum, brainstem, and anterior arch of C1. A normal atlantoaxial distance (AADI) is seen (arrow). B, T1-weighted sagittal magnetic resonance (MR) study of the cervical spine in a rheumatoid patient with erosion and pannus formation at the atlantoaxial joint resulting in increased AADI (arrow), posterior subluxation of the dens, and brainstem compression. C, Sagittal MR study of the brain in a nonrheumatoid patient shows normal AADI, but basilar invagination and platybasia have resulted in vertical subluxation of the dens and brainstem compression. The line drawn from the hard palate to the posterior lip of the foramen magnum is Chamberlain’s line (dotted line); basilar invagination is defined as extension of the odontoid tip 5 mm or more above this line. Also notice the fusion of the C2 and C3 vertebrae. The small, linear, dark line at the mid-C2 level is the subdental synchondrosis (white arrow).

In response to the effective foreshortening of the spine that occurs secondary to the superior migration of the odontoid process from inflammatory or degenerative disease, there is acquired rotational malalignment between the spine and larynx.¹⁹ The larynx and the trachea, because they are semirigid structures and as a result of the tethering effect of the arch of the aorta as it passes posteriorly over the left main bronchus, are predictably displaced caudally, deviated laterally to the left, rotated to the right, and anteriorly angulated. The effective neck length can be affected by superior migration of the dens, severe spondylosis with loss of disc space, or iatrogenic causes secondary to surgery. The soft tissues of the pharynx become more redundant owing to the relative shortening of the neck, which further obscures the view of the larynx. On laryngoscopy, the vocal cords are rotated clockwise. A rotated airway is suspected when the frontal view of the cervical spine demonstrates a deviated tracheal air column.

d Anthropologic Measurements

Historically, bony landmarks other than the spine that can be appreciated on a lateral cervical spine radiograph have been used in the anesthesia arena to preoperatively predict difficult laryngoscopy and endotracheal intubation on the basis of anatomic factors. Mandibular size, the ratios of the various measurements, and their relationship to the hyoid bone have been proposed as predictors of difficult laryngoscopy (Fig. 2-13).²⁰ These measurements are meant to reflect the oral capacity, the degree of mouth opening, and the level of larynx.^21,22 It is apparent that the causes of difficult laryngoscopy and endotracheal intubation are multifactorial. Combined with the clinical examination, anatomic measurements and findings assessed by x-ray studies can help alert the anesthesiologist to a potentially difficult airway. In this way, difficult laryngoscopy and endotracheal intubation can be anticipated and not unexpected.

Figure 2-13 Mandibular and hyoid measurements proposed as predictors of difficult laryngoscopy: 1, Anterior depth of mandible; 2, posterior depth of mandible; 3, mandibulohyoid distance; 4, atlanto-occipital distance; 5, thyromental distance. Laryngeal ventricle (solid arrow) demarcates the level of the larynx. The true vocal cords are just below the level of the laryngeal ventricle. e, Epiglottis; h, hyoid bone.

1 General Technique, Anatomy, and Basic Interpretation

The lateral cervical spine study with bone and soft tissue technique allows an incidental view of the aerodigestive tract and a gross assessment of the overall patency of the airway. Useful ossified cartilage or bony landmarks of the pharynx and larynx that can be appreciated on the lateral neck radiograph are the hard palate, hyoid bone, thyroid, and cricoid cartilages (Fig. 2-14). The hard palate is a bony landmark used to separate the nasopharynx from the oropharynx. The larynx can be thought of as being suspended from the hyoid bone. Muscles acting on the hyoid bone elevate the larynx and provide the primary protection from aspiration. The largest cartilage in the neck is the thyroid cartilage, which along with the cricoid cartilage acts as a protective shield for the inner larynx. The cricoid cartilage is the only complete cartilaginous ring in the respiratory system. It is located at the level where the larynx ends and the trachea begins.

Figure 2-14 Normal bony landmarks on a lateral cervical spine radiograph: 1, Hard palate; 2, hyoid bone; 3, calcified thyroid cartilage; 4, calcified cricoid cartilage; e, epiglottis.

Normal air-filled structures seen on lateral plain films are the nasopharynx, oropharynx, and hypopharynx. Air in the pharynx outlines the soft palate, uvula, base of the tongue, and nasopharyngeal airway (Fig. 2-15). Any sizable soft tissue pathology results in deviation or effacement of the airway. The tongue constitutes the bulk of the soft tissues at the level of the oropharynx. In children, and sometimes in adults, prominent lymphatic tissues such as adenoids and palatine tonsils may encroach on the nasopharyngeal and oral airways. Lingual tonsils are located at the base of the tongue above the valleculae, which are air-filled pouches between the tongue base and the free margin of the epiglottis.

Figure 2-15 Normal airway structures seen on a lateral cervical spine radiograph: 1, Hard palate; 2, soft palate and uvula; 3, air-filled vallecula; 4, epiglottis; 5, air-filled pyriform sinus; 6, air-filled stripe of laryngeal ventricle; C, noncalcified cricoid cartilage; h, hyoid bone; HP, hypopharynx; NP, nasopharynx; OP, oropharynx; t, thyroid cartilage.

The epiglottis is an elastic fibrocartilage shaped like a flattened teardrop or leaf that tapers inferiorly and attaches to the thyroid cartilage. The epiglottis tends to be more angular in infants than in adults. During the first several years of life, the larynx changes its position in the neck.^23,24 The free edge of the epiglottis in neonates is found at or near the C1 level, and the cricoid cartilage, representing the most caudal portion of the larynx, is at the C4-C5 level. By adolescence, the epiglottis is found at the C2-C3 level and the cricoid is at the C6 level. The adult epiglottis is usually seen at the C3 level, with the cricoid at C6-C7. However, the position of these structures in the normal population varies by at least one vertebral body level.

Sometimes visualized by a cervical spine radiographic study with soft tissue neck technique or on the CT scout view or the MR sagittal view of the neck is a transversely oriented, air-containing lucent stripe, located just below the base of the aryepiglottic folds, which indicates the position of the air-filled laryngeal ventricle (Fig. 2-16). This marks the position of the true vocal cords, which are just below this lucent stripe. Lateral to the aryepiglottic fold is the pyriform sinus of the pharynx. This anterior mucosal recess lies between the posterior third of the thyroid cartilage and the aryepiglottic fold. The extreme lower aspect of the pyriform sinus is situated between the mucosa-covered arytenoids and the mucosa-covered thyroid cartilage, at the level of the true vocal cords. The air column caudally represents the cervical trachea. On the AP view, the false and true vocal cords above and below the laryngeal ventricles may be identified, as well as the subglottic region and the trachea.

Figure 2-16 Normal airway structures seen on a computed tomographic lateral scout view (A) and on a T1-weighted, fat-suppressed postcontrast sagittal magnetic resonance cervical spine study (B): 1, Hard palate; 2, soft palate and uvula; 3, retropharyngeal or prevertebral soft tissue; 4, epiglottis; 5, arytenoid prominence; 6, trachea air column; h, hyoid bone; HP, hypopharynx; LV, laryngeal ventricle; NP, nasopharynx; OP, oropharynx.

The landmarks dorsal to the airway are shadows representing the normal soft tissue structures of the posterior wall of the nasopharynx, which is closely adherent to the anterior surface of the atlas and the axis and extends superiorly to the clivus and inferiorly to become continuous with the soft tissues of the posterior wall of the hypopharynx. The ligaments of the cervicocranium are critical to maintaining stability throughout this region; they are directly involved in the range of motion of the cervicocranium and anteriorly contribute to the prevertebral soft tissue shadow. Superimposed on these deep structures are the constrictor muscles and the mucosa of the posterior pharyngeal wall. The cervicocranial prevertebral soft tissue contour should normally be slightly posteriorly concave rostral to the anterior tubercle of C1, anteriorly convex in front of the anterior tubercle, and posteriorly concave caudal to the anterior tubercle, depending on the amount of adenoidal tissue and on the amount of air in the pharynx.

Adenoidal tissue appears as a homogeneous, smoothly lobulated mass of varying size and configuration. The anterior surface of the adenoid is demarcated by air anteriorly and inferiorly. The air inferior to the adenoids allows differentiation between adenoids and the presence of a nasopharyngeal hematoma, which is commonly associated with major midface fractures. In infants and young children, the soft tissues of the cervicocranium are lax and redundant. Depending on the phase of respiration and position, the thickness of the prevertebral soft tissues may appear to increase and may simulate a retropharyngeal hematoma. This finding may extend to the lower cervical spine. This anomaly becomes normal if imaging is repeated with the neck extended and during inspiration. By 8 years of age, the contour of the soft tissues should resemble that seen in adults. Of note, in pediatric patients, sedation may result in a decrease in AP diameter of the pharynx at the level of the palatine tonsils, in the soft palate, and at the level of the epiglottis.

In the lower neck (C3 to C7), the prevertebral soft tissue shadow differs from that in the cervicocranium because of the presence of the beginning of the esophagus and the prevertebral fascial space, which are recognized on the lateral radiograph as a fat stripe. By standard anatomic description, the esophagus begins at the level of C4; however, in vivo, the esophageal ostium may normally be found as high as C3 or as low as C6 and varies with the phase of swallowing and the flexion and extension of the cervical spine.²⁵ The prevertebral soft tissue thickness, the distance between the posterior pharyngeal air column and the anterior portion of the third or fourth vertebra, should not exceed one half to three quarters of the diameter of the vertebral body. In the opinion of Harris and Mirvis, only the measurement at C3 is valid, and it should not exceed 4 mm (Fig. 2-17).¹²

Figure 2-17 Prevertebral soft tissues seen on lateral cervical spine radiographic studies. A, Normal adult. B, Retropharyngeal abscess in a child. The arrow points to the anteriorly displace airway and increase in the prevertebral space between the vertebral column and the airway.

(Courtesy of Dr. Alan Schlesinger, Texas Children’s Hospital, Houston, TX.)

More caudally, at the cervicothoracic junction, assessment of the prevertebral soft tissues is based on contour rather than actual measurement. This contour should parallel the arch formed by the anterior cortices of the lower cervical and upper thoracic vertebral bodies.

In truth, plain film diagnosis of upper airway diseases has been supplanted by cross-sectional imaging, except in a few situations in which plain radiographic findings are pathognomonic of the disease. Two classic examples of plain film radiologic diagnosis are acute epiglottitis and croup.

2 Classic Plain Film Diagnosis

a Acute Epiglottitis

In acute epiglottitis (or supraglottitis, a more encompassing term), there is edema and swelling of the epiglottis with or without involvement of the aryepiglottic folds and arytenoids. The offending organism is usually Haemophilus influenzae. Airway compromise with a rapidly progressive course requiring emergency tracheostomy is a possibility if the entity goes unrecognized and untreated. In general, the infection is milder in adults than in children. This entity, usually a more indolent form, is making a comeback among patients with acquired immunodeficiency syndrome (AIDS).

The findings on plain film are swelling or enlargement of the epiglottis. On the conventional lateral radiograph of the neck, thickening of the free edge of the epiglottis can be appreciated and is referred to as the “thumb sign” (Fig. 2-18). The width of the adult epiglottis should be less than one third of the AP width of the C4 body. Cross-sectional imaging is superfluous. However, the degree of airway compromise can theoretically be quantified by 3-D reformation.

Figure 2-18 Epiglottitis. Lateral soft tissue examination of the neck during flexion in a child demonstrates an enlarged and swollen epiglottis (“thumb sign”). e, Epiglottis; h, hyoid; m, mandible; u, uvula.

(Courtesy of Dr. Alan Schlesinger, Texas Children’s Hospital, Houston.)

b Laryngotracheobronchitis or Croup

In laryngotracheobronchitis or croup, the subglottic larynx is involved. This condition affects younger children and has a less fulminant course than acute epiglottitis. The swelling of the soft tissues in the subglottic neck can be appreciated on an AP view of the neck (Fig. 2-19). There is usually a long segment narrowing of the glottis and subglottic airway with loss of the normal angle between the vocal cords and the subglottic airway. This has been referred to as the “steeple sign.” The hypopharynx is usually dilated because of the airway obstruction distally.

Figure 2-19 Croup. Anteroposterior soft tissue neck radiograph in an infant. Long segment narrowing of the subglottic airway is present (arrow) with loss of the normal angle between the vocal cords and the subglottic airway (“steeple sign”).

(Courtesy of Dr. Alan Schlesinger, Texas Children Hospital, Houston.)

c Foreign Body

Plain films are usually obtained in the initial assessment of suspected foreign body ingestion. In children, up to 50% of witnessed foreign body ingestions are asymptomatic.²⁶ Most foreign bodies are radiopaque, but wood and plastic usually are not visible on plain films. The radiopacity of ingested fishbone varies with the type of fish.²⁷ In the neck, ingested foreign bodies most often lodge at the level of the pyriform sinus (Fig. 2-20).

Figure 2-20 Foreign body, fishbone. A, Lateral radiograph of the cervical spine. B, Axial computed tomogram of the neck in a different patient. e, Tip of the epiglottis; FB, fishbone; h, hyoid.

1 General Technique

Before the advent of CT, chest radiography was routinely ordered to assess pulmonary and cardiovascular status, and it is still a cost-efficient examination that yields a great deal of general information. The most common views of the chest are the posteroanterior (PA), anteroposterior (AP), and lateral projections (Fig. 2-21). The PA chest view is obtained with the patient’s anterior chest closest to the film cassette and the x-ray beam directed from a posterior to an anterior direction. Alternatively, the AP chest view is done with the patient’s back closest to the film cassette and the x-ray beam directed in the anterior to posterior direction. The part of the chest closest to the film cassette is the least magnified; therefore, the cardiac silhouette is larger on the AP projection. The lateral projection is most often performed with the patient’s left chest closest to the film cassette for better delineation of the structures in the left hemithorax, which is more obscured by the heart on a PA projection.

Figure 2-21

Normal posteroanterior (PA) and lateral radiographic studies of the chest. A, Normal PA view of a woman with increased density at the lung bases related to overlying breast tissues. B, PA view of a man with lucent lungs. C, Normal lateral chest view. D, Lateral view of a patient with chronic obstructive pulmonary disease showing barrel-shaped chest with increased retrosternal air; notice that the lung base appears progressively more lucent overlying the dorsal spine. The carina is indicated by an asterisk. 10, 10th posterior rib; A, aorta; Lt, left bronchus; Rt, right bronchus; T, trachea.

Other common projections include the oblique, decubitus, and lordotic views. The oblique view is useful for assessing a lesion with respect to other structures in the chest. The decubitus view is helpful to assess whether an apparent elevated hemidiaphragm is being caused by a large subpulmonic pleural effusion. The lordotic view is helpful to look for a suspected small apical pneumothorax, which can also be accentuated on an expiratory-phase examination.

It is useful to train one’s eyes to analyze the chest radiograph systematically to cover the details of the chest wall, including the ribs, lungs (field and expansion), and mediastinal structures such as the heart and the outline of the tracheal-bronchial tree. On an adequate inspiratory film, the hemidiaphragms are below the anterior end of the sixth rib, or at least below the 10th posterior rib, and the lung expansion should be symmetrical. The right hemidiaphragm is usually half an interspace higher than the left, which is depressed by the heart (see Fig. 2-21A). Without doubt, the art of chest radiograph interpretation has diminished since the advent of CT, which demonstrates chest pathology with unparalleled clarity. However, chest radiography can still provide a composite survey of the chest at one quick glance. One can easily compare the lung volumes, identify the position of the mediastinum, determine the presence or absence of major airspace disease, and make a gross assessment of the cardiac status.

2 Interpretation of Pertinent Findings

a Level of Diaphragm

A high hemidiaphragm implies reduced lung volume, which can result from phrenic nerve paralysis, thoracic conditions causing chest pain that leads to splinting, or extrapulmonic processes such as an enlarged spleen or liver, pancreatitis, or subphrenic abscess. The presumed level of the hemidiaphragm is seen as an edge or transition between the aerated lungs and the opacity of the organs in the abdomen. If the thin leaves of the hemidiaphragm are outlined by air, a pneumoperitoneum should be considered (Fig. 2-22).

Figure 2-22 Pneumoperitoneum. Postoperative anteroposterior chest radiograph after thoracotomy. Arrows in right upper chest demarcate the thin pleural line defining a tiny pneumothorax. Arrow in right lower chest indicates the right hemidiaphragm outlined by a small pneumoperitoneum. This patient also has cardiomegaly and right midlung and left basilar atelectasis.

b Lung Aeration

A well-expanded lung should appear radiographically lucent but be traversed by “lung markings,” thin threads of interstitium consisting of septa and arterial, venous, and lymphatic vessels. In most normal individuals, the lungs appear more lucent at the top owing to the distribution of the pulmonary vasculature, the effect of gravity, and overlying soft tissues such as breast tissues. In patients with congestive heart failure or pulmonary venous hypertension, this pattern is reversed, with “cephalization” and engorgement of the pulmonary veins in the upper lung zones (Fig. 2-23; also see Fig. 2-21D). In general, any process such as fluid, pus, or cells that replaces the airspaces of the lungs causes the x-ray beam to be more attenuated, allowing less of the beam to be transmitted through the patient to the film. This causes the affected areas to appear less dark or more opaque (white) on the film. A whole host of diseases could be responsible, depending on the clinical picture, including pleural effusion, pulmonary edema, pneumonia, lung mass, lung collapse or atelectasis, lung infarct or contusion, and metastatic disease (Fig. 2-24). The key from an anesthesiologist’s point of view is not to make the correct pathologic diagnosis but to note the abnormality, which may affect ventilation, and adjust the anesthetic practice accordingly.

Figure 2-23 Congestive heart failure. Anteroposterior chest radiograph demonstrates engorgement of the perihilar vasculature. An endotracheal tube and a nasogastric tube are in place.

Figure 2-24 A and B, Left pleural effusion. Posteroanterior (PA) view of the chest (A) shows almost complete “white-out” of the left hemithorax and minimal residual aerated left upper lung zone. There is a mass effect with deviation of the trachea to the right. On the lateral view (B), the pleural effusion is less apparent. The tipoff is the lack of the expected lucency overlying the spine at the base (compare Fig. 2-21, C and D). C, Pulmonary edema. Anteroposterior (AP) view of the chest demonstrates bilateral hazy lung fields with air bronchogram. A tracheostomy tube is present. D through F, Left lower lung mass. Notice that although the inspiratory effort is the same on both the PA (D) and the AP (E) view (i.e., hemidiaphragm below ninth posterior rib), the cardiac silhouette and the left lower lobe mass appear larger on the AP view by virtue of the film geometry and magnification factor. The lateral view (F) helps to localize the disease process to the lateral segment of the left lower lobe. A mass is noted with postobstructive atelectasis (arrows). G and H, Aspergillosis. AP chest radiograph (G) shows nodular densities in both lungs. The differential diagnosis includes inflammatory and neoplastic processes. Notice that the tip of the endotracheal tube is in a good position, above the carina, and there is a central line on the right. Axial computed tomogram of the chest (H) better demonstrates the nodular pattern of lung involvement. I and J, Melanoma metastases to the lungs. The PA (I) and lateral (J) radiographs of the chest demonstrate nodular densities in both lungs in a patient with known melanoma. These examples show that radiographic findings are similar when the lung parenchyma is infiltrated with inflammatory or neoplastic cells.

In contrast to the increased opacity of the lung caused by the preceding conditions is a hemithorax, which appears too lucent and devoid of the expected lung markings. Two entities should be considered. Foremost is a pneumothorax (Fig. 2-25); if the pneumothorax is large, the collapsed lung will be medially applied against the mediastinum. If the mediastinum is shifted away from the midline, a tension pneumothorax may be present, and emergent management is required. More often than not, the cause is the presence in patients with chronic obstructive pulmonary disease of large emphysematous blebs, which are sometimes difficult to differentiate from a moderate to large pneumothorax.

Figure 2-25 Pneumothorax. Posteroanterior chest radiograph in a young man with spontaneous pneumothorax (arrows).

(Courtesy of Dr. John Pagani, IRPA, Houston.)

More rare causes of a unilateral lucent lung are pulmonary oligemia with decreased pulmonary flow from a thromboembolism of the right or left pulmonary artery, pulmonary neoplasm, and obstructive hyperinflation. Bilateral lucent lungs are harder to appreciate. These are usually seen in patients with pulmonary stenosis secondary to cyanotic heart disease and right-to-left shunts. A discussion of the pediatric chest and congenital heart and lung diseases is beyond the scope of this chapter.

c Mediastinum and Heart

The mediastinum lies centrally in the chest and contains the hila, tracheobronchial tree, heart and great vessels, lymph nodes, esophagus, and thymus. The mediastinum is extrapleural and is outlined by air in the adjacent lungs. Except for the air within the trachea and the main stem bronchi, the remainder of the mediastinal structures are soft tissues or of water density (including the fat) on conventional chest radiographs. Therefore, it is extremely difficult to localize a mediastinal lesion. Traditional pleural reflections or vertical lines have been described for a frontal chest radiograph that, if deviated, would suggest the presence of mediastinal pathology.

Felson proposed a radiologic approach to subdividing the mediastinum on a lateral radiograph into three compartments: anterior, middle, and posterior.²⁸ The anterior and middle mediastinum are divided by an imaginary line that extends along the back of the heart and front of the trachea. The middle and posterior mediastinal compartments are separated by a similar line that connects a point on each thoracic vertebra about 1 cm behind its anterior margin (Fig. 2-26).²⁸ Conditions that can be found in each of the compartments of the mediastinum are logically based on the anatomic structures found within the compartment. For example, tracheal, esophageal, and thyroid lesions would lie in the middle mediastinum. Neurogenic tumors and spinal problems would be in the posterior mediastinum. Cardiac and thymic lesions would occupy the anterior mediastinum. Certain diseases such as lymph node disorders, lymphoma, and aortic aneurysms may arise in any or all three compartments. Many modifications to the divisions of the mediastinum have been proposed.²⁹

Figure 2-26 Mediastinal compartments. Lateral chest radiograph with imaginary lines drawn on the film to demonstrate the three mediastinal compartments. The anterior (A) and middle (M) mediastinal compartments are divided by a line extending along the back of the heart and front of the trachea. A line connecting each thoracic vertebra about 1 cm behind its anterior margin separates the middle from the posterior (P) mediastinal compartment.

The great vessels and the heart should be centrally located on the AP view of the mediastinum. The aortic knob is usually on the left, and the cardiothoracic ratio on the AP view is roughly less than 50%. The hila are composed of the pulmonary arteries and their main branches, the upper lobe pulmonary veins, the major bronchi, and the lymph glands (Fig. 2-27).

Figure 2-27 Right hilar mass and nodes (arrows). Posteroanterior (A) and lateral (B) chest radiographs.

d Tracheobronchial Tree

The positions of the trachea, carina, and main stem bronchi are outlined by air. The carinal bifurcation angle is typically 60 to 75 degrees.²⁹ The right main stem bronchus has a steeper angle than the left (see Fig. 2-21); it usually branches off the trachea at an angle of 25 to 30 degrees, whereas the left main stem bronchus leaves the trachea at a 45- to 50-degree angle. The trachea is a tubular structure that extends from the cricoid cartilage to the carina, which is located approximately at the T5 level. C-shaped hyaline cartilage rings, which can calcify with age, outline the trachea anteriorly. The posterior trachea is membranous. The mean transverse diameter of the trachea is approximately 15 mm for women and 18 mm for men.²⁹ The trachea in the cervical region is midline, but it is deviated to the right in the thorax.

Endotracheal Tube Positioning

Adequate positioning of an endotracheal tube (ETT) in an intubated patient is usually documented by obtaining a chest radiograph. The tip should be intrathoracic and at a distance above the carina that ensures equal ventilation to both lungs. One should evaluate the position of the ETT with the patient’s head and neck in a neutral position; however, this may not be possible in an intensive care unit setting. The tip of the ETT may move up or down by 1 to 2 cm with flexion or extension of the head. Rotation of the head and neck usually results in ascent of the tip.²⁹ The optimal position of the tip of the ETT is 3 to 5 cm above the carina, to allow enough latitude in movement of the tube with turning of the patient’s head, and the inflated cuff should be below the vocal cords (Fig. 2-28).³⁰ Malpositioning of the cuff at the level of the vocal cords or pharynx increases the risk of aspiration. Overinflation of the cuff at the level of the vocal cords may lead to necrosis.³¹ The inflated cuff of the ETT should fill the tracheal air column without changing its contour. Overall, the ETT size should be about two thirds of the diameter of the tracheal lumen. At times, the tip of the ETT extends beyond the carina, resulting in intubation of the right main bronchus, which can be detected by asymmetrical breath sounds or on chest radiographs. If this condition goes unrecognized, atelectasis in the underaerated lung may result (Fig. 2-29).

Figure 2-28 Anteroposterior (AP) portable chest radiograph. Most chest examinations in the intensive care unit are obtained with a portable x-ray machine in the AP projection. Notice the acceptable position of the ETT above the carina. A right subclavian central venous line is present with the tip in the superior vena cava. Multiple cables attached to monitors are crossing the chest.

Figure 2-29 Endotracheal tube (ETT) in right main bronchus. Anteroposterior (AP) computed tomographic (CT) scout view obtained for CT soft tissue neck study reveals errant ETT in right main bronchus resulting in nonaeration of the left lung (white lung).

Nasogastric Tube Positioning

If a nasogastric or orogastric tube is in place, it should more or less course inferiorly and to the left, toward the fundus of the stomach in the left upper quadrant, except for the unusual case of situs inversus. If the gastric tube has inadvertently intubated the bronchus, the errant course of the tube will be evident on the plain film.

1 Imaging Anatomy Overview

Cross-sectional imaging of the nose and paranasal sinuses allows one to examine the air passage from the nares to the nasopharynx. A dedicated examination of the nose and sinuses yields detailed information about this region (Fig. 2-31). Incidental imaging of the sinuses and airway on a routine brain or spine study often allows general assessment of the airway that might be useful in the overall preoperative assessment of a patient (Fig. 2-32).

Figure 2-31 Axial (A through F) and coronal (G through J) computed tomographic studies showing the anatomy of the sinonasal cavity: 1, Hard palate; 2, base of nasal septum; 3, nostril; 4, ramus mandible; 5, styloid process; 6, anterior arch of C1; 7, nasal septum; 8, inferior turbinate; 9, nasopharynx; 10, right maxillary sinus; 11, left maxillary sinus with inflammatory mucosal disease; 12, lateral pterygoid plate; 13, medial pterygoid plate; 14, nasolacrimal duct; 15, rostrum sphenoid; 16, pterygoid process; 17, pterygopalatine fossa; 18, middle turbinate; 19, nasal cavity; 20, inferior orbital fissure; 21, foramen ovale; 22, foramen spinosum; 23, carotid canal; 24, zygomatic arch; 25, mandibular head; 26, nasal bone; 27, dorsum sella; 28, anterior clinoid; 29, calcified carotid artery; 30, nasofrontal suture; 31, perpendicular plate of ethmoid; 32, vomer; 33, hard palate; C, clivus; CG, crista galli; E, ethmoid sinus; EAC, external auditory canal; F, foramen magnum; G, globe; inf, inferior turbinate; mid, middle turbinate; OC, optic canal; ON, optic nerve; S, sphenoid sinus; SOF, superior orbital fissure; SOV, superior ophthalmic vein.

Figure 2-32 Airway as seen on routine studies. A, T2-weighted coronal magnetic resonance (MR) image of the brain demonstrates hyperintense, inflamed, thickened mucosa of the maxillary sinuses. B, T2-weighted axial MR image of the brain demonstrates sinus disease with a clear nasal cavity and nasopharynx. C, Sagittal reformation from computed tomographic neck examination demonstrates a clear airway from nose to trachea. D, T1-weighted sagittal MR cervical spine examination demonstrates signal void (black) of the air column of the airway. 1, Nasal cavity; 2, inferior turbinate; 3, nasopharynx; e, epiglottis; LNX, larynx; M, maxillary sinus with thickened mucosa.

The bony housing of the nose and the nasal cavities is well depicted by CT. By changing the viewing windows and level, one can delineate the soft tissue component to better advantage. The nasal cavity is divided into two cavities separated by the nasal septum. The roof of the nasal cavity is formed by the cribriform plate of the ethmoid. The hard palate serves as the floor. Protruding into the nasal cavities along the lateral walls are mucosa-covered, scroll-like projections of bone called the inferior, middle, superior, and supreme turbinates or conchae. The supreme turbinates are seen in only 60% of people.³³ The air space beneath and lateral to each turbinate, into which the paranasal sinuses drain, is referred to as the meatus.

In addition to clearly defining the anatomy, cross-sectional imaging can also be a window to viewing physiologic function, in particular the nasal cycle (the cyclic variation in the thickness of the mucosa of the nasal cavity), which repeats every 20 minutes to 6 hours.^33,34 This physiologic change is manifested as alternating side-to-side swelling of the turbinates.

2 Pertinent Imaging Pathology

a Congenital and Developmental Abnormalities

Congenital Choanal Stenosis and Atresia

The development of the nasal cavity is complete by the second month of fetal life. From the second to the sixth month of prenatal life, the nostrils are closed by epithelial plugs that later recanalize to establish a patent nasal cavity. Failure of this process could account for the congenital stenoses and atresias that cause nasal airway obstruction and are often seen in conjunction with craniofacial anomalies.³²

Congenital nasal airway obstruction most commonly occurs in the posterior nasal cavity secondary to choanal atresia (Fig. 2-33). The atresias may be bony, membranous, or both. At birth, severe respiratory difficulty and inability to insert an NGT more than 3 to 4 cm into the nose despite the presence of air in the trachea and lungs suggests the diagnosis of atresia. However, most atresias are unilateral, and may remain undetected until late in life.

Figure 2-33 Choanal atresia. Axial computed tomographic scan demonstrates posterior aperture stenosis on the right (arrow). The vomer (V) is enlarged.

Stenosis of the posterior nasal cavity (choanae) is probably more common than true atresia. About 75% of children with bilateral choanal stenosis or atresia have other congenital abnormalities such as Apert’s syndrome, Treacher Collins syndrome, or fetal alcohol syndrome. Because the pathology is usually manifested as bony overgrowth, CT is the imaging modality of choice. The major feature of atresia is an abnormal widening of the vomer (Fig. 2-34). Nasal airway obstruction may also result from rhinitis or turbinate hypertrophy.

Figure 2-34 Congenital nasal deformity. Axial computed tomographic scans demonstrate abnormal nasal bone architecture with soft tissue cleft and the impact on nasal airways.

Deviated Septum

The cartilage of the nasal capsule, which is the foundation of the upper part of the face, eventually becomes ossified or atrophied with age. All that remains of the cartilage of the nasal capsule in adults is the anterior part of the nasal septum and the alar cartilages that surround the nostrils. The midline septal cartilage is continuous with the cartilaginous skull base. At birth, the lateral masses of the ethmoid are ossified, but the septal cartilage and the cribriform plates are still cartilaginous. Another ossification center appears in the septal cartilage anterior to the cranial base and becomes the perpendicular plate of the ethmoid. In about the third to sixth year of life, the lateral masses of the ethmoid and the perpendicular plate become united across the roof of the nasal cavity by ossification of the cribriform plate, which unites with the vomer below somewhat later. Growth of the septal cartilage continues for a short time after craniofacial union is complete, and this probably accounts for what is commonly seen as deviated nasal septum.³²

Acquired bases of deviated septum also exist (e.g., trauma), and there is a varying degree of septal deviation, which can be associated with a prominent bony beak. In most cases, septal deviation is not problematic for NGT or nasal airway insertion, but having prior knowledge of the anatomy of the nasal cavity allows one to choose the path of least resistance.

Concha Bullosa

The term concha bullosa refers to an aerated turbinate, most often the middle turbinate, either unilateral or bilateral. In most cases it an incidental finding. However, it can be quite large and narrows the nasal air passage. Knowing which nasal cavity is narrowed by the presence of a concha bullosa helps guide the selection of which nasal cavity to cannulate (Fig. 2-35).

Figure 2-35 Concha bullosa. Axial computed tomographic scan demonstrates pneumatization (asterisk) of the left middle turbinate and deviated septum (S).

b Inflammatory Conditions

Rhinosinusitis

In general, no imaging is required for work-up of uncomplicated rhinosinusitis. Views of the sinus are included in a routine CT brain study. The air within the sinuses abuts the bony sinus wall and appears black on both CT and MRI. To assess the bony structures, CT is preferred. However, MRI is extremely useful to differentiate inflammatory disease from tumor. Inflammatory sinus disease is characterized by increased water content; therefore, an increased T2 signal (i.e., bright signal) is produced on T2-weighted imaging. Common inflammatory sinus disease is most often seen as T2-hyperintense lining of the walls of the sinus, representing thickened mucosa. In contrast, with increased cellularity, tumor masses typically exhibit an isointense signal on T2-weighted imaging. The most common local complications of inflammatory sinusitis are swollen turbinates, polyps, and retention cysts.

Polyposis

Nasal airway obstruction may result from rhinitis, polyposis, or turbinate hypertrophy. These entities affecting the airway are easily recognizable on cross-sectional imaging. Sensibly, the presence of polyposis may discourage an anesthesiologist from attempting nasal intubation (Figs. 2-36 and 2-37).

Figure 2-36 Antrochoanal polyp. Axial (A) and coronal (B) computed tomography scans demonstrate soft tissue obliterating the left nasal cavity and extending posteriorly into the nasopharynx (1) and laterally into the left maxillary sinus (2).

Figure 2-37 Nasal polyps. Axial computed tomography scans (A and B) demonstrate complete obliteration of the nasal passageways and pharynx by soft tissue polyps, resulting in chronic maxillary sinus inflammatory changes. 1, Nasal septum; 2, nasal cavity; NP, nasopharynx; M, maxillary sinus.

c Trauma

Facial fractures are often classified using the Le Fort system and its variants. This system is based on experiments predicting the course of fractures on the basis of lines of weakness in the facial skeleton. Nasal fractures are the most common facial fractures and may involve the nasal bones or the cartilaginous structures. If the nasal septum is fractured and a hematoma results, the vascular supply to the cartilage may be compromised, leading to cartilage necrosis. If the septal hematoma is not recognized and treated, it becomes an organized hematoma, which causes thickening of the septum and can result in impaired breathing (Fig. 2-38). Without doubt, CT is the modality of choice for evaluating trauma to the facial structures. Three-dimensional reconstruction and surface rendering can also be performed to better highlight fracture deformities. Even if all the details of a complex facial fracture are not known, an oral airway is preferable to a nasal airway, except in the case of mandibular fracture (Fig. 2-39), for which the nasal approach to intubation is preferred.

Figure 2-38 Nasal and septal fracture. Axial computed tomography scans (A and B) demonstrate comminuted fractures of the nasal bones bilaterally as well as a septal fracture. The nasal passages are further compromised by the incidental right concha bullosa (asterisk).

Figure 2-39 Mandibular fracture. Axial computed tomographic (CT) scans demonstrate typically paired fractures involving the right parasymphyseal body (A) and the left angle of the mandible (B). Notice the extensive air within the soft tissues. C, In another patient, three-dimensional surface rendering demonstrates a midline fracture of the mandible at the symphysis (arrows).

d Tumors and Other Conditions

Malignant Tumors

Malignant tumors of the nasal cavity and the paranasal sinuses are rare and have a poor prognosis because they are frequently diagnosed in an advanced stage. They are often accompanied by inflammatory disease. MRI is superior to CT in differentiating tumor from inflammatory disease and therefore is useful in delineating the tumor boundary from the often-associated inflammatory component. Inflammatory diseases involve a high water content; therefore, they have high T2-weighted intensity and appear bright on MRI. Nasal and paranasal tumors are usually cellular and have an intermediate-intensity signal on T2-weighted imaging (Fig. 2-40).^35,36 CT is useful for assessing bone involvement. The histology of the tumor can sometimes be suggested by the way in which the bone is affected: aggressive bone destruction is usually seen in squamous cell carcinomas (SCCs), metastatic lung and breast cancers, a few sarcomas, and rare fibrous histiocytomas (Fig. 2-41).

Figure 2-40 Esthesioneuroblastoma. A and B, T2-weighted axial magnetic resonance (MR) studies of the brain. Notice the large isointense soft tissue mass (m) in the nasal cavity, which is accompanied by obstructive inflammatory sinus disease of high T2 signal (s). The extension of the mass intracranially, indicated by the arrows, is better appreciated on the sagittal T1-weighted MR image of the brain (C) and on the coronal computed tomogram (CT) with contrast (D). Coronal CT better demonstrates bone destruction and also extension of the tumor to the right orbit.

Figure 2-41 A, Lymphoma of the nasal septum. Axial computed tomographic (CT) scan shows an infiltrating lesion of the anterior nasal septum (asterisk) that extends into the left maxillary soft tissues. B, Rhabdomyosarcoma of the right nasal cavity and nasal ala. Axial CT scan demonstrates a soft tissue mass (asterisk) effacing the right nostril.

Nonmalignant Destructive Tumors

Juvenile Nasopharyngeal Angiofibroma

Juvenile nasopharyngeal angiofibroma is a benign hypervascular tumor found almost exclusively in young adolescent men. It is a nonmalignant, locally destructive tumor of the sinonasal cavity. The most common presenting signs are unilateral nasal obstruction and spontaneous epistaxis. The tumor usually arises at the sphenopalatine foramen at the lateral nasopharyngeal wall and is locally destructive over time.³⁵ The imaging characteristics consist of a nasal cavity and nasopharyngeal mass, a widened pterygopalatine fossa, anterior displacement of the posterior wall of the maxillary sinus, and erosion of the medial pterygoid plate (Fig. 2-42). Treatment is surgical resection, often with preoperative embolization to decrease the blood supply.

Figure 2-42 Juvenile nasopharyngeal angiofibroma. A and B, Axial computed tomograms. C and D, Axial T1-weighted postcontrast magnetic resonance images. Anteroposterior (E) and lateral (F) views of digital subtraction angiogram. G, Lateral digital subtraction angiogram after embolization showing devascularization of the tumor. The soft tissue mass (m) extends from the pterygopalatine fossa (arrow in B) into the nasal cavity and nasopharynx.

Wegener’s Granulomatosis

Wegener’s granulomatosis, a necrotizing vasculitis, usually affects the upper and lower respiratory tracts and causes a renal glomerulonephritis. It is probably autoimmune in origin. It most often involves the nasal septum first and may arise as a chronic nonspecific inflammatory process. This process becomes diffuse, and septal ulcerations and perforations occur. Secondary bacterial infection often complicates the clinical and imaging picture (Fig. 2-43).³⁵

Figure 2-43 Septal pathologies narrowing the anterior nasal cavity are shown on axial computed tomography scans. A, A soft tissue mass is invading the right nasal cavity and orbit; it was diagnosed as Wegener’s granuloma. B, A septal granuloma is noted in association with focal bone destruction. C, A ring-enhancing lesion of the anterior septum is seen, consistent with a septal abscess.

Fibrous Dysplasia

Fibrous dysplasia, an idiopathic bone disorder, is not a tumor but can encroach on the airway and sinuses. Most patients are young at the time of diagnosis. There are monostotic and polyostotic forms. Craniofacial bones are more often involved in the polyostotic form (Fig. 2-44).³⁵

Figure 2-44 Fibrous dysplasia. A, Axial computed tomogram (CT) demonstrates a mass obliterating the left nasal cavity (asterisk) with the typical “ground glass” appearance of fibrous dysplasia involving the left skull base. B, Axial CT scan from a different patient demonstrates fibrous dysplasia with malignant degeneration to osteosarcoma invading the right nasal cavity and orbit (asterisk).

1 Imaging Anatomy Overview

CT and MRI are used extensively for evaluation of the oral cavity. The advantages of CT are the speed of data acquisition and the ability to detect calcifications pertinent in the evaluation of inflammatory diseases affecting the salivary glands. For evaluating the extent of tumor infiltration of the soft tissues, MRI is superior to CT; however, it is easily degraded by motion artifacts (Fig. 2-45).

Figure 2-45 Normal anatomy of the oral cavity is demonstrated on axial computed tomographic (CT) images (A, C, and E) with corresponding axial magnetic resonance (MR) scans (B, D, and F), on coronal CT (G) and coronal T1-weighted MR (H) scans, and on a sagittal T1-weighted MR image (I): 1, Median raphe of tongue (fat is low density on CT and bright on T1-weighted MR images); 2, tongue (transverse fibers are seen better on MR imaging); 3, uvula; 4, oropharynx; 5, pharyngeal constrictor muscle; 6, retromandibular vein; 7, internal carotid artery; 8, internal jugular vein; 9, cervical cord; 10, paired geniohyoid muscles; 11, mylohyoid muscle; 12, hyoglossus muscle; 13, lingual artery and vein medial to hyoglossus muscle; 14, Wharton’s duct, hypoglossal nerve, and lingual nerve lateral to hyoglossus muscle; 15, fat in sublingual space; 16, tongue base; 17, submandibular gland; 18, palatine tonsils narrowing oropharynx; 19, posterior belly of digastric muscle; 20, paired anterior belly of digastric muscle; 21, genioglossus muscle; 22, superior longitudinal muscle; 23, transverse muscle; e, epiglottis; h, body of hyoid bone; hp, hard palate; m, mandible; ms, maxillary sinus; p, parotid gland; scm, sternocleidomastoid muscle; sp, soft palate; ss, sphenoid sinus; v, vallecula.

The tongue consists of two symmetrical halves separated by a midline lingual septum. Each half of the tongue is composed of muscular fibers, which are divided into extrinsic and intrinsic muscles. There are four intrinsic tongue muscles: the superior longitudinal muscle, inferior longitudinal muscle, transverse muscles, and vertical muscles. The intrinsic muscles receive motor innervation from the hypoglossal nerve (cranial nerve [CN] XII) and participate in the enunciation of various consonants. The intrinsic muscles are difficult to distinguish on CT, but they are well visualized on MRI, because each muscle bundle is surrounded by high-intensity fibrofatty tissues.

The muscles that originate externally to the tongue but have distal muscle fibers that interdigitate within the substance of the tongue are considered to be extrinsic muscles of the tongue. The main extrinsic muscles are the genioglossus, hyoglossus, and styloglossus muscles. Sometimes the superior constrictors and the palatoglossus muscles are discussed with the extrinsic muscles of the tongue. The extrinsic muscles attach the tongue to the hyoid, mandible, and styloid process.

Motor innervation comes from the hypoglossal nerve, which courses between the mylohyoid and hyoglossus muscles. The sensory input from the anterior tongue is from the lingual nerve, which is a branch of the trigeminal nerve (CN V). Special sensory taste fibers from the anterior two thirds of the tongue course with the lingual nerve before forming the chorda tympani nerve, which subsequently joins the facial nerve (CN VII). The special sensory fibers from the posterior one third of the tongue (tongue base) are supplied by the glossopharyngeal nerve (CN IX). The arterial blood supply to the tongue is from branches of the lingual artery, which itself is a branch of the external carotid artery. Venous drainage is to the internal jugular vein.^25,38

The floor of the mouth is mainly composed of the mylohyoid muscles, the paired anterior bellies of the digastrics muscles, and the geniohyoid muscles. The space caudal to the mylohyoid muscle and above the hyoid bone is considered to be the suprahyoid neck. Through a gap between the free posterior border of the mylohyoid muscle and the hyoglossus muscle, the submandibular gland wraps around the dorsal aspect of the mylohyoid muscle.

Several named spaces and regions in the oral cavity are mentioned in brief because of their anatomic importance with respect to the structures contained within them. The sublingual region is below the mucosa of the floor of the mouth, superomedial to the mylohyoid muscle and lateral to the genioglossus-geniohyoid muscles. It is primarily fat filled and is continuous with the submandibular region at the posterior margin of the mylohyoid muscle. The contents of this space include the sublingual gland and ducts, the submandibular gland duct (Wharton’s duct) and sometimes a portion of the hilum of the submandibular gland, anterior fibers of the hyoglossus muscle, and the lingual artery and vein. The hyoglossus muscle is an important surgical landmark (see Fig. 2-45C). Lateral to this muscle, one can identify Wharton’s duct, the hypoglossal nerve, and the lingual nerve; the lingual artery and vein lie medially. Wharton’s duct runs anteriorly from the gland, traveling with the hypoglossal nerve and the lingual nerve (mandibular branch of the trigeminal nerve). Initially, it lies between the hyoglossus muscle and the mylohyoid muscle. More anteriorly, it lies between the genioglossus and mylohyoid muscles. The duct drains into the floor of the mouth, just lateral to the frenulum of the tongue.³⁹

The submandibular space or fossa is defined as the space inferior to the mylohyoid muscle, between the mandible and the hyoid bone. At the posterior margin of the mylohyoid muscle, the submandibular space is continuous with the sublingual space and the anterior aspect of the parapharyngeal space. This communication allows the spread of pathology. The submandibular space is primarily fat filled and contains the superficial portion of the submandibular gland and lymph nodes, lymphatic vessels, and blood vessels. The anterior bellies of the digastric muscle lie in the paramedian location in this space. Branches of the facial artery and vein course lateral to the anterior digastric muscle in the fat surrounding the submandibular gland. The artery lies deep to the gland, and the anterior facial vein is superficial.³⁸ One important anatomic point is that pathology intrinsic to the submandibular gland displaces the facial vein laterally. Other masses lateral to the gland, including nodes, can be identified with the vein interposed between the gland and the mass.⁴⁰

The lips are composed of orbicularis muscle, which comprises muscle fibers from multiple facial muscles that insert into the lips and additional fibers proper to the lips. The innervation to the lips is from branches of the facial nerve (CN VII). The vestibule of the mouth, or the gingivobuccal region, is the potential space separating the lips and cheeks from the gums and teeth. The parotid gland ducts and mucous gland ducts of the lips and cheek drain into this space, which is contiguous posteriorly with the oral cavity through the space between the last molar tooth and the ramus of the mandible.³⁸

2 Pertinent Imaging Pathology

a Macroglossia

The tongue makes up the bulk of soft tissues in the oral cavity. Enlargement of the tongue, which is defined clinically as protrusion of the tongue beyond the teeth or alveolar ridge in the resting position, compromises the oral airway and makes the insertion of airway devices challenging. Larsson and colleagues defined the appearance of macroglossia on CT imaging as (1) base of the tongue more than 50 mm in the transverse dimension, (2) genioglossus muscle more than 11 mm in the transverse dimension, (3) midline cleft on the tongue surface, and (4) submandibular glands normal in size but bulging out of the platysma muscle owing to tongue enlargement.⁴¹

There are congenital and noncongenital causes of macroglossia. The congenital syndromes in which macroglossia can be seen are trisomy 21, Beckwith-Wiedemann syndrome, hypothyroidism, and mucopolysaccharidoses. The more common noncongenital causes are tumor of the tongue, lymphangioma, hemangioma, acromegaly, and amyloid (Figs. 2-46 and 2-47). Rarely, infection can result in macroglossia, especially in an immune-compromised host (Fig. 2-48).

Figure 2-46 Macroglossia in a patient with a diagnosis of multiple myeloma and amyloid who developed an allergic reaction to amoxicillin clavulanate potassium (Augmentin). A, Axial computed tomographic (CT) image demonstrates the enlarged tongue occupying and extending beyond the oral cavity. There is no apparent oropharyngeal airway. A nasogastric tube is in place. B, Lateral CT scout view demonstrates the protrusion of the tongue beyond the confines of the oral cavity and diffuse soft tissue swelling on the neck.

Figure 2-47 Tongue hemangioma. Contrast-enhanced computed tomography (A) and magnetic resonance imaging (B) demonstrate an enhancing right tongue lesion that almost fills the oral cavity. C, The vascularity of the lesion is further demonstrated in the lateral view of the right external carotid angiogram. D, Angiogram after embolization shows devascularization of the tumor.

Figure 2-48 Mycobacterium avium-intracellulare infection in an immune-compromised patient. Axial computed tomogram with contrast demonstrates an irregular enhancement of lymph nodes and lymphoid tissue at the tongue base. The fungating tongue lesion (asterisk) compromises the oropharyngeal airway.

Posterior displacement of the tongue, or glossoptosis, may be observed with macroglossia, micrognathia or retrognathia, and neuromuscular disorders, including unilateral tongue paralysis secondary to hypoglossal nerve (CN XII) denervation. It can also occur in normal patients in some cases. The obvious complication is relative airway obstruction, which, if chronic, results in a myriad of systemic complications.

b Micrognathia and Retrognathia

Micrognathia is a term used to describe an abnormally small mandible. Retrognathia is defined as abnormal posterior placement of the mandible. These two findings often coexist. Abnormal growth or placement of the mandible can be caused by malformation, deformation, or connective tissue dysplasia.⁴² The most familiar syndromic form featuring an abnormal mandible is in the Pierre Robin sequence. Other clinical entities include the Treacher Collins, Stickler, and DiGeorge syndromes. Thin-section CT with 2-D or 3-D reformation provides information regarding the size and proportions of the maxilla, nose, mandible, and airway. Micrognathia and retrognathia not only contribute to airway obstruction but also are possible indicators of difficult direct laryngoscopy and endotracheal intubation that can lead to life-threatening complications (Figs. 2-49 and 2-50).⁴²

Figure 2-49 Midface regression syndrome in two patients with Jackson-Weiss syndrome and maxillary regression: computed tomographic scout view (A) and three-dimensional surface rendering (B). Notice the presence of a ventriculoperitoneal shunt; hydrocephalus may result from the craniosynostosis associated with this syndrome. The mandible is hypoplastic, and there is soft tissue obscuring the nasopharynx (arrow).

Figure 2-50 Treacher Collins syndrome. Axial computed tomographic (CT) scans at the level of the nasopharynx (A) and oropharynx (B) demonstrate almost complete obliteration of the airway by soft tissue, secondary to the facial microsomia. C, Lateral CT scout view demonstrates marked narrowing of the airway (arrow). D, Axial CT scan at the thoracic inlet demonstrates the tracheostomy necessitated by this condition.

c Exostosis

Hyperostosis of the hard palate or mandible is a benign disease that is usually of no clinical significance. Most often these are small exostoses. They may arise from the oral surface of the hard palate (torus palatinus), from the alveolar portion of the maxilla in the molar region along the lingual surface of the dental arch (torus maxillaris), or along the lingual surface of the mandible (torus mandibularis) (Fig. 2-51). Large lesions may restrict tongue motion and distort the airway, leading to speech disturbance.

Figure 2-51 Torus mandibularis. Axial computed tomogram at the level of the mandible demonstrates cortical widening of the lingual surface of the mandible.

1 Nasopharynx

a Imaging Anatomy Overview

The nasopharynx is an air-containing cavity that occupies the uppermost extent of the aerodigestive tract. The roof and posterior wall of the nasopharynx are formed by the sphenoid sinus, the clivus, and anterior aspect of the first two cervical vertebrae. The inferior aspect of the nasopharynx is formed by the hard palate, the soft palate, and the ridge of pharyngeal musculature that opposes the soft palate when it is elevated (Passavant’s ridge). The lateral nasopharyngeal walls are formed by the margins of the superior constrictor muscle. Anteriorly, the nasopharynx is in direct continuity with the nasal cavity through the posterior choanae. The nasopharynx is in direct communication with the middle ear cavity through the eustachian tubes (Fig. 2-52).⁴⁴

Figure 2-52 Normal anatomy of the nasopharynx. A, Computed tomographic (CT) scout view in prone position. B, T1-weighted sagittal brain magnetic resonance image. C, Normal nasopharynx on axial CT scan. D, Prominent adenoids effacing the nasopharyngeal airway. 1, Opening of the eustachian tube; 2, torus tubarius; 3, fossa of Rosenmüller; h, hyoid; hp, hard palate; NP, nasopharynx; OP, oropharynx; ss, sphenoid sinus; tb, turbinate, u, uvula.

b Pertinent Imaging Pathology

Adenoidal Hypertrophy

The adenoids are lymphatic tissues that are located in the upper posterior aspect of the nasopharynx. Prominent adenoids are typical in children; by the age of 2 to 3 years, the adenoids can fill the entire nasopharynx and extend posteriorly into the posterior choanae. Regression of the lymphoid tissue starts during adolescence and continues into later life. By the age of 30 to 40 years, adenoidal tissue is minimal, although normal adenoidal tissue may occasionally be seen in adults in the fourth and fifth decades of life. Adenoid tissues appear isodense to muscle on CT imaging (see Fig. 2-52D). On MRI, the adenoids are isointense to muscle on T1-weighted imaging and hyperintense on T2-weighted imaging. If prominent adenoidal tissue is seen in an adult, human immunodeficiency virus (HIV) infection should be suspected.⁴⁴ Differentiation between lymphomatous involvement and hypertrophy of the adenoids is not possible on imaging, because both entities are hyperintense on T2-weighted imaging. Enlargement of the adenoids can cause partial obstruction of the nasopharyngeal airway and make insertion of an NGT difficult. They may also contribute to the symptom complex of obstructive sleep apnea.

Tornwaldt’s Cyst

Tornwaldt’s cyst is a not uncommon incidental finding on MRI. It is usually midline and located between the longus capitis muscles in the posterior nasopharynx. It is a developmental anomaly in which the ascension of the notochord back into the skull base pulls a small tag of the developing nasopharyngeal mucosa with it, creating a midline pit or tract that closes over and results in a midline cyst, usually after pharyngitis. These lesions usually have a high signal intensity on T1- and T2-weighted imaging, probably because of the high protein content of the cyst fluid. Tornwaldt’s cyst is usually infected by anaerobic bacteria, which may empty into the nasopharynx and cause intermittent halitosis. The CT density of the cyst is similar to that of surrounding muscle and lymphoid tissue.

Infection and Abscess

Abscess in the parapharyngeal space may result from tonsillar infection or from iatrogenic or traumatic perforation of the pharynx. The infection may extend from the skull base to the submandibular region and can be difficult to differentiate from a neoplastic process. If large enough, it may compromise the airway. Infection spreading to retropharyngeal nodes (suppurative adenitis) can also obliterate the nasopharynx airway (Fig. 2-53).

Figure 2-53 Suppurative adenitis seen on axial computed tomography scans. A, A ring-enhancing mass (arrow) in the right parapharyngeal space is deviating the oropharynx. B, Bilateral bulky adenopathy is present with abscess formation obliterating the nasopharynx.

Tumors and Other Conditions

SCC of the nasopharynx is a relatively rare cancer that accounts for only 0.25% of all malignancies in North America. It has a high rate of incidence in Asia, however, where it is the most common tumor in men, accounting for 18% of cancers in China.⁴³ SCC accounts for 70% or more of the malignancies arising in the nasopharynx, and lymphomas account for about 20%. The remaining 10% are a variety of lesions, including adenocarcinoma, adenoid cystic carcinoma, rhabdomyosarcoma, melanoma, extramedullary plasmacytoma, fibrosarcoma, and carcinosarcoma. Risk factors for SCC in the nasopharynx include the presence of immunoglobulin A antibodies against Epstein-Barr virus, human leukocyte antigens HLA-A2 and HLA-B-Sin histocompatibility loci, nitrosamines, polycyclic hydrocarbons, poor living conditions, and chronic sinonasal infections.⁴⁴ The most common presentation is nodal disease. There is no correlation between primary tumor size and the presence of nodal disease. Imaging with CT and MRI is performed to map accurately the extent of the disease, not for histologic diagnosis (Fig. 2-54).

Figure 2-54 Squamous cell carcinoma (SCC) of the right nasopharynx. A, Axial computed tomogram (CT) with contrast demonstrates bulky soft tissue asymmetry in the nasopharynx with abnormal enhancement on the right. B, T1-weighted magnetic resonance image with gadolinium contrast confirms a right nasopharyngeal mass obstructing the eustachian canal and consequent opacification of the right mastoid air cells. C, Axial CT demonstrates SCC extending from the soft tissues of the left nasopharynx to the posterior fossa of the brain with bone destruction of the skull base. D, Axial CT after contrast enhancement. Notice the proximity of this invasive lesion to the vertebral artery (arrow) at the foramen magnum. If these findings are not appreciated at the time of surgery, an errant nasogastric tube can easily enter the cranium, damage the brainstem, and injure the vertebral artery. In each image, the mass is indicated by an asterisk. 1, Eustachian tube; 2, fossa of Rosenmüller; 3, opacified mastoid air cells.

2 Oropharynx

b Pertinent Imaging Pathology

Tonsillar Hypertrophy

During the third and fourth fetal months, lymphoid tissues invade the pharyngeal region of the adenoid tonsils, the palatine region (palatine tonsils), and the root of the tongue (lingual tonsils).³⁷ The adenoids are located in the roof of the nasopharynx. As mentioned previously, enlargement of the palatine and lingual tonsils may compromise the airway (Fig. 2-55).

Figure 2-55 Palatine and lingual tonsils. A, T2-weighted axial magnetic resonance (MR) image demonstrates bilateral hyperintense palatine tonsils (Pt) effacing the oropharynx. B, T1-weighted axial MR image shows enlarged lingual tonsils (Lt) effacing the vallecula (v); e, Epiglottis. C, Routine T1-weighted sagittal cervical spine study shows both palatine tonsils (Pt) and lingual tonsils (Lt) effacing the airway. The lingual tonsils push the epiglottis (e) dorsally.

Tonsillitis and Peritonsillar Abscess

Acute bacterial tonsillitis is most commonly caused by β-hemolytic streptococcus, staphylococcus, pneumococcus, or Haemophilus species. It is usually a self-limited disease; however, uncontrolled infection of the tonsils may result in a peritonsillar abscess or, rarely, a tonsillar abscess. On CT imaging, the findings of acute or chronic tonsillitis are nonspecific. Focal homogeneous swelling of the palatine tonsils can be present and is difficult to differentiate from tumor. The imaging features of abscess formation are a low-density center and an enhancing rim of soft tissue (Fig. 2-56). Peritonsillar abscess is the accumulation of pus around the tonsils. The infection may extend to the retropharyngeal, parapharyngeal, or submandibular spaces.

Figure 2-56 Tonsillar abscess. Axial computed tomogram with contrast demonstrates a left tonsillar fluid collection compressing the oropharynx.

Retropharyngeal Process

Infection of the retropharyngeal space usually results from an infection at a site whose primary drainage is to the retropharyngeal lymph nodes, such as the nose, sinuses, throat, tonsils, oral cavity, or middle ear. The lymph nodes enlarge and undergo suppuration and eventually rupture into the retropharyngeal space, creating an abscess. It can be caused by a penetrating injury or by cervical spine osteomyelitis or diskitis. Before the advent of antibiotics, retropharyngeal infection was potentially life-threatening. A retropharyngeal space infection can extend from the skull base to the carina. On imaging, a retropharyngeal abscess expands the prevertebral space, with enhancement along its margins.

Included in the differential diagnosis of a retropharyngeal abscess is tendinitis of the longus colli, which is characterized by inflammation of the tendinous insertion of the longus colli muscle with deposition of calcium hydroxyapatite crystals. An effusion may extend from the prevertebral space into the retropharyngeal space and mimic a retropharyngeal abscess. Post-traumatic hematoma may also increase the width of the prevertebral space. In addition, cervical spine pathology can extend and enlarge the prevertebral space and cause the airway to deviate anteriorly.

Tortuous Internal or Common Carotid Artery

If the course of either the common carotid artery or the internal carotid artery is directed medially, bulging of the submucosa of the oropharynx or hypopharynx may result. In this less protected location, the artery is more vulnerable to trauma. Imaging is useful to prevent unnecessary biopsy of this pseudosubmucosal mass (Fig. 2-57).

Figure 2-57 Anomalous course of carotids. A, Axial computed tomogram (CT) with contrast shows bilateral carotid aneurysms (an) effacing the oropharynx. Notice the presence of thrombus in the lumen of the aneurysm on the left. B, Axial CT with contrast demonstrates medially deviated carotids assuming a retropharyngeal location (arrows). IJ, Internal jugular vein.

Tumors and Other Conditions

SCC is the most common neoplasm of the oropharynx, and its predisposing factors include alcohol and tobacco use. Most recently, epidemiologic and molecular data have shown a strong association between human papillomavirus (HPV) infection—in particular, exposure to or infection with high-risk HPV-16—and the development of oropharyngeal cancer, especially tonsillar cancer. This subset of patients with oropharyngeal cancers present at a younger age and have distinct molecular and pathologic differences, with an as yet unexplained improved prognosis.⁴⁵ There is also a proven causal relationship between HPV-16 and the development of cervical cancer, and for this reason HPV infection is considered a sexually transmitted disease.

The site of origin determines the spread of the tumor; the most common locations are the anterior and posterior tonsillar pillars, tonsillar fossa, soft palate, and base of the tongue (Fig. 2-58). Staging of tumor in the oropharynx depends on the size of the tumor and whether it has invaded adjacent structures. Other neoplasms include lymphoma, minor salivary gland tumors, and mesenchymal tumors.

Figure 2-58 Squamous cell carcinoma of the tongue: axial contrast-enhanced computed tomography scans demonstrate a bulky enhancing lesion of the tongue (arrow) deforming the airway at the level of the oropharynx (A); nearly obliterating the airway and invading the floor of the mouth (B); and extending to the hypopharynx (C), where it fills the pre-epiglottic space.

3 Hypopharynx

The boundary of the hypopharynx is classically defined as the segment of the pharynx that extends from the level of the hyoid bone and the valleculae to the cricopharyngeus or the lower level of the cricoid cartilage. By definition, the cervical esophagus starts at the caudal end of the cricoid cartilage. The cricopharyngeus muscle acts as the superior esophageal sphincter. It arises from the lower aspect of the inferior constrictor muscle attached to the cricoid. The upper esophageal sphincter is normally closed until a specific volume and pressure in the hypopharynx trigger relaxation of the cricopharyngeus muscle to allow a bolus of food to pass into the cervical esophagus. The cricopharyngeus muscle then closes to prevent reflux.⁴³

a Imaging Anatomy Overview

The hypopharynx can be divided into four regions: the pyriform sinuses, the posterior wall of the hypopharynx, the postcricoid region, and the lateral surface of the aryepiglottic folds. The pyriform sinus is the anterolateral recess of the hypopharynx. The anterior pyriform sinus mucosa abuts on the posterior paraglottic space. The most caudal portion of the pyriform sinus lies at the level of the true vocal cords. The lateral aspect of the aryepiglottic folds forms the medial wall of the pyriform sinus (Fig. 2-59). This is considered a marginal zone because the aryepiglottic folds are part of both the hypopharynx and the supraglottic larynx. Tumors involving the medial surface of the aryepiglottic folds behave like laryngeal tumors. The biologic behavior of tumors arising from the lateral surface of the aryepiglottic folds is similar to that of the more aggressive pharyngeal tumors. The lateral wall of the pyriform sinus is formed by the thyroid membrane and cartilage.⁴⁴

Figure 2-59 Aryepiglottic fold and pyriform sinus. Axial computed tomogram at the level of hypopharynx. 1, Aryepiglottic fold; 2, air-containing pyriform sinus.

The posterior hypopharyngeal wall is continuous with the posterior wall of the oropharynx and begins at the level of the valleculae. It continues caudally as the posterior wall of the cricopharyngeus and the cervical esophagus. The retropharyngeal space lies behind the posterior pharyngeal wall. The anterior wall of the lower hypopharynx is referred to as the postcricoid hypopharynx: the larynx is anterior and the hypopharynx is posterior to this soft tissue boundary. It extends from the level of the arytenoid cartilages to the lower cricoid cartilage. On imaging, the transition from the hypopharynx to the cervical esophagus is denoted by a change in the shape of the aerodigestive tract, from crescentic or ovoid to round.

The arterial supply to the lower pharynx is mainly from the superior and inferior thyroid arteries. Venous drainage is through the superior and inferior thyroid veins and individual pharyngeal veins to the internal jugular vein.

b Pertinent Imaging Pathology

Pharyngitis

In immunocompetent patients, imaging is usually not required for the diagnosis or management of pharyngitis. In AIDS patients, imaging may be helpful to evaluate the extent of disease. Bacterial etiology is not the only concern; opportunistic infection with Candida or cytomegalovirus may involve the hypopharynx. These entities do not compromise the airway, but the mucosa is friable and is susceptible to injuries from instrumentation.

Pharyngocele

A pharyngocele is a broad-based outpouching of the pharyngeal mucosa of the upper pyriform sinus, which distends with phonation or during the Valsalva maneuver. These lesions are visible as air-filled structures on CT or as barium-filled areas on a barium swallow test.

Zenker’s Diverticulum

It is postulated that dyssynergy of the cricopharyngeus muscle plays a role in the formation of this pulsion diverticulum of the hypopharynx. The diverticulum typically extends posteriorly and laterally, usually to the left, and may appear as an incidental, air-filled structure in the hypopharynx on CT and MRI. If alerted to the presence of a diverticulum, one should take more caution during blind advancement of an NGT, which may take an errant course (Fig. 2-60).

Figure 2-60 Zenker’s diverticulum. A, Lateral cervical spine computed tomogram (CT) with soft tissue technique demonstrates an air-filled structure in the hypopharynx (white arrow) after anterior fusion. B, Axial CT at the level of the larynx shows the air-filled Zenker diverticulum to the right of midline (white arrow) and the tip of the right pyriform sinus (black arrow).

Trauma

Hematomas

Direct trauma or iatrogenic trauma caused by instrumentation, surgery, or a foreign body may result in retropharyngeal hematoma. Hemophiliacs may be more susceptible to hematomas with minor trauma. The imaging finding is retropharyngeal or prevertebral soft tissue swelling.

Postradiation Changes

The edema that occurs after radiation therapy may persist for many months or years and reflects a radiation-induced obliterative endarteritis. In cases of edema, the pharyngeal and supraglottic mucosa appears swollen, bulging, and hypodense on CT, and the submucosa fat is thickened and streaky. The platysma muscle and skin are also thickened. The end result is fibrosis and loss of elasticity of the soft tissues. This increased rigidity of the soft tissues should be taken into account during laryngoscopy for endotracheal intubation and in selecting the correct size of a laryngeal mask airway (LMA). Specifically, the LMA needs to be one or even two sizes smaller than predicted by the patient’s weight.

Tumors and Other Conditions

Squamous Cell Carcinoma

The hypopharynx is lined by stratified squamous epithelium, and most tumors of the hypopharynx are SCCs (Fig. 2-61). The risk factors for SCC of the hypopharynx include alcohol abuse, smoking, and previous radiation therapy. Patients with Plummer-Vinson syndrome have a higher incidence of postcricoid carcinoma. Extensive submucosal growth is common and can be appreciated only on imaging. The airway may be effaced and displaced. Most patients have metastases to the cervical nodes at presentation. Between 4% and 15% of patients with SCC of the hypopharynx have a synchronous or metachronous second primary tumor.^44,46

Figure 2-61 Squamous cell carcinoma of the hypopharynx. Axial computed tomogram with contrast demonstrates an enhancing mass (asterisk) involving the posterior wall of the hypopharynx with deformity of the airway. Notice the effacement of the right pyriform sinus. 1, Aryepiglottic fold; 2, pyriform sinus.

Lymphomas

Hodgkin’s lymphoma predominantly affects adolescents and young adults, whereas non-Hodgkin’s lymphoma is a disease of older patients. In contrast to patients with Hodgkin’s disease, patients with non-Hodgkin’s lymphoma present with disease in extranodal sites, such as Waldeyer’s ring. The imaging features of extranodal head and neck lymphoma can be difficult to differentiate from those of SCC. Lymphadenopathy in Hodgkin’s disease can be quite large without affecting the airways.

Other Malignancies

Less common primary cancers in the pharynx include minor salivary gland tumors (most often involving the soft palate), rhabdomyosarcomas, granular cell tumors, schwannomas and neurofibromas, hemangiomas, lipomas, amyloids, and metastases.^43,44

1 Imaging Anatomy Overview

Before the advent of CT and MRI, examination of the larynx consisted of plain radiographic films, multidirectional tomography, barium swallow, and laryngography. On a sagittal view, one can easily identify the hyoid bone, epiglottis, aryepiglottic folds, and vestibule, which is the space extending from the epiglottis to the level of the false vocal cords. At the level of the thyroid cartilage, a tiny slit of air is seen directed in the anterior-posterior direction. This is the laryngeal ventricle, which separates the false vocal cords from the true vocal cords (see Fig. 2-15).

Barium swallow, which is still used today, provides dynamic information about the swallowing mechanism and any dysfunction or incoordination of the muscles of swallowing and respiration. CT and MRI allow visualization of structures deep to the mucosa (Fig. 2-62); however, breathing and swallowing movements make imaging of the larynx difficult. The faster CT scanning technology available today allows the entire neck to be scanned in a single breath-hold. Helical technology allows reformation of the airway in multiple planes with one acquisition. MRI examination of the larynx continues to be problematic because of motion artifacts intrinsic and extrinsic to the larynx and longer acquisition time compared with CT. The advantage of MRI over CT is its ability to distinguish greater soft tissue contrast. The multiplanar capability of both CT and MRI is helpful in the evaluation of the mucosal folds and spaces in the neck.

Figure 2-62 Normal larynx. Axial computed tomographic (CT) scans at the level of the false cords (A) and the true vocal cords (B). The false cords (f) contain fat, which appears dark on CT and bright on T1-weighted magnetic resonance (MR) images. The true cords (t) are at the level of the arytenoid cartilage (a) and contain no fat. The subglottic airway is ovoid in shape, as shown in an axial CT scan (C). T-1 weighted sagittal (D) and coronal (E) MR images demonstrate the false cords (f) separated from the true cords (f) by the laryngeal ventricle (arrow).

In brief, the larynx can be considered as a conduit to the lungs. It also provides airway protection against aspiration and allows vocalization. It has an outer supporting skeleton comprising a series of cartilages, fibrous sheets, muscles, and ligaments that provides structure and protection for the inner mucosal tube, the endolarynx. Between the cartilages and the mucosal surface lie the paraglottic and pre-epiglottic spaces, which contain loose areolar tissues, lymphatics, and muscles. Superiorly, the larynx is suspended from the hyoid bone, which is attached to the styloid process at the base of the skull by the stylohyoid ligament. Calcification of the stylohyoid ligament (see Fig. 2-11) has been proposed as a cause of difficult intubation.¹⁸ Contraction of the muscles attached to the hyoid bone move it anterior and superior with consequent similar movements of the larynx. This sequence of movements also pulls the epiglottis to the horizontal plane, eventually inverting and closing the glottis and contributing to protection from aspiration.^47,48

The parts of the exoskeleton of the larynx that are visible on plain radiography include the arytenoid cartilage, the cricoid cartilage, and the thyroid cartilage, which is the largest cartilage of the larynx. The thyroid cartilage is made up of two shieldlike laminae that fuse anteriorly to form the laryngeal prominence (Adam’s apple). The angle of the fusion is usually more acute and more prominent in men. Paired superior and inferior cornua project from the posterior margin of the thyroid cartilage. The superior thyroid cornu is connected with the dorsal tip of the greater cornu of the hyoid bone by the thyrohyoid membrane. The inferior cornu articulates medially with the lateral wall of the cricoid cartilage to form the cricothyroid joint, where the thyroid cartilage rocks back and forth. Radiographically, this is an important landmark; it marks the entry of the recurrent laryngeal nerve to the larynx.³⁸ Muscles that attach to the external surface of the thyroid cartilage include the sternothyroid and thyrohyoid muscles and the inferior pharyngeal constrictors. The thyrohyoid membrane bridges the gap between the upper surface of the thyroid cartilage and the hyoid bone. Likewise, the cricothyroid membrane spans the distance between the lower margin of the thyroid cartilage and the cricoid cartilage.⁴⁷

The cricoid cartilage, which is shaped like a signet ring with the larger part facing posteriorly, is the base of the larynx. On the upper surface of the cricoid lamina are two paired articular facets, on which are situated the arytenoid cartilages. The arytenoid cartilages are important surgical and imaging landmarks.²⁵ Each cartilage is pyramidal in shape. The base is formed by two projections: the muscular process situated on the posterolateral margin and the vocal process located anteriorly. The muscular and vocal processes are at the level of the true vocal cords.

The corniculate cartilage sits at the apex of the pyramid and is located above the level of the laryngeal ventricle, at the level of the false vocal cords. The arytenoid cartilages are important in maintaining airway patency and participate in vocalization by altering the opening of the glottis and the tension of the vocal cords. This is achieved by movements between the arytenoid and cricoid cartilages: adduction, abduction, anterior-posterior sliding, and medial-lateral sliding.²⁵

For surgical planning purposes, the endolarynx can be divided into three compartments: the supraglottic larynx, the glottic larynx (glottis), and the subglottic larynx. The supraglottic airway can be defined as extending from the tip of the epiglottis to the laryngeal ventricles; it includes the false vocal cords, epiglottis, aryepiglottic folds, and arytenoids. The glottis is defined by the mucosal coverings of the true vocal cords and the anterior and posterior commissures. The subglottic larynx includes the undersurface of the true vocal cords and extends to the lower border of the cricoid cartilage.^38,47 The laryngeal ventricle demarcates two embryologically distinct laryngeal components: the supraglottic larynx and the subglottic larynx. The supraglottic larynx forms from primitive anlage and has richer lymphatics compared with the tracheobronchial buds. This embryologic and histologic difference accounts for the higher incidence of nodal metastasis at presentation of squamous cell cancer of the supraglottic larynx as compared to that of the glottic or subglottic primary.⁴⁷

Several structures in the endoskeleton of the larynx are worth describing. The epiglottis is a yellow elastic fibrocartilage; its tip defines the cephalad margin of the supraglottic larynx. It has a flattened teardrop or leaf shape that tapers to an inferior point called the petiole of the epiglottis, where it attaches to the thyroid cartilage through the thyroepiglottic ligament. The superior and lateral edges are free. Most of the epiglottis extends behind the thyroid cartilage; the tip may be above the hyoid bone and sometimes can be seen through the oral cavity. It is held in place and stabilized by the hyoepiglottic and thyroepiglottic ligaments. The hyoepiglottic ligament is a tough, fibrous, fanlike ligament that extends from the ventral midline of the epiglottis to the dorsal margin of the hyoid cartilage. Immediately above the ligament are the pharyngeal recesses, the valleculae, which are situated just caudal to the tongue base. The epiglottis helps to guard against aspiration; during swallowing, the aryepiglottic folds pull the sides of the epiglottis down, thereby narrowing the entrance to the larynx.^25,48

The quadrangular membrane stretches anteriorly from the upper arytenoid and corniculate cartilages to the lateral margin of the epiglottis and contributes to the support of the epiglottis.⁴⁷ The superior free margin of this membrane forms the support for the aryepiglottic fold, which stretches from the upper margin of the arytenoids to the lateral margin of the epiglottis. The corniculate and cuneiform cartilages within the aryepiglottic fold help support the edge of each fold. These small, mucosa-covered cartilages are visualized on laryngoscopy as two small protuberances at the posterolateral border of the rima glottidis.²⁵ The aryepiglottic folds form the lateral margin of the vestibule of the supraglottic airway. The upper part of the aryepiglottic fold is the aryepiglottic muscle, which functions like a purse string to close the opening of the larynx during swallowing. Lateral to the aryepiglottic folds are the pyriform sinuses. The apex, the most inferior aspect of the pyriform sinus, is at the level of the true vocal cords.

The inferior free margin of the quadrangular membrane forms the ventricular ligament, which extends anteriorly from the superior arytenoid cartilage to the inner lamina of the thyroid cartilage and supports the free edge of the false vocal cords. The false vocal cords are superior to the true vocal cords and are separated by a lateral pouching of the airway, the laryngeal ventricle.⁴⁷ A second set of ligaments, the vocal ligaments, lies parallel and inferior to the ventricular ligament. It also extends from the vocal process of the arytenoid cartilage to the inner lamina of the thyroid just above the anterior commissure. The vocal ligament provides medial support for the true vocal cords. The space between the left and right vocal cords is referred to as the rima glottis, through which air passes to allow breathing and vocalization. Extending from the vocal ligament is another fibrous membrane, the conus elasticus, which attaches inferiorly to the upper inner margin of the cricoid cartilage. The conus spans part of the gap between the thyroid and cricoid cartilages.^25,47

The muscles of the larynx are categorized as intrinsic and extrinsic muscles. The intrinsic muscles regulate the aperture of the rima glottis: (1) the thyroarytenoid makes up the bulk of the true vocal cord and has a lateral and a medial belly; (2) the lateral cricoarytenoids extend from the muscular process of the arytenoid cartilage to the upper lateral cricoid cartilage and function to adduct the cords; (3) the posterior cricoarytenoids extend from the muscular process of the arytenoid cartilage to the posterior surface of the cricoid cartilage and abduct the cords laterally; and (4) the intra-arytenoid muscle stretches from one arytenoid to the other and functions to adduct the vocal cords.^25,47 The extrinsic muscle is the cricothyroid muscle, which extends from the lower thyroid cartilage anteriorly to the upper cricoid cartilage. The contraction of this muscle pivots the thyroid cartilage forward around an axis through the cricothyroid joint, which stretches and tenses the vocal cords, thus affecting pitch in vocalization.^25,47

Because the vocal cords are not static structures, they are difficult to image. During normal respiration, the vocal cords are slightly abducted. During deep inspiration, the true vocal cords fully abduct against the lateral wall of the glottic airway. The airway opening becomes narrowed with medialization of the true cords during breath-holding with or without a Valsalva maneuver, expiration, and phonation. Extending below the true vocal cords to the cricoid cartilage is the infraglottic cavity. The trachea begins below the level of the cricoid cartilage.⁴⁷

The larynx is innervated primarily by branches of the vagus nerve.²⁵ The recurrent laryngeal nerve innervates all the intrinsic muscles of the larynx. If vocal cord paralysis is present and nerve damage is suspected, imaging should be tailored to follow the course of the recurrent laryngeal nerve in the neck and upper chest. The vagus nerve, after exiting the jugular foramen, passes vertically down the neck within the carotid sheath, between the internal jugular vein and the internal carotid artery (which becomes the common carotid artery) to the root of the neck. In front of the right subclavian artery, the recurrent laryngeal nerve branches from the vagus nerve, loops around the right subclavian artery, and ascends to the side of the trachea behind the common carotid artery, in the tracheoesophageal groove. On the left side, the recurrent laryngeal nerve arises at the level of the aortic arch. It loops around the arch at the point where ligamentum arteriosum is attached and ascends to the side of the trachea in the tracheoesophageal groove. The recurrent laryngeal nerve enters the larynx behind the cricothyroid joint and innervates all the muscles of the larynx except the cricothyroid muscle, which is an extrinsic muscle of the anterior larynx that is innervated by the external laryngeal branch of the superior laryngeal nerve, a branch of the vagus nerve in the neck. Sensory input from the laryngeal mucosa is by the internal laryngeal branch of the superior laryngeal nerve, which perforates the posterior lateral portion of the thyrohyoid membrane.²⁵

The blood supply to the larynx is from two branches of the external carotid artery: the superior and inferior laryngeal arteries. The superior laryngeal artery, a branch of the superior thyroid artery, travels with the internal branch of the superior laryngeal nerve. The inferior laryngeal artery, a branch of the inferior thyroid artery, which is a branch of the thyrocervical trunk, accompanies the recurrent laryngeal nerve into the larynx.²⁵

2 Pertinent Imaging Pathology

a Trauma

Fracture of the larynx, which usually occurs as a result of a vehicular accident, can involve the thyroid cartilage, the cricoid cartilage, or both. Laryngotracheal separation is usually fatal. Dislocation of the arytenoids relative to the cricoid cartilage may be encountered. Malalignment of the thyroid and cricoid cartilages results in dislocation of the cricothyroid joint. On imaging, the presence of air in the paraglottic soft tissues is an indication of laryngeal trauma (Fig. 2-63).

Figure 2-63 Laryngeal fracture. Precontrast (A) and postcontrast (B) axial computed tomography scans show extensive deep fascial emphysema as well as multiple fractures of the thyroid and cricoid cartilages.

Foreign bodies may be present due to trauma but are more commonly the result of ingestion or aspiration. The pyriform sinus is a common location for a foreign body. If the foreign body enters the larynx, it usually passes through to the trachea or a bronchus. Burn injury to the larynx can be caused by inhalation or ingestion of hot material. The supraglottic larynx is most likely to be involved, and generalized edema can occur.

b Vocal Cord Paralysis

Vocal cord paralysis may be characterized as either a superior laryngeal nerve deficit, a recurrent laryngeal nerve deficit, or a total vagus nerve deficit. The entire course of the vagus nerve and the recurrent laryngeal nerve should be imaged when assessing vocal cord paralysis (Fig. 2-64).

Figure 2-64 Causes of vocal cord paralysis in three different patients. In patient 1, there is right vocal cord paralysis secondary to tumor invasion. An axial computed tomographic (CT) scan (A) demonstrates squamous cell carcinoma invading the right vocal cord, which is medially deviated. In patient 2, there is right vocal cord paralysis secondary to tumor in the tracheoesophageal groove involving the recurrent laryngeal nerve. An axial contrast-enhanced CT scan (B) demonstrates a paralyzed right true vocal cord. In this case, denervation results from neural compromise in the tracheoesophageal groove due to papillary carcinoma of the right thyroid tumor (C). The paralyzed right cord is visualized endoscopically in D. In patient 3, a contrast-enhanced coronal T1-weighted magnetic resonance image (E) and an axial CT scan (F) demonstrate an enhancing vagus nerve schwannoma (asterisk) in a patient with known neurofibromatosis. Notice the normal vagus nerve (arrow), which is located within the contralateral carotid sheath, together with the carotid artery and jugular vein. This patient presented with right vocal cord paralysis.

The superior laryngeal nerve, through the external laryngeal branch, innervates only one muscle of the larynx—an extrinsic muscle, the cricothyroid muscle. This muscle extends between the thyroid and cricoid cartilages. As the muscle contracts, the anterior cricoid ring is pulled up toward the lower margin of the thyroid cartilage. This action rotates the upper cricoid lamina (and thus the arytenoids) posteriorly and puts tension on the true vocal cords. If one side is paralyzed, contraction of one muscle rotates the posterior cricoid to the contralateral paralyzed side.

More commonly, vocal cord paralysis is caused by recurrent laryngeal nerve pathology. All of the laryngeal muscles, except for the cricothyroid muscle, are innervated by this nerve. Most findings are secondary to atrophy of the thyroarytenoid muscle, the muscle that contributes to the bulk of the true vocal cords. The vocal cords become thinner and more pointed. Compensatory enlargement of the ventricle and the pyriform sinus is seen.⁴⁷ In the more acute phase, the paralyzed cord appears flaccid, prolapses medially because of the lack of muscular tone in the thyroarytenoid muscle, and demonstrates a lack of movement during breathing maneuvers and phonation.

d Tumors and other Conditions

Benign Tumors

Benign masses encountered in the larynx include vocal cord nodules, juvenile papillomatosis, and other nonepithelial tumors such as hemangiomas, lipomas, leiomyomas, rhabdomyomas, chondromas, neural tumors, paragangliomas, schwannomas, and granular cell tumors.⁴²

Cysts and Laryngoceles

Mucus-retention cysts can occur along any mucosal surface, but they are most common in the supraglottic larynx. Laryngoceles may be internal, external, or both. The common finding in a supraglottic mass is its connection with the laryngeal ventricle (Fig. 2-65).^42,47

Figure 2-65 Laryngocele. Axial contrast-enhanced computed tomographic scan demonstrates a fluid-filled internal laryngocele on the left (arrow).

Malignant Neoplasms

Most laryngeal tumors are malignant, and SCC is the most common type. These cancers arise on the mucosal surface and can be readily visualized by direct endoscopy. Imaging with CT and MRI is used to define the extent of the disease. Cross-sectional imaging is useful to assess the degree and direction of airway compromise (Fig. 2-66). Other cell types found are adenocarcinoma, verrucous carcinoma, and anaplastic carcinoma. More rare tumors are sarcoma, melanoma, lymphoma, leukemia, plasmacytoma, fibrous histiocytoma, and metastatic disease.⁴⁷

Figure 2-66 Laryngeal carcinoma. A through C, Axial contrast-enhanced computed tomographic scans. Squamous cell carcinoma extends from the right aryepiglottic fold (a) through the level of the arytenoids, to the cricoid (c), with cartilage destruction and invasion of the right vocal cord and strap muscles. The left thyroid cartilage (t) is intact, and the right is destroyed by tumor.

1 Imaging Anatomy Overview

Radiologic evaluation of the trachea includes plain films of the neck and chest, CT, and MRI. A lateral view of the neck provides a good screening examination for the cervical trachea. Chest radiography allows an initial assessment of the thoracic trachea and mediastinal structures. CT, and especially helical CT, is superior for evaluation of the tracheal anatomy and pathology because it allows direct visualization of the cross-sectional trachea. With multiplanar reconstruction, the degree and length of stenosis can be fully assessed. Virtual bronchoscopy, which is a 3-D reconstruction of helical CT data, allows simulated navigation through the tracheobronchial tree. MRI so far has limited use owing to its longer scanning time, intrinsic artifacts from breathing motion, and limited resolution.

2 Pertinent Imaging Pathology

Early detection of tracheal pathology is unusual because significant compromise of the airway can be present before symptoms manifest. More than 75% occlusion of the luminal diameter at rest, and more than 50% occlusion during exertion, must be present before symptoms of airway obstruction are manifested.⁵⁰ If symptoms are present, a superior mediastinal mass is often found on PA chest radiography. Also, the tracheal air column may be deviated or narrowed. Rarely, tracheal enlargement occurs as a result of tracheomalacia in patients with cystic fibrosis or Ehlers-Danlos complex. Pathology affecting the trachea can largely be classified as extrinsic or intrinsic diseases.

a Extrinsic Tracheal Pathology

Thyroid Goiter

One of the more common extrinsic pathologies affecting the cervical and substernal trachea is a goiter of the thyroid gland. The trachea is usually displaced laterally, and luminal compression is evident. Vocal cord paralysis, hoarseness, dyspnea, and dysphagia may be the presenting symptoms. These symptoms are all predictable and are predicated on the location of the goiter with respect to the trachea, the esophagus, and the recurrent laryngeal nerve. The lateral and posterior extension of abnormal soft tissue with respect to the larynx displaces the airway anteriorly and laterally and may be a cause of difficult intubation (Fig. 2-67).

Figure 2-67 Goiter. Anteroposterior computed tomogram (A) and lateral scout film (B) demonstrate a clinically obvious thyroid mass. Notice the tracheal deviation in image A (arrow) and the anterior displacement of the airway in image B. C and D, Axial images (referenced on the lateral scout view) further demonstrate the mass effect on the airway from the level of the hyoid to the thoracic inlet.

Thyroid Carcinoma and Nodes

As in the case of thyroid goiter, any mass involving or enlarging the thyroid gland can result in airway displacement and compression (Fig. 2-68). Enlarged lymph nodes secondary to lymphoma or metastatic disease can also cause extrinsic compression of the trachea.

Figure 2-68 Tracheal displacement and effacement on axial computed tomography (CT) scans of a patient with medullary carcinoma of the thyroid. A, CT scan demonstrates the right thyroid mass displacing the airway anteriorly and to the contralateral side. B, The tumor has destroyed the cricoid cartilage on the right and abuts the subglottic airway.

Vascular Rings and Slings

Vascular rings encircle both the trachea and the esophagus with airway compression. The most common example is the double aortic arch. Vascular slings are noncircumferential vascular anomalies that may cause airway compromise. The trachea may be compressed posteriorly from a pulmonary artery sling, in which the left pulmonary artery arises from the right pulmonary artery. It can also be compressed from the front by the innominate artery or an aberrant left subclavian artery.

c Non-Neoplastic Tracheal Narrowing

The intrinsic pathology of diffuse tracheal narrowing results from trauma due to aspiration of heat or of caustic or acid chemicals, radiation therapy, or intubation injury; additional unusual causes include sarcoidosis, Wegener’s granulomatosis, fungal infection, croup, and congenital conditions (Fig. 2-69).

Figure 2-69 Tracheal stenosis. A, Coronal reformatted computed tomographic (CT) image in a child demonstrates marked subglottic narrowing of the trachea. B, Axial CT in the same patient further defines the severity of narrowing.

Tracheomalacia

Tracheomalacia is characterized by abnormal flaccidity of the trachea resulting in collapse of the thoracic tracheal segment during expiration. There is softening of the supporting cartilage and widening of the posterior membranous wall, which may balloon anteriorly into the airway. Tracheomalacia can be divided into primary intrinsic and secondary extrinsic forms. Patients may have minimal or severe symptoms depending on the degree of airway obstruction.

Congenital Stenosis (Subglottic or Tracheal)

Congenital stenosis is uncommon and is usually associated with other congenital anomalies. The affected segment has rigid walls with a narrowed lumen, and the cartilages can be complete rings. The stenotic segment can be focal, or the entire trachea may be affected. Symptoms usually arise within the first few weeks or months of age. Most patients are treated conservatively.

Tracheoesophageal Fistula

TEF is a common congenital anomaly, with an incidence of 1 in 3000 to 4000 births. TEF is often associated with esophageal atresia.⁵⁰ There are several forms of TEF. The most common is a proximal esophageal atresia with a distal TEF. This anomaly may be associated with severe neonatal respiratory distress and may necessitate emergent tracheostomy. It is not uncommon for more than one fistula to be present, and there may be other associated anomalies affecting the cardiovascular, gastrointestinal, renal, or central nervous system (Fig. 2-70).

Figure 2-70 Tracheoesophageal fistula (TEF). Oblique radiograph from a swallow study with contrast outlines a classic H-type TEF.

(Courtesy of Dr. Netta Marlyn Blitman, Montefiore Medical Center, Bronx, NY.)

d Tumors and Other Conditions

Most benign tracheal neoplasms are found in pediatric patients. Squamous cell papilloma, fibroma, and hemangioma are the most common types. In adults, the most common benign tumors are chondroma, papilloma, fibroma, hemangioma, and granular cell myoblastoma.

Primary malignant neoplasms of the trachea are uncommon; laryngeal and bronchial primary tumors are much more common. In adults, however, primary neoplasms of the trachea are more common than benign tumors. The most common malignant tumor is SCC.⁵⁰

The trachea may be secondarily involved by metastatic disease, either from a remote primary tumor or by direct invasion, such as from a thyroid primary (Fig. 2-71).

Figure 2-71 Tracheal invasion from follicular carcinoma of the thyroid. Axial computed tomography scan demonstrates a mass on the right that is deviating and invading the trachea.