Computed Tomography

CT makes use of ionizing radiation to generate cross-sectional images based on differences in x-ray attenuation of various tissues. Modern scanners are typically helical, meaning that x-ray source rotation and patient translation occur simultaneously, resulting in the acquisition of a volume of data that is then partitioned and reconstructed into individual slices.¹ Helical scanning allows for rapid data acquisition to diminish artifacts related to motion (breathing, swallowing, gross patient motion). The rapid data acquisition also allows for more and thinner slices to be obtained, which facilitates diagnosis by decreasing partial volume averaging effects. It also allows for improved quality of multiplanar reconstructions. The most recent advance in CT imaging has been the introduction of the multidetector or multislice scanners.^2,3 Multidetector scanners have a variable number of parallel arcs of detectors that are capable of simultaneously acquiring volumes of data. The increased speed that results from multislice sampling can be traded for improved longitudinal resolution, increased volume of coverage, and improved signal-to-noise ratio.

CT of the head and neck should be performed with thin sections, generally ≤3 mm, in the axial plane (Fig. 17-1A). Direct coronal imaging may be performed in some situations (such as paranasal sinus imaging), but multidetector methods allow for high-quality coronal and sagittal reformations (Fig. 17-1B to Fig. 17-1E); reformatted images improve depiction of anatomical relationships and can improve diagnostic accuracy. They also spare the patient from additional radiation. Additional angled views can also be useful in specific situations (e.g., to throw artifacts related to dental amalgam off of vital structures) (Fig. 17-1F to Fig. 17-1H). Unless one is primarily interested in bony structures, CT of the head and neck is usually performed following injection of iodinated contrast material. The opacification of vessels helps to separate them from other structures such as lymph nodes and also helps to delineate pathologic conditions. Iodinated contrast material carries a small risk of minor or significant allergic reaction and a risk of nephrotoxicity in patients who already have some degree of renal dysfunction or are at risk of this (e.g., diabetics). These factors should be considered when a contrast-enhanced CT scan is requested.

CT is useful in the very ill or uncooperative patient in whom MRI is compromised by patient motion. CT is also useful in patients for whom MRI is contraindicated by the presence of ferromagnetic aneurysm clips, cardiac pacemakers, or other such devices. CT easily demonstrates differences in attenuation among air, bone, fat, and soft tissue, but is far less sensitive to subtle differences in tissue composition than is MRI. In the head and neck, CT is excellent for imaging the larynx and most cervical nodal groups. CT is also useful for assessing bone destruction and may be useful for planning reconstructive surgeries. MRI generally provides more information about the soft-tissue extent of primary tumors and better information about skull-base involvement, perineural spread of disease, and intracranial extension.

Magnetic Resonance Imaging

MRI exploits differences in tissue relaxation characteristics and spin density to produce an image that is exquisitely sensitive to soft-tissue contrast.^4,5 Depending on the parameters that one selects, variable tissue characteristics and contrast will be produced. Multiple types of sequences in multiple planes are generally necessary to fully characterize lesions of the head and neck. Slice thickness should be no more than 5 mm, and a gadolinium-based contrast agent is generally used to enhance detection of pathologic conditions and improve tissue characterization and differential diagnosis. In some circumstances, thinner sections covering a smaller anatomic area may be necessary for more precise depiction and diagnosis.

In the head and neck, we typically obtain the following imaging sequences:

Sagittal, axial, and coronal T₁-weighted images

Axial fast spin-echo (FSE) T₂-weighted images with fat saturation

Axial and coronal postgadolinium T₁-weighted images with fat saturation

On a T₁-weighted image, fat is bright and fluid (such as cerebrospinal fluid) is relatively dark. Muscle and most pathologic conditions are of intermediate signal intensity. The large amount of fat in the head and neck provides intrinsic tissue contrast, which makes the T₁-weighted image very sensitive to infiltrative processes that obliterate tissue planes or replace marrow fat (Fig. 17-2A). Some hemorrhagic or proteinaceous lesions may result in intrinsic T₁-shortening such that they appear bright on a T₁-weighted image. On a T₂-weighted image, fluid is very bright and most pathologic conditions are relatively bright, whereas muscle is quite dark. The FSE technique is useful in limiting artifacts related to motion and magnetic susceptibility as compared with a conventional spin-echo T₂-weighted image. Because fat remains bright on a FSE image, however, fat saturation should ideally be applied. In the nasal cavity and paranasal sinuses, T₂-weighted images are particularly useful in distinguishing neoplastic masses from polyps, thickened mucosa, and retained secretions (Fig. 17-2B). Gadolinium is useful for demonstrating pathologic conditions and tailoring a differential diagnosis based on enhancement characteristics. Postgadolinium imaging is also useful in assessing perineural spread of tumor, cavernous sinus invasion, and meningeal or brain infiltration (Fig. 17-2C and Fig. 17-2D). Fat saturation should ideally be applied on a postgadolinium image; otherwise, the contrast between an enhancing lesion and surrounding fat may actually be reduced as compared with the pregadolinium image. As low-field scanners often do not have fat saturation available, high-field (≥1.5 T) imaging is generally preferred for patients with head and neck cancer. If a patient is severely claustrophobic, then sedation may be necessary to accomplish the scan.

FIGURE 17-2 • A, An axial T₁-weighted image is shown. Note that fat (as seen in the subcutaneous region, subcutaneous fat [FAT], and also in the marrow of the clivus [C]) is extremely bright, whereas fluid (as seen in cerebrospinal fluid (CSF) in the prepontine cistern and Meckel cave (M) is dark. Soft tissue such as muscle and brain parenchyma are intermediate in signal intensity, whereas air (as in the sphenoid sinus [SS]) is black. The white arrowhead indicates the flow void of the basilar artery. White arrows indicate nasopharyngeal carcinoma infiltrating the fat of the right pterygopalatine fossa, which appears expanded and of lower signal intensity than the normal, mostly fatty pterygopalatine fossa on the left. B, A coronal fast spin-echo (FSE) T₂-weighted image with fat saturation is shown. Note that the signal from subcutaneous fat (FAT) is completely suppressed. Fluid appears bright, as seen with CSF in a cerebral sulcus (arrowheads) and the vitreous humor within the ocular globe (G). Mucoid material (M) within the maxillary, frontal, and ethmoid sinuses is extremely bright. In contrast, a highly cellular inverting papilloma (white arrows) is of intermediate signal intensity and shows clearly in contrast to thickened mucosa and sinonasal secretions. C, A postgadolinium axial T₁-weighted image with fat saturation is shown. Subcutaneous fat appears dark because its signal has been suppressed. Gadolinium administration can be confirmed by looking at the sinonasal mucosa, which enhances brightly postgadolinium. Orbital fat appears bright because of local failure of fat saturation resulting from inhomogeneity of the local magnetic field caused by the proximity to the air-filled maxillary sinuses. Abnormal enhancement is seen along foramen rotundum (white arrows) and in the Meckel caves (white arrowheads) because of lymphomatous infiltration of the trigeminal nerves. Increased enhancement of the temporalis muscles bilaterally (T) is related to denervation change from involvement of V₃. D, A slightly more superior postgadolinium axial T₁-weighted image with fat saturation demonstrates abnormal thickening and enhancement of the cisternal segments of the trigeminal nerves bilaterally, also caused by lymphomatous infiltration. E, An axial fast spin-echo T₂-weighted image demonstrates a large mass involving the right maxillary sinus, right nasal cavity, and right ethmoid air cells. Fat suppression was not used in this case. F, An axial diffusion-weighted image (same patient as in Fig. 17-2E) shows marked hyperintensity of the lesion. This image contains both T₂-weighted and diffusion-weighted information. G, The apparent diffusion coefficient map at the same level as Fig. 17-2F represents the diffusion-weighted image with the T₂ contribution removed and it therefore represents “true” diffusion information, with reduced diffusion demonstrated as low signal intensity in the mass. This is consistent with high cellularity, as is often seen in small, round, blue-cell tumors. In this case, biopsy confirmed sinonasal rhabdomyosarcoma.

Additional planes may be useful in some circumstances (e.g., coronal FSE T₂-weighted images with fat saturation for paranasal sinus pathologic conditions). Additional sequences such as magnetic resonance angiography may also be useful in certain circumstances (e.g., paragangliomas), but are not necessary for evaluation of most neoplasms of the head and neck. Modalities in widespread use in the brain (magnetic resonance spectroscopy, diffusion-weighted imaging, functional MRI) have not yet found a place in routine head and neck imaging. There is growing interest in diffusion-weighted imaging in the head and neck, however, because the relative reduction in water diffusion that is seen in highly cellular neoplasms can be useful in the differential diagnosis and staging of primary tumors and the detection of residual or recurrent disease following primary therapy (Fig. 17-2E to Fig. 17-2G).⁶

As mentioned earlier, in many cases MRI is preferred to CT because of its superior soft-tissue contrast and increased sensitivity to processes such as perineural spread of tumor. It is important for the clinician to be aware of MRI safety considerations, however, and relative and absolute contraindications to MRI.^7,8 It is also important to be aware of the entity of nephrogenic systemic fibrosis (NSF), a scleroderma-like condition that primarily involves the skin but may also affect organs such as the liver, lung, heart, and muscle. Current thinking suggests an association and a potential causal link between the use of gadolinium-based contrast agents and the development of NSF among patients with advanced kidney disease; hence it is important to screen for kidney disease prior to administration of gadolinium-based contrast agents for MR scanning.⁹

Positron Emission Tomography

PET offers information regarding tissue metabolism rather than simply demonstrating anatomy. The most common radiopharmaceutical in use for cancer imaging at present is ¹⁸F-fluorodeoxyglucose (FDG). This is taken up into tissues in proportion to the glycolytic rate, which is generally increased in neoplastic processes. FDG does accumulate in some normal structures to a variable degree (sublingual glands, lymphoid tissue of Waldeyer ring) (Fig. 17-3),¹⁰ and may also accumulate in active muscles (e.g., the larynx if a patient has been talking) and brown fat (which is often present in the supraclavicular fossae). The current widespread availability of PET-CT scanning allows far more precise localization of FDG activity and more precise interpretation than was previously possible with FDG PET scanning alone, and allows pitfalls (such as interpreting vascular, muscular, or brown fat activity as neoplasia) to be avoided.^11,12 Situations in which FDG PET-CT scanning is particularly helpful include the search for an unknown primary lesion in a patient presenting with metastatic neck disease (Fig. 17-4A), the assessment of residual or recurrent disease following primary therapy, and the search for synchronous or metachronous primary lesions or distant metastases (Fig. 17-4B and Fig. 17-4C).^13,14 FDG PET-CT scanning is also useful for staging the neck. There may be a significant number of false-negative studies in patients with clinically N₀ necks, however, as small tumor deposits (on the order of 1 to 4 mm) may not be detectable on FDG PET-CT scan, but will be found if a neck dissection is performed. It must also be remembered that FDG is a nonspecific tracer that is concentrated in areas of inflammation as well as neoplasia. An FDG PET-CT scan must therefore always be interpreted in appropriate clinical context and must be supplemented with tissue sampling and follow-up imaging as appropriate.

Spatial Anatomy of the Head and Neck

The spaces of the suprahyoid neck are defined by the three layers of the deep cervical fascia (the superficial, middle, and deep layers). The spaces so defined include the pharyngeal mucosal space, parapharyngeal space, masticator space, parotid space, carotid space, retropharyngeal space, and perivertebral space. These spaces are demonstrated in Fig. 17-5. In a discussion of head and neck cancer, however, which is dominated by SCC of the mucosa of the upper aerodigestive tract, we discuss lesions arising in the nasopharynx, oropharynx, oral cavity, hypopharynx, and larynx. The infrahyoid neck has traditionally been taught from the point of view of surgical triangles, but can also be described as a series of spaces, which facilitates understanding and interpretation of cross-sectional imaging modalities such as CT and MRI. The spaces of the infrahyoid neck are also defined by the three layers of the deep cervical fascia and include the superficial space (external to the superficial layer of the deep cervical fascia), visceral space (including the thyroid gland, larynx, and esophagus), carotid space, retropharyngeal space, and prevertebral space. These spaces are demonstrated in Fig. 17-6.

FIGURE 17-5 • Diagram of the spatial anatomy of the suprahyoid neck at the midnasopharyngeal level. The spaces are defined by the three layers of the deep cervical fascia: superficial layer (solid line), middle layer (blue dashed line), and deep layer (dashed line). In addition, the pharyngobasilar fascia, which connects the superior constrictor muscle to the skull base, is shown as a dark curvilinear line superficial to the middle layer of the deep cervical fascia. The spaces include the pharyngeal mucosal space (PMS), retropharyngeal space (RPS), parapharyngeal space (PPS), carotid space (CS), parotid space (PS), masticator space (MS), and perivertebral space (PVS). The buccal space (BS) is not a true fascia-defined compartment.

(Modified from Harnsberger HR: CT and MRI of masses of the deep face. Curr Probl Diagn Radiol 16:141, 1987.)

FIGURE 17-6 • Diagram of the spatial anatomy of the infrahyoid neck at the midthyroid level. The spaces are again defined by the three layers of the deep cervical fascia. The superficial layer encircles the neck completely, splitting to encircle the sternocleidomastoid and trapezius muscles. External to this layer is the superficial space of the infrahyoid neck. The middle layer encircles and defines the visceral space, which includes the trachea, esophagus, and thyroid gland. The deep layer of fascia defines the perivertebral space, which includes the prevertebral space proper and the paraspinal portion of the prevertebral space. The carotid space is defined by contributions from all three fascial layers. The posterior cervical space is largely fat-filled and contains multiple lymph nodes.

(Modified from Smoker WR, Harnsberger HR: Differential diagnosis of head and neck lesions based on their space of origin. 2. The infrahyoid portion of the neck. AJR Am J Roentgenol 157:155, 1991.)

Nasopharynx

Normal Anatomy

The nasopharynx is bounded anteriorly by the posterior nasal cavity at the level of the choana; superiorly by the sphenoid sinus; posterosuperiorly by the clivus, upper cervical spine, and prevertebral muscles; and inferiorly by the soft palate. Its contents include squamous mucosa, lymphoid tissue (adenoids), pharyngeal constrictor muscles, the levator palatini muscle, and the torus tubarius (the projecting posterior lip of the pharyngeal opening of the eustachian tube). Because of the location of the pharyngeal opening of the eustachian tube, nasopharyngeal masses often obstruct the eustachian tube, causing dysfunction and serous otitis. The Rosenmüller fossa represents the uppermost aspect of the lateral recess of the nasopharynx and is a common site of origin of nasopharyngeal cancers. The normal nasopharynx is shown in Fig. 17-7.

FIGURE 17-7 • Axial T₁-weighted image of the normal nasopharynx. Nasopharyngeal airway (NP), longus colli muscle (LC), clivus (C), torus tubarius (T), hypoglossal canal (H), internal jugular vein (J), internal carotid artery (white arrowhead), medulla (M), and cerebellum (Cb) are indicated. The straight white arrow indicates air in the right lateral pharyngeal recess (Rosenmüller fossa); on the left, the mucosal surfaces of the fossa are coapted (white dots). The eustachian tube orifice is just anterior to the torus tubarius on either side.

Pathologic Conditions

Nasopharyngeal carcinoma (NPC) is the most common malignant lesion of the nasopharynx. NPC may be small and confined to the Rosenmüller fossa or large with extension to the skull base, intracranial structures, and deep spaces of the head and neck.¹⁸ Lymphadenopathy is often a prominent feature of even early NPC. NPCs most commonly metastasize to retropharyngeal, level-II, and level-V nodes. Contralateral nodes are also at significant risk because of rich bilateral lymphatic drainage, and nodal imaging should extend from the high retropharyngeal level to the supraclavicular fossa. Note that the imaging appearance of normal and abnormal lymph nodes and the classification of lymph nodes based on anatomic “levels” is discussed later in the “Lymph Nodes” section of this chapter.

NPC generally presents as an asymmetric, infiltrative mass with a variably exophytic component that is intermediate in signal intensity on both T₁– and T₂-weighted images and shows homogeneous enhancement postgadolinium (Fig. 17-8). Small lesions are typically limited by the surrounding pharyngobasilar fascia; once this barrier is breached, the tumor may directly invade the adjacent fatty parapharyngeal space. NPC may also extend directly to the skull base: superiorly or superolaterally to the floor of the sphenoid sinus, pterygoid process, or foramen lacerum, or posteriorly to the clivus. Skull-base involvement is best detected on T₁-weighted images, which show loss of the normal bright signal of marrow fat (Fig. 17-9). The sinus of Morgagni, which allows passage of the cartilaginous portion of the eustachian tube and the levator veli palatini muscle from the skull base to the pharynx, is a natural defect that may allow extension of NPC laterally into the parapharyngeal space and carotid space. NPC may then involve V₃ and extend intracranially via the foramen ovale to the Meckel cave. Cavernous sinus extension and perineural spread of disease (usually along V₃) are often best demonstrated on postgadolinium T₁-weighted images with fat saturation (Fig. 17-10).

FIGURE 17-8 • A, Axial fast spin-echo T₂-weighted image with fat saturation through the nasopharynx in a patient who presented with a neck mass (not shown). The right Rosenmüller fossa is expanded by an intermediate-signal-intensity, soft-tissue mass that also infiltrates along the mucosa overlying the torus tubarius and toward the midline (arrowheads). Biopsy-proven nasopharyngeal carcinoma. Also indicated are the longus colli (LC), lateral pterygoid (LP), masseter (M) muscles, and medulla (Me). B, Axial postgadolinium T₁-weighted image with fat saturation shows moderate homogeneous enhancement of the mass. Also labeled are the clivus (C), internal jugular vein (IJV), and mastoid (Ma).

FIGURE 17-9 • Sagittal T₁-weighted image in a patient with nasopharyngeal carcinoma shows loss of the normal high signal intensity in the clivus (*) and replacement by infiltrative tumor. The tumor (T) is also seen in the nasopharynx and involving the retro-clival dura. Clival involvement can be easily missed on a computed tomography scan if there is no gross bone erosion. Also shown are the pituitary gland (P), C2 vertebral body (C2), and the soft palate (SP).

FIGURE 17-10 • A, Axial postgadolinium T₁-weighted image with fat saturation in a patient with recurrent nasopharyngeal carcinoma and left trigeminal nerve motor and sensory symptoms demonstrates intracranial extension of tumor to the left cavernous sinus (large white arrow) and also involvement of the left foramen rotundum (white arrowhead). There is abnormal enhancement of the dura of the left middle cranial fossa (small black arrows), as well as of the greater wing of the sphenoid, resulting from tumor infiltration. Denervation change with asymmetrical enhancement is seen in the left temporalis muscle (T). A small focus of brain parenchymal enhancement (small white arrow) is caused by radiation necrosis from prior therapy. Also indicated are the right cavernous carotid artery (C), the pons, and the temporal lobe. B, Coronal postgadolinium T₁-weighted image with fat saturation in the same patient demonstrates fluid signal intensity in the normal right Meckel cave (white arrow), as well as normal suppressed marrow fat in the right greater wing of the sphenoid (white S). On the symptomatic left side, the Meckel cave (white arrowheads) is expanded and the expected fluid has been replaced by infiltrative tumor. Abnormal signal intensity is seen in the tumor-involved sphenoid wing (black S). C, A slightly more anterior coronal postgadolinium T₁-weighted image with fat saturation shows normal foramen ovale (O) and V₃ (white arrows) on the right, as well as normal intermediate signal intensity of the medial (MP) and lateral (LP) pterygoid muscles. On the left, tumor has invaded laterally through the pharyngobasilar fascia and has extended intracranially along V₃, with abnormal enhancing soft tissue seen in the left cavernous sinus, the Meckel cave, and dura (black arrows). Infiltrating tumor has obscured normal anatomy, and it is difficult to separate V₃ from the surrounding tumor-infiltrated soft tissues. The cavernous carotid arteries are indicated (C). Denervation change is present in the muscles of mastication resulting from tumor invasion of V₃, and this manifests as abnormal enhancement of the left medial and lateral pterygoid muscles (MP, LP) as compared with the right.

Oropharynx

Normal Anatomy

The oropharynx is bounded anteriorly by the circumvallate papillae of the tongue and the anterior tonsillar pillars; these structures separate the oropharynx from the oral cavity.¹⁹ Posteriorly it is bounded by the pharyngeal constrictor muscles and superiorly by the soft palate. Inferiorly it is separated from the larynx by the epiglottis and glossoepiglottic fold and from the hypopharynx by the pharyngoepiglottic fold. Its contents include the tongue base, palatine tonsils, soft palate, and oropharyngeal mucosa and constrictor muscles from the level of the palate to the hyoid bone. The normal oropharynx is shown in Fig. 17-11.

FIGURE 17-11 • A, Sagittal T₁-weighted image shows the oropharynx (OP) extending from the level of the soft palate (U) superiorly to the level of the bottom of the vallecula (V) inferiorly. Also shown are the normal nasopharyngeal soft tissues (NP), the clivus (C), the C2 vertebral body, and the epiglottis (white arrow). B, Axial fast spin-echo T₂-weighted image with fat saturation of the normal oropharynx shows the uvula (U), base of tongue (BOT), and palatine tonsils (T). Also shown are the spinal cord (SC), C2 vertebral body, medial pterygoid (MP) and masseter (M) muscles, and the parotid gland (C).

Pathologic Conditions

SCC accounts for most tumors of the oropharynx, followed by lymphoma, minor salivary gland lesions, and mesenchymal tumors.²⁰ The appearance of SCC varies somewhat with the specific subsite involved, and the tumor may be variably exophytic or deeply infiltrative. Tumors of the tonsillar fossa may be occult when small and may present with cervical nodal disease. Tonsil cancers most commonly metastasize to level-II lymph nodes. Larger tumors of the tonsillar fossa may spread anteriorly or posteriorly to involve the tonsillar pillars or anteriorly to invade the tongue. They may extend deeply to invade the constrictor muscles and then gain access to the parapharyngeal space and skull base.

Tumors of the base of the tongue, when small, may be difficult to separate from normal lingual tonsillar tissue. Malignancy of the tongue base is usually asymmetrical, crossing midline only when large. Patterns of spread include posterolaterally to the tonsillar pillar and pharyngeal wall, submucosally into the supraglottic larynx, or anteriorly into the floor of the mouth. Nodal metastases are common with base-of-tongue tumors, with level-II nodes most commonly involved, followed by level-III nodes. Contralateral level-II nodes are also commonly involved. The imaging features of lymphomas and minor salivary tumors are similar to SCC, and clinical examination and tissue sampling are necessary to make a specific diagnosis in most cases. Representative tonsillar fossa and base of tongue lesions are shown in Fig. 17-12 and Fig. 17-13.

FIGURE 17-12 • A, Axial fast spin-echo T₂-weighted image with fat saturation in a patient with squamous cell carcinoma demonstrates a large mass in the left tonsillar fossa (arrowheads), extending into the soft palate (SP). The mass abuts but does not invade the mandible (M) and the base of tongue. B, Postgadolinium, the mass demonstrates moderate homogeneous enhancement.

FIGURE 17-13 • A, Sagittal T₁-weighted image shows an exophytic soft tissue mass (T) arising from the base of tongue (BOT) in this patient with squamous cell carcinoma of the base of the tongue. The uvula (U) is shown above. No significant invasion into the oral tongue or floor of mouth is noted in this largely exophytic lesion. B, Axial fast spin-echo T₂-weighted image with fat saturation demonstrates the intermediate-signal-intensity primary mass lesion (T), as well as bilateral heterogeneous, level-IIA metastatic lymph nodes (arrows).

Oral Cavity

Normal Anatomy

The oral cavity lies anterior to the oropharynx and is separated from it by the circumvallate papillae; soft palate; and anterior tonsillar pillars, which make up its posterior boundary.²¹ The oral cavity is bounded superiorly by the hard palate, laterally by the cheek, and inferiorly by the mylohyoid muscle. In addition to the mucosal area of the oral cavity (the dominant structure of which is the oral tongue), the mylohyoid muscle cleaves the lower oral cavity into the sublingual and submandibular spaces (Fig. 17-14). The sublingual space is frequently invaded by tumors of the floor of the mouth. The submandibular space is most commonly involved by inflammatory processes or metastases to level-I lymph nodes. Direct extension to the submandibular space by SCC of the oral cavity is uncommon.

FIGURE 17-14 • A, Sagittal T₁-weighted image of the oral cavity. Well seen are the longitudinal (L) and transverse (T) muscle fibers of the tongue, as well as the genioglossus (GG) and geniohyoid (GH) muscles. Also indicated are the genu of the mandible (M), the hyoid bone (H), the nasopharyngeal (NP) and oropharyngeal (OP) airways, and the normal clivus (C) showing fatty signal intensity in the clival marrow. B, Coronal T₁-weighted image of the oral cavity shows the mylohyoid muscle (), forming the U-shaped muscular floor of the mouth and separating the sublingual space above (SLS) from the submandibular space below (SMS). The midline fatty lingual septum is indicated by the white arrowhead. Also shown are the masseter (M) and temporalis (T) muscles, the inferior turbinate (IT), and the nasal septum (S).

Pathologic Conditions

All surfaces of the oral cavity are covered by squamous mucosa, so there are many potential sites of origin of SCC. In addition, numerous minor salivary glands are distributed subepithelially throughout the oral cavity and can give rise to benign or malignant salivary tumors. SCC of the oral tongue, floor of the mouth, and gingivobuccal surfaces is well assessed by clinical examination. In cases of small or superficial lesions, imaging may be normal even though direct inspection clearly demonstrates a neoplasm. CT and MRI are most useful for assessing deep extension of malignant processes, involvement of critical structures such as the neurovascular bundle, and the presence of associated pathologic lymphadenopathy. They are also useful for presurgical and radiotherapy planning. Representative cases are illustrated in Fig. 17-15 and Fig. 17-16. Because mucosal surfaces are usually coapted during scanning, which limits sensitivity for small lesions and subtle deep invasion, it may be useful to have the patient perform a “puffed-cheek” maneuver²² to improve the assessment of oral cavity cancers, especially those of the buccal mucosa (Fig. 17-17). Cancers of the oral tongue most commonly metastasize to ipsilateral level-II lymph nodes, followed by level-I nodes, whereas cancers of the floor of the mouth most commonly metastasize to level-I nodes followed by level-II nodes.

FIGURE 17-15 • A, Contrast-enhanced computed tomography scan in a patient with an ulcerative lesion of the left lateral tongue is significantly limited by dental artifact but does show a subtle mass in the left oral tongue (white arrows). Also indicated are the masseter muscle (M), parotid gland (P), and right internal carotid artery (black arrow). B, Axial T₁-weighted magnetic resonance image in the same patient nicely demonstrates an infiltrative mass (arrow) in the left hemitongue that does not extend to the midline lingual septum (arrowheads). A biopsy confirmed squamous cell carcinoma.

FIGURE 17-16 • Axial postgadolinium T₁-weighted image with fat saturation in a patient with squamous cell carcinoma of the floor of the mouth. The lesion has extended into and extensively infiltrates the right sublingual gland/space (arrowheads). The normal left sublingual gland is shown for comparison (SL).

FIGURE 17-17 • Axial postgadolinium T₁-weighted image in a patient with buccal carcinoma, performed using the puffed-cheek technique. Note the air between the buccal mucosa and the mandible. The right-sided carcinoma (black arrows), which infiltrates the underlying buccinator muscle, is well seen as compared with the normal left side.

Hypopharynx

Normal Anatomy

The hypopharynx extends from the level of the hyoid bone and valleculae to the cricopharyngeus (or inferior margin of the cricoid cartilage on imaging studies). Its three major anatomic subsites include the pyriform sinus, postcricoid area, and posterior pharyngeal wall. The pyriform sinus is shaped like an inverted pyramid, with its apex at the level of the cricoarytenoid joint. The postcricoid area extends from the level of the arytenoid cartilages to the inferior border of the cricoid cartilage and is the anterior wall of the lower pharynx. The posterior hypopharyngeal wall extends from the level of the vallecula to the level of the cricoarytenoid joints (Fig. 17-18).

FIGURE 17-18 • A, A sagittal T₁-weighted image demonstrates the superior to inferior extent of the hypopharynx (white lines), from the bottom of the vallecula (V) to the bottom of the cricoid cartilage. Also shown are the clivus (C), uvula (U), C₂ vertebral body (C₂), epiglottis (E), hyoid bone (H), trachea (T), and fat in the pre-epiglottic space (PES). B, Axial T₁-weighted image demonstrates the normal aryepiglottic folds (*) and pyriform sinus (PS), as well as the sternocleidomastoid muscle (SCM) and internal jugular vein (IJV). C, Coronal T₁-weighted image demonstrates the epiglottis (E) and pyriform sinuses (PS). Also shown are the soft palate (SP) and uvula (U), the palatine tonsil (T), the medial (MP) and lateral pterygoid (LP) muscles, the masseter muscle (M), and the submandibular gland (SMG).

Pathologic Conditions

The contents of the hypopharynx include squamous mucosal surfaces, minor salivary glands, and inferior pharyngeal constrictor muscles. SCC is the most common hypopharyngeal pathologic condition.²³ The pyriform sinus is the hypopharyngeal subsite most commonly involved with SCC (Fig. 17-19). SCC arising in this location tends to invade the soft tissues of the neck early and is frequently accompanied by pathologic lymphadenopathy. Ipsilateral metastatic nodes are common in both levels II and III. The extensive submucosal growth of hypopharyngeal tumors and invasion of adjacent organs are often not apparent on clinical examination, but are readily detected on cross-sectional imaging (Fig. 17-20). The sagittal plane is particularly useful in assessing the superoinferior extent of lesions of the posterior pharyngeal wall (Fig. 17-21), but the exact boundary of inferior extension into the cervical esophagus is often difficult to define by imaging and must be assessed endoscopically.

FIGURE 17-19 • Axial T₁-weighted image in a patient who presented with a large nodal mass resulting from metastatic squamous cell carcinoma demonstrates a relatively small primary tumor in the left pyriform sinus (arrowheads). The normal right pyriform sinus (PS) is shown for comparison. Also shown are the common carotid arteries (C), the right internal jugular vein (J) (note that the left internal jugular vein is severely compressed or occluded by mass effect and is not visible), fat in the pre-epiglottic space (PES), and the sternocleidomastoid muscle (SCM).

FIGURE 17-20 • Axial fast spin-echo T₂-weighted image with fat saturation from a patient with a large hypopharyngeal mass (asterisks) that involves the postcricoid region and extends into the cervical esophagus, invades the thyroid gland (the normal right thyroid, is shown for comparison), erodes the left thyroid cartilage (TC), and infiltrates the cricoid cartilage. Tumor also extends through the cricothyroid joint, and the left vocal cord (VC) is enlarged and edematous because of acute denervation change. The common carotid arteries (C) and internal jugular veins (J) are indicated.

FIGURE 17-21 • Sagittal T₁-weighted image demonstrates a large hypopharyngeal mass, growing exophytically from the posterior pharyngeal wall. The inferior extent of the lesion into the cervical esophagus is not clear from imaging alone and must be correlated with endoscopic visualization.

Larynx

Normal Anatomy

The larynx is an anatomically complex region that consists of a mucosal covering draped over a supporting cartilaginous skeleton made up of the cricoid, thyroid, and arytenoid cartilages.²⁴ Structures that are part of the larynx include the epiglottis, aryepiglottic folds, and true and false vocal cords. Between the mucosal surfaces and the cartilaginous skeleton lie the predominantly fat-filled pre-epiglottic and paraglottic spaces. The endolarynx is usually divided into three segments (Fig. 17-22 and Fig. 17-23). The supraglottis extends from the tip of the epiglottis above to the laryngeal ventricles below and includes the epiglottis, aryepiglottic folds, pre-epiglottic space, false vocal cords, arytenoid cartilages, and the paraglottic (paralaryngeal) space. The glottis includes the true vocal cords and both the anterior and posterior commissures. On a normal axial CT scan or MRI, less than 1 mm of tissue should be discernible at the level of the commissures. The subglottic area extends from the undersurface of the true vocal cords above to the inferior aspect of the cricoid cartilage. As the mucosal surface of the subglottic area is closely applied to the cricoid cartilage, any tissue seen on the airway side of the subglottic larynx should be viewed with suspicion.

FIGURE 17-22 • A series of axial contrast–enhanced computed tomography scans through the larynx, from cephalad to caudad. A, Indicated are the free edge of the epiglottis (E), the vallecula (V), lingual tonsillar tissue (LT) at the base of the tongue, submandibular gland (SMG), sternocleidomastoid muscle (SCM), common carotid artery (C), and internal jugular vein (IJV). The white arrowheads indicate normal level-II lymph nodes. B, Image through the high supraglottic level shows the pyriform sinus (PS) and aryepiglottic fold (white arrowhead), fat in the pre-epiglottic space (PES), and the superior cornu of the thyroid cartilage (black arrowhead). The strap muscles (SM) are indicated. C, Image through the low supraglottic level shows the midline thyroid notch (N) in the thyroid lamina, the false vocal cords (white arrowheads), and the fat-filled paralaryngeal space (P). Ossified segments of the thyroid cartilage are indicated (black arrowheads). D, Image through the glottic level shows the true vocal cord (VC), the thin anterior commissure (white arrowhead), and the arytenoid (A) and cricoid (C) cartilages. The calcified but not ossified thyroid lamina is indicated (black arrowheads), as is the top of the thyroid gland (T). E, Image through the subglottic larynx shows the cricoid cartilage (C), the inferior cornua of the thyroid cartilage (black arrowheads), and the cricothyroid membrane (white arrowheads). The cricopharyngeus muscle/proximal cervical esophagus is also indicated (CPM/CE). The x indicates the expected position of the right recurrent laryngeal nerve, which runs in the tracheoesophageal groove and at this level is immediately adjacent to the cricothyroid joint.

FIGURE 17-23 • A, Sagittal T₁-weighted image through the normal larynx. The free margin (E) and fixed portion (E*) of the epiglottis are shown, as is the fat-filled pre-epiglottic space (P), the laryngeal ventricle (white arrow), the true vocal cord (VC), and the arytenoid (A) and cricoid (C) cartilages. The hyoid bone (H), genu of the mandible (G), and geniohyoid muscle (GH) are also shown. The supraglottis extends from the tip of the epiglottis above to the laryngeal ventricles below, the glottis includes the true vocal cords and the anterior and posterior commissures, and the subglottis extends from the undersurface of the true cords to the inferior surface of the cricoid cartilage. B, Coronal T₁-weighted image through the normal larynx. The glottic level (G), laryngeal ventricle (•), subglottis (SG), body of the hyoid bone (H) and trachea (T) are indicated. The white arrow traverses the vocalis muscle and points to the edge of the true vocal cord, and the black arrow traverses the paralaryngeal fat and points to the false vocal cord.

The site of origin of SCC within the larynx dictates the likelihood of accompanying metastatic nodal involvement. The supraglottic larynx has a rich network of draining lymphatics and therefore a propensity toward metastatic nodal disease, whereas cancers of the glottic and subglottic larynx are less likely to be associated with nodal metastases. Ipsilateral level-II and level-III metastatic nodes are present in 50% to 70% of supraglottic cancers, and contralateral level-II and level-III nodes are seen in 10% to 20% of cases.^25,26 Glottic cancers have a lower incidence of ipsilateral nodal metastases and a far lower incidence of contralateral nodal metastases.

The larynx is a site in which CT may be superior to MRI for assessing the extent of a primary tumor. Although MRI has superior soft tissue contrast and superior sensitivity for cartilage invasion, it is often severely limited by motion caused by breathing, coughing, and swallowing. Spiral and multislice CT scanners allow the rapid acquisition of images, often in a single breath hold, and facilitate high-quality, multiplanar reformations of the larynx.

Pathologic Conditions

The vast majority of laryngeal neoplasms are SCCs. These tumors are usually well assessed by laryngoscopy, but imaging is useful for the assessment of submucosal and deep extension. The imaging of each laryngeal subsite raises certain unique issues. Supraglottic lesions (Fig. 17-24) are often large at the time of diagnosis because there is no accompanying hoarseness until the true vocal cord is involved; nodal metastases are common at presentation. Anterior supraglottic lesions (those involving the epiglottis) spread initially into the pre-epiglottic space, and later may access the tongue base above and the paraglottic space below. The pre-epiglottic space is optimally viewed on a sagittal T₁-weighted image, which is very sensitive to infiltration of the normally bright pre-epiglottic fat by intermediate-signal-intensity tumor. Posterolateral supraglottic cancers (aryepiglottic fold, false vocal cord, laryngeal ventricle) may grow exophytically off the aryepiglottic folds or spread submucosally into the paraglottic space from the false cords and ventricle. Glottic SCCs often present early with voice change or hoarseness, and T₁ lesions may not be visible on cross-sectional imaging studies. More advanced lesions are imaged to assess paraglottic and subglottic extension, as well as cartilage involvement (Fig. 17-25). Particular attention should be paid to the anterior and posterior commissures, which require thin-section technique. The subglottis is relatively easy to assess, as the area below the undersurface of the true cord has no normal tissue between the mucosal surface and the cricoid cartilage, so any soft-tissue thickening represents a pathologic condition (Fig. 17-26).

FIGURE 17-24 • A and B, Axial postgadolinium T₁-weighted images with fat saturation in a patient with a small supraglottic cancer who presented with a neck mass and mild dysphagia. Indicated are the primary tumor, which infiltrates and thickens the free margin of the epiglottis (white arrowheads), as well as a metastatic level-IIA lymph node (LN). Also shown are the lingual tonsils (LT), the glossoepiglottic fold (white arrow), the submandibular gland (SMG) and the sternocleidomastoid muscle (SCM). C and D, Axial images from a postcontrast computed tomography scan in a patient with a massive supraglottic cancer who presented with dysphagia, odynophagia, and cachexia. Indicated is the primary tumor (white arrowheads), which infiltrates and thickens the epiglottis and aryepiglottic folds. There is extensive infiltration of the pre-epiglottic fat, with a tumor abutting the posterior aspect of the hyoid bone (H) and only a thin sliver of preserved hypodense pre-epiglottic fat seen on the left (black arrows).

FIGURE 17-25 • Axial T₁-weighted images in a patient with squamous cell carcinoma of the glottic larynx. A, A large mass infiltrates the left true vocal cord and involves the anterior commissure. The left thyroid (T) and arytenoid (A) cartilages have abnormal signal intensity and are infiltrated by the tumor, whereas the right thyroid and arytenoid cartilages are ossified and have normal fatty signal intensity. The mass markedly widens the left cricothyroid joint (xx). B, A more inferior image shows extension of the tumor submucosally in the left true vocal cord and anterior commissure, with extension across midline to involve the right true vocal cord. Involvement of the left thyroid cartilage (T) is clear when its low signal intensity is compared with the normal high signal intensity in the right thyroid cartilage.

FIGURE 17-26 • Axial contrast-enhanced computed tomography scan in a patient with squamous cell carcinoma of the subglottis demonstrates abnormal focal thickening of the mucosal surface (white arrow) by the soft tissue mass. The cricoid cartilage (C) is adjacent to the tumor, but not clearly involved by it. Normally the air column should appear to directly contact the anterior surface of the cricoid, as in FIGURE 17-22E. The thyroid cartilage is also indicated (T).

The laryngeal cartilages normally calcify with age, and eventually ossify. Assessing involvement of the laryngeal cartilages by tumor is an important part of the radiologic evaluation of SCC of the larynx.^27,28 CT can be used to assess asymmetric sclerosis and gross destruction, whereas MRI is better suited to assess replacement of normal tissue by an infiltrating tumor. Both modalities are limited by their inability to separate tumor involvement from reactive changes, and the only sure indicators of neoplastic involvement are gross cartilage destruction or the presence of a tumor on both sides of the cartilaginous structure. Multiple studies have demonstrated that the radiologic ability to conclusively demonstrate cartilage involvement by tumor (except with gross destruction or tumor on both sides of the cartilage) is limited. Ongoing advances in CT and MRI should help to improve the detection of more subtle cartilage involvement by tumor.

Lymph Nodes

Assessment of the cervical lymph nodes for metastatic involvement is an important part of the evaluation of the patient with head and neck cancer. Lymph nodes are seen on all cross-sectional studies of the head and neck. Lymph nodes have historically been described using anatomy-based terminology (e.g., jugulodigastric, spinal accessory), but have more recently been described using nodal “levels” that group nodes on the basis of clinical and pathophysiologic information (Fig. 17-27). These nodal levels have been translated to cross-sectional imaging,^29,30 and this imaging-based classification is summarized in Table 17-1 and illustrated in Fig. 17-28. On imaging studies, normal nodes are usually less than 10 mm in short-axis diameter. They show intermediate density on CT, scans and on MRI show homogeneous intermediate signal intensity on T₁-weighted images, mild hyperintensity on T₂-weighted images, and homogeneous enhancement postgadolinium (Fig. 17-29). Metastatic deposits often lead to nodal heterogeneity. Areas of cystic degeneration, keratin pools, or frank necrosis result in nodal heterogeneity (typically seen as variable areas of high and/or low signal intensity on T₂-weighted images or focal lack of enhancement on postgadolinium T₁-weighted images) that is considered to represent neoplastic involvement in a patient who has head and neck cancer (Fig. 17-30A; also as shown in Fig. 17-13B). Abnormal nodes may also show extracapsular spread of the tumor, manifest as irregular margination and invasion of adjacent fat or other structures (Figs. 17-30B and 17-30C). Of particular interest is extension of nodal disease to involve the carotid artery. The imaging assessment of carotid invasion is difficult. In general, a carotid artery that is contacted by tumor over 270 degrees or more of its circumference is likely invaded, but actual adventitial involvement may need to be assessed intraoperatively.

Table 17-1 Summary of Imaging-Based Nodal Classification

Normal Anatomy

The thyroid gland lies within the visceral space of the infrahyoid neck, wrapping around the upper trachea. It usually consists of a right and a left lobe, connected across the midline by the thyroid isthmus. In at least 50% of patients, a pyramidal lobe may be seen extending superiorly from the isthmus along the course of the thyroglossal duct in the neck. The thyroid gland is highly vascular and is divided by multiple fibrous septae.

The normal thyroid gland is intrinsically dense on CT because of its iodine content and enhances intensely and homogeneously following administration of iodinated contrast (Fig. 17-49). In a patient suspected of having or known to have thyroid carcinoma, administration of iodinated contrast should be avoided if the patient is to undergo radioiodine imaging or therapy, because the iodine from the contrast material will saturate the gland for weeks to months. These patients are usually best assessed by MRI, which provides exquisite detail of the extent of disease and avoids the administration of an iodine-based contrast agent. On MRI, the normal thyroid gland is of homogeneous intermediate signal intensity on T₁– and T₂-weighted images and shows intense and homogeneous enhancement postgadolinium.⁴⁷

FIGURE 17-49 • A, Axial noncontrast computed tomography (CT) scan demonstrates the intrinsic high density of the normal thyroid gland (T) because of its high iodine content. Also shown are the trachea (Tr), esophagus (E), sternocleidomastoid muscle (SCM), common carotid artery (C), and internal jugular vein (J). The scan also demonstrates the difficulty of distinguishing vessels from other structures on noncontrast examination. B, Axial contrast-enhanced CT scan through the lower neck shows homogeneous enhancement of the thyroid gland. The narrow thyroid isthmus (arrowheads) is seen connecting the right and left lobes of the thyroid.

Pathologic Conditions

Unlike other tumors of the head and neck, which are primarily assessed by CT and MRI, pathologic conditions of the thyroid are often initially addressed by US and nuclear medicine studies using radiolabeled iodine. Cross-sectional imaging with CT or MRI is used secondarily to evaluate the deep-tissue extent of a mass that is to be surgically removed, or for the assessment of nodal metastases or chest disease. In many cases a thyroid lesion is picked up incidentally on a cross-sectional imaging study ordered for another purpose, but most of these lesions prove to be colloid cysts or adenomas rather than thyroid malignancies.

A thyroid malignancy may simulate a benign process on cross-sectional imaging, and tissue sampling is usually necessary for definitive diagnosis. Both papillary and follicular carcinomas of the thyroid may present as well-circumscribed lesions that have variable enhancement characteristics on CT or MRI. Cyst formation may result in well-circumscribed areas of fluid density or intensity, and calcifications may be seen as well. On US, neoplasms are typically hypoechoic, and on radioiodine studies they are seen as cold nodules. If a lesion is allowed to grow unchecked, invasion into adjacent structures will be seen, and airway compromise may be seen as well (Fig. 17-50). In addition, cervical nodal metastatic disease may be evident. On MRI, the presence of intrinsic T₁ shortening in lymph nodes is highly suspicious for metastatic thyroid cancer (Fig. 17-51) resulting from either the thyroglobulin content or the propensity of these nodes to undergo hemorrhage. On CT, nodes involved with metastatic thyroid cancer may appear cystic.

FIGURE 17-50 • Coronal T₁-weighted image in a young man presenting with a neck mass and stridor demonstrates a huge soft-tissue mass (arrowheads) involving the right lower neck, compressing the trachea (white dot) and extending into the superior mediastinum. The mass is highly vascular, as evidenced by multiple serpiginous hypointense structures that represent flow voids. The lung, right atrium (RA), and right ventricle (RV) are shown. Tissue sampling confirmed follicular carcinoma of the thyroid.

FIGURE 17-51 • Magnetic resonance images of the neck in a young woman who has neglected a long-standing, progressively enlarging neck mass. A, Axial T₁-weighted image demonstrates enlargement and heterogeneity of the right and left lobes of the thyroid. The trachea (T), common carotid arteries (C), and right internal jugular vein (J) are shown for orientation. Also demonstrated is a large, heterogeneous, mostly hyperintense mass (black arrows) consistent with a metastatic nodal mass. The high signal intensity of the nodes on a pregadolinium T₁-weighted image is highly suggestive of metastatic thyroid cancer. Lymph nodes involved by metastatic melanoma may also demonstrate high signal intensity on T₁-weighted images. B, Axial fast spin-echo T₂-weighted image with fat saturation demonstrates papillary frondlike solid elements of the tumor (black arrows) as well as fluid-fluid levels (black arrowheads) consistent with hemorrhage into partly cystic lymph nodes. C, Postgadolinium T₁-weighted image with fat saturation shows heterogeneous enhancement of the solid areas of the tumor. Tissue sampling confirmed papillary carcinoma of the thyroid.

More aggressive thyroid cancers, notably anaplastic thyroid cancer, have a tendency to invade adjacent structures early in their course. Encasement of the carotid arteries, airway invasion, and vertebral column invasion are common, as are nodal and distant metastases.

Other thyroid malignancies include medullary carcinoma, lymphoma, and metastatic disease. The imaging features of these tumors are generally nonspecific, and tissue sampling and correlation with clinical history and laboratory markers of disease are necessary to make an accurate diagnosis.