The vertebral bodies in the cervical spine are ladder-like in cross section; they are broader in the transverse diameter than in the anteroposterior (AP) dimension, and their end plates are parallel (Fig. 3-1). The cervical vertebral bodies are smaller than those of the other movable vertebrae and increase in size from C3 downward. The vertebrae are connected by the anterior and posterior longitudinal ligaments. Each ligament’s fibers diverge at each disc level and blend with the anulus fibrosus and the adjacent margins of the vertebral bodies. At the mid-vertebral level, the posterior longitudinal ligament is narrower and lies behind the body, posterior to the retrovertebral venous plexus.

Figure 3–1 T1-weighted coronal MR image shows the outline of the cervical spine. The cervical vertebral bodies are stepladder-like in this view. The bodies are broader in the transverse diameter than superoinferior dimension.

Joints of von Luschka

The upper and lateral edges of the superior surface project upward and have sagittal ridges that form the uncinate processes. Together with corresponding notches in lower end plates of the vertebra above, they form the uncovertebral joints of von Luschka (Fig. 3-2).

Figure 3–2 T2-weighted coronal MR image presents the uncovertebral joints of von Luschka (large arrows). The uncinate process from the upper lateral edge of the superior surface of the lower vertebral body faces the lower lateral notch in the lower end plate of upper vertebral body. Small arrows indicate the vertebral arteries.

Transverse Foramen

The transverse foramen, a characteristic feature of the cervical spine, houses the vertebral artery, veins, and sympathetic nerves in the deep cranial groove of the transverse process. The spinal nerves and ganglia cross the dorsal border of the artery along with segmental vessels. The transverse foramen of the seventh cervical vertebra contains only vertebral veins, not the vertebral artery (Figs. 3-3 and 3-4).

Figure 3–3 Axial CT scan of the seventh cervical vertebra. The transverse foramen of the seventh cervical vertebra contains only vertebral veins (thin arrow), not the vertebral artery (thick arrows). However, the other cervical vertebrae contain the vertebral artery within their transverse foramina. See also Fig. 3-4.

Figure 3–4 T1-weighted axial MR image corresponding to the CT scan in Fig. 3-3. The vertebral arteries are revealed as signal voids (arrows) anterior to the transverse foramina.

Spinal Canals

The spinal canals are relatively large in order to house the cervical enlargement of the spinal cord. The spinal canal is triangular with the apex of the triangle posterior. The canal decreases in size from vertebra C1 through vertebra C3 and has a fairly uniform dimension from C3 through C7. C7 is a transitional vertebra, whose spinous process is longer and thicker and has a more inferior tilt than the more rostral cervical spinous processes of C3 to C6. On a T1-weighted MR image, the exact size of the subarachnoid space is difficult to assess because of its low signal intensity, and it may be confused with the posterior longitudinal ligament and the cortical bone (Fig. 3-6).

Figure 3–6 The subarachnoid space, the posterior longitudinal ligament, and the cortical bone reveal low signal intensity on this T1-weighted MR image. They cannot be defined individually.

Epidural Space

The epidural space that surrounds the dural sac contains neurovascular and connective tissue elements that are more clearly seen on MRI and CT after intravenous injection of a contrast agent. There is only a small amount of epidural fat tissue, and sinuses are formed in this fat tissue by the wide venous plexuses that surround roots and nerves as they leave the intervertebral foramina in the lateral parts of the epidural space (Fig. 3-7). The scarcity of revised epidural fat in the cervical canal in comparison with that in the lumbar canal makes it more difficult to differentiate between the soft tissue structures in the cervical spinal canal on a noncontrast CT scan. On MRI, the high signal intensity in the anterior lateral aspect of the cervical canal represents the epidural venous plexus. The epidural venous plexuses produce high signal intensity in the anterior epidural space, which should not be confused with epidural fat; epidural fat is virtually absent at the cervical level.

Figure 3–7 There is little epidural fat tissue in the cervical spine. Wide venous plexuses surround roots and nerves in the lateral aspect of the epidural space and the vertebral artery within the transverse foramen on this contrast-enhanced axial CT scan.

Cervical Discs

The cervical intervertebral discs are smaller than the discs of other regions of the spine. The uncinate processes on the upper end plate limit lateral extension of the discs. These discs are wedge-shaped, the greater width being anterior, corresponding to the cervical lordosis [2]. The intervertebral discs do not extend anteriorly or posteriorly beyond the level of the vertebral body in younger people. The nucleus pulposus cannot be differentiated from the anulus fibrosus, but the periphery of the disc is less intense than its central portion. (Figs. 3-6 and 3-8).

Figure 3–8 On T2-weighted sagittal MR images, high signal intensity can be seen in the nucleus pulposus and the anulus pulposus, which thus cannot be differentiated. The periphery of the disc shows a slightly lower signal intensity than the center.

Nerves of the Cervical Cord

Spinal nerves arise from the cervical cord. Each nerve consists of a dorsal sensory root and a ventral motor root. The nerve roots join just lateral to the dural sheath to form the spinal nerves. The dorsal root ganglion is located in the neural foramen just proximal to the point of union of the dorsal and ventral roots. The roots of each spinal nerve from C1 through C7 leave the spinal canal through the intervertebral foramina above the corresponding vertebra. The eighth cervical nerve passes through the foramen between C7 and T1. The spinal ganglion, located outside and below the neural foramen, is clearly seen posterior to the vertebral artery on MRI as a structure of intermediate signal intensity. On contrast-enhanced MR images, the spinal ganglion appears as a mildly enhancing ovoid structure posterior to the vertebral artery (Fig. 3-9).

Figure 3–9 On a contrast-enhanced T1-weighted axial MR image, the spinal ganglion shows intermediate signal intensity posterior to the vertebral artery (arrows).

Vertebral Arteries

The vertebral arteries usually enter the foramina at the C6 level but may enter at C5 or C7, and they exit the foramina in the area of the transverse process of the atlas; they wind around the lateral masses, passing in a group just posterior to the superior articular facet, from the cranial surface to the posterior arch [3]. The two vertebral arteries penetrate the dura and are well demonstrated on each side of the medulla on contrast-enhanced CT. Within the transverse foramen (Fig. 3-10), the vertebral artery is of low signal intensity (Fig. 3-11), and the vertebral vein of high signal intensity, on MRI. The vertebral vein surrounds the vertebral artery.

Figure 3–10 The vertebral artery (arrow) exits the transverse foramen of the atlas, curves posterolaterally, penetrates the dura, and enters the spinal canal, as seen on this contrast-enhanced axial CT scan.

Figure 3–11 The common carotid arteries, the internal jugular veins, and the vertebral arteries have low signal intensity on this T2-weighted axial MR image. Sometimes, slow-flowing veins have intermediate to high signal intensity on MRI.

Venous Plexus

The cervical epidural venous plexus is an extensive sinusoidal network in the cervical epidural space; it consists of medial and lateral longitudinal channels in the anterolateral portion of the epidural space. The medial and lateral longitudinal channels are connected behind each vertebral body by retrocorporeal veins that communicate with the basivertebral venous system at the midportion of each vertebral body, as follows (Fig. 3-12):

▪ The anterior internal veins, which lie behind the vertebral bodies, receive veins from the ventral dura and vertebral bodies.

▪ The posterior internal veins, which lie ventral to the vertebral arches and ligamenta flava receive veins from these structures.

▪ The external venous plexus lies outside the vertebral channel, along the surfaces of the vertebral bodies, and communicates with the internal plexus through veins in the neural foramina.

▪ The longitudinal channels communicate with the foraminal venous plexus, which extends anteriorly to surround the vertebral artery on each side.

Figure 3–12 Contrast-enhanced MR venography shows an extensive sinusoidal network in the cervical epidural space. Each level of the cervical spine reveals the basivertebral vein (BV) communicating with the anterior longitudinal epidural veins (ALV) via the retrocorporeal veins (RV). The venous plexus (VP) surrounding the vertebral artery connects the longitudinal veins via the communicating veins (CV).

This system is an intricate, lattice-like network composed of slowly flowing blood [3]. The veins can be seen on both sagittal and axial MR images as areas of increased signal intensity. Parasagittal views demonstrate them best in the anterolateral recess of the cervical spinal canal. Increased intensity denotes slow to stagnant venous flow. Axial images show these segmented longitudinal bandlike channels as areas of high signal intensity in the anterolateral recess of the spinal canal. Though often seen on noncontrast studies, the epidural venous plexus can be unclear, depending on the direction and velocity of blood flow. It is more consistently and accurately depicted after the administration of gadolinium-DTPA, which produces a uniformly high signal intensity of the epidural venous structures outside the extradural space, along the anterolateral aspects of the spinal canal and neural foramina.

The thoracic spine

The 12 thoracic vertebrae are intermediate in size between the smaller cervical and larger lumbar vertebrae. The vertebral bodies and their discs have an inverted heart shape in cross section. The end plates of the vertebral bodies are flat, and the nuclei pulposi are more centrally located than in the lumbar discs. The thickness and the horizontal dimensions of the thoracic discs increase caudally. Although the thoracic discs are of larger volume than the cervical discs, they are thinner vertically than cervical and lumbar discs (Fig. 3-13). The thoracic vertebrae are characterized by costal facets on both sides of the bodies and on all the transverse processes except those of the 11th and 12th thoracic vertebrae, which articulate with facets on the heads and tubercles, respectively, of the corresponding ribs (Fig. 3-14).

Figure 3–13 T2-weighted sagittal MR image. Thoracic vertebral bodies and discs increase in transverse and vertical dimensions caudally. The hyperintense posterior epidural fat is defined by anteriorly located, thin, hypointense dura (black arrows).

Figure 3–14 Axial CT scan at the mid-thoracic level. The costal facet (thin black arrow) on the posterolateral side of the body faces the corresponding head of the rib. Another characteristic of the thoracic vertebrae, the transverse process (thick black arrow), articulates with the tubercle of the rib. The pedicle projects posteriorly, and the dural sac is round. The laminae are short and relatively thick.

Pedicles

The stout pedicles of a thoracic vertebra arise from the upper half on the dorsum of the body and pass posterolaterally and slightly inferiorly to the articular pillar and posterior neural arch. On axial MR images or CT scans, the facet joints demonstrate a coronal orientation (Fig. 3-15).

Figure 3–15 The facet joints demonstrate a coronal orientation.

Laminae

The laminae are short and relatively thick. They pass from the articular pillars in a medial and posterior direction. They partly overlap each other from T1 downward (see Fig. 3-14).

Spinous Process

The spinous process in the thoracic region is longer and more slender than in the lumbar region and appears triangular in section. The spinous processes of the upper and lower four vertebrae are more bladelike and are directed backward horizontally. The middle four thoracic spines are longer and are inclined downward and backward, so that their spines completely overlap the next lower segments.

Transverse Process

The transverse processes run laterally, superiorly, and posteriorly from the articular pillars. They are closely related to the heads, necks, and tubercles of the corresponding ribs.

Articular Processes

The superior articular processes project upward from the junctions of the pedicles and the lamina on each side, and their facets slant backward and slightly outward. At the inferior edge of the lamina, the inferior articular processes project downward and forward, and their facets face forward, slightly downward and inward.

Intervertebral Foramen

The intervertebral foramen, smaller and more rounded than in the cervical region, is directed laterally at the inferior half of the vertebral body. Its margins are formed by the pedicles superiorly and inferiorly, the vertebral body anteriorly, the neck of the rib anterolaterally, and the facet joints posteriorly. The nerve roots, surrounded by the abundant foraminal fat, are of intermediate signal intensity (Fig. 3-16).

Figure 3–16 The intervertebral foramen is round to ovoid at the inferior half of the vertebral body. Its margins are formed by the pedicles superiorly and inferiorly, the vertebral body anteriorly, the neck of the rib anterolaterally, and the facet joints posteriorly. The nerve roots (arrows), surrounded by the abundant hyperintense foraminal fat, are of intermediate signal intensity on this T1-weighted sagittal MR image.

Spinal Canal

The spinal canal is ovoid in cross section, with a relatively large anteroposterior diameter. Epidural fat is abundant posteriorly between the neural arch and the dura, and laterally in the intervertebral foramen. It is, however, less abundant in the anterior half of the epidural space than in the lumbosacral region. The posterior epidural fat demonstrates high signal intensity on T1-weighted and T2-weighted MR images (Figs. 3-17 to 3-19). The posterior longitudinal ligament is difficult to differentiate from the dural sac. Venous sinuses widely occupy the lateral recesses and intervertebral foramina.

Figure 3–17 Epidural fat (black arrows) located posteriorly between the neural arch and the dura, and laterally in the intervertebral foramen, demonstrates high signal intensity like the subcutaneous fat tissue on this T2-weighted axial MR image. The back muscles have intermediate signal intensity.

Figure 3–18 Epidural fat (arrows) has high signal intensity on a T1-weighted axial MR image.

Figure 3–19 There is little anterior epidural fat. Posterior epidural fat is different from the anteriorly located hypointense dural sac. Ill-defined multiple longitudinal vertical lines in the middle of this MR image represent a motion artifact of the heart.

Conus Medullaris

The conus medullaris, the cone-shaped lower bulging of the spinal cord, projects at the T12-L1 level, and its tip is located at L2-L3. The cauda equina, named for its resemblance to the tail of a horse, is located in the posterior aspect of the canal on axial MR images or CT scans.

The lumbar spine

The lumbar vertebrae, the lowest five of the presacral column, are distinguished by their lack of transverse foramina or costal facets. The lumbar vertebral bodies are large, round or elliptical, and wider from side to side than from front to back. Their upper and lower body margins are flat or slightly concave. They have convex anterior and lateral margins with a flat or concave posterior margin.

Pedicles and Spinous Processes

The pedicles are short and strong, and they project posterolaterally from the upper aspects of the vertebral bodies. They form the upper and lower margins of the neural foramen.

The broad and thick laminae project from the pedicles and meet in the midline to form the spinous process. The large, rectangular spinous processes extend dorsally.

Transverse and Accessory Processes

The flat transverse processes run laterally and slightly posteriorly from the junction of the pedicle (Fig. 3-20). The thick, rounded fifth transverse process sometimes articulates with the iliac bones but also can be fused with the ilium.

Figure 3–20 Axial bone window CT scan of the lumbar spine at the level of the pedicle. Short and thick pedicles project posterolaterally from the upper aspect of the vertebral body. The laminae project from the pedicles and meet in the midline to form the spinous processes. The spinous processes extend dorsally. The flat transverse processes run laterally and slightly posteriorly from the junction of the pedicle. Accessory processes (arrows) project from the posterior and inferior surfaces of the bases of the transverse processes.

The accessory processes project from the posterior and inferior surfaces of the bases of the transverse processes.

Articular and Mammillary Processes

The superior articular processes project vertically upward from the articular pillars between the pedicles and the laminae. The concave facet of each superior articular process faces dorsomedially to the inferior articular facets of the vertebra above it (Fig. 3-21). At the inferior aspect of the intervertebral foramen, the superior articular facet becomes contiguous with the pedicle below to form the posterior border of the lateral recess. At this point, the traversing nerve root lies medial to the pedicle, anterior to the superior articular facet, and posterior to the vertebral body and disc [4,5]. The inferior articular processes run downward and slightly laterally from the laminae. Their articular surfaces face ventrolaterally to the superior articular facets of the vertebrae below them. The articular plane is curvilinear.

Figure 3–21 Axial bone window CT scan of the lumbar spine at the level of the disc. The concave facet of the superior articular processes (S) faces dorsomedially to the inferior articular facets (I) of the vertebra above them. The mammillary processes (arrow) projecting backward from the superior articular process are short and round for the attachment of muscles.

The mammillary processes project backward from the superior articular process and are short and round for the attachment of muscles (see Fig. 3-21).

Intervertebral Foramina

The intervertebral foramina are defined anteriorly by the posterior vertebral bodies and disc, superiorly and inferiorly by the pedicles, and posteriorly by the articular processes. The intervertebral foramina are the largest in the lumbar area. The spinal ganglia, the spinal branch of the segmental artery, and the sinuvertebral nerve are located in the upper portion of each intervertebral foramen, and the intervertebral veins in the lower portion (Figs. 3-22 and 3-23).

Figure 3–22 T1-weighted sagittal MR image. Note the well-defined intervertebral foramina, which are are largest in the lumbar area. The neural elements (thick black arrow) are located in the upper portion of each intervertebral foramen, and the intervertebral veins (thin black arrow) in the lower portion.

Figure 3–23 T2-weighted sagittal MR image of the intervertebral foramina. The neural elements and vascular structures are surrounded by hyperintense epidural fat.

Spinal Canal

The spinal canal, which is round or oval at L1, is increasingly triangular toward the lower lumbar vertebrae. It takes on a V shape at the S1 level (Fig. 3-24, 3-25).

Figure 3–24 The spinal canal, which is round or oval at L1 (A ), is increasingly triangular toward the lower lumbar vertebrae (B ). It then takes on a V shape at the S1 level (C ).

Figure 3–25 Three of the various configurations of the spinal canal.

Meninges

The three layers of meninges (dura mater, arachnoid, and pia mater) that surround the brain also continuously envelop the spinal cord. The dura mater, a dense fibrous tissue extending distally to the S2 segment, is separated from the vertebral canal by an epidural fat layer and a venous plexus. The arachnoid membrane is loosely attached to the dura but is separated from it by a small subdural space. These structures are usually indiscernible from underlying cerebrospinal fluid on CT or MRI. The pia mater is a thin connective tissue closely attached to the spinal cord and its nerve roots.

Epidural Space

The epidural space between the dura and the bones of the spinal canal contains epidural fat, spinal nerves, blood vessels, and ligaments. The epidural fat space is prominent ventral to the dura at the mid-body level of the lumbar vertebrae, especially L5-S1 (Fig. 3-26). The abundant epidural fat makes it easy to differentiate other structures, such as the nerve roots, the venous plexus, and the margin of the discs, on CT and MRI.

Figure 3–26 Axial CT scan at the level of the L5-S1 disc. The dura, the nerve root sheath, the ligamentum flavum, and the disc are well-defined owing to abundant epidural fat. The disc and the ligamentum flavum show mild hyperattenuation in comparison with the dural sac.

Ligaments of the Lumbar Spine

The posterior longitudinal ligament covers the posterior vertebral bodies with some space for the vascular structures. At the level of the intervertebral discs, it attaches tightly to the posterior surface of the anuli of the discs. The ligamentum flavum is 5 mm thick and extends from the anteroinferior border of the lamina above to the upper posterior border of the lamina below. The ligamentum flavum is hyperintense to the bony cortex of the lamina on T1-weighted MR images (Fig. 3-27). Laterally its fibers blend with the thick medial and superior portions of the facet capsule. The anterolateral extension of the ligamentum flavum fuses laterally with the medial portion of the facet joint capsule to reinforce the capsule [6].

Figure 3–27 The ligamentum flavum is slightly hyperintense to the bony cortex of the lamina on this T1-weighted MR image. Epidural fat is strongly hyperintense to the ligamentum flavum. A small focal hyperintensity (short thin arrow) in the posterior midline of the dural sac is due to fatty change of the filum terminale. The dorsal ganglion (thick arrows) is isointense to the muscles. The epidural venous plexus appears as punctuate foci of low signal intensity within the hyperintense epidural fat (long thin arrows).

Nerves of the Lumbar Spine

The lumbar spinal nerve roots lie in the lateral recess and extend to the medial border of the superior articular facet at the lower portion of the vertebral foramen of the level above. The nerves then pass laterally below the pedicle and enlarge to form the dorsal ganglion (see Fig. 3-27). From the ganglion, the peripheral nerves exit laterally out the vertebral foramen.

The nerve roots, which are smaller ventrally and larger dorsally, exit through an intervertebral foramen. The dorsal root becomes the spinal ganglion in the lateral portion of the intervertebral foramen (see Fig. 3-27). Lying together, they pierce the dura and unite to form a spinal nerve. The spinal nerves are interconnected with adjacent sympathetic trunk ganglia by rami communicantes, providing an explanation for the mutual overlapping of segmental sensory nerve distribution. Small recurrent meningeal branches originate from the spinal nerves shortly after emerging from the intervertebral foramina, and they innervate the meninges and their vessels. Then the spinal nerves divide into the ventral and dorsal rami. The ventral rami supply the anterior and lateral parts of the trunk. The dorsal rami turn backwards to supply the cutaneous and muscular regions and the facet joints (Fig. 3-28).

Figure 3–28 The spinal nerves divide into the ventral and dorsal rami. The ventral rami supply the anterior and lateral parts of the trunk. The dorsal rami turn backwards to supply the cutaneous and muscular regions and the facet joints.

Lumbar Venous Plexus

The epidural venous plexus appears as punctuate foci of low signal intensity within the hyperintense epidural fat (see Fig. 3-27).

The basivertebral veins, from the cancellous vertebral bodies, drain into the anterior internal vertebral plexus in the midportion of the posterior vertebral body. They also drain into the anterior external plexus through many openings in the anterior and lateral surfaces of the vertebral body. Two external vertebral plexuses, anterior and posterior, existed as follow; The anterior external plexus lies in the anterior surface of the vertebral bodies. The posterior external plexus lies over the vertebral laminae and extends around the vertebral processes.

Lumbar Disc

The intervertebral disc in the lumbar region has three parts: the cartilaginous end plate, the anulus fibrosus, and the nucleus pulposus [7]. The intervertebral discs are thickest in the lumbar region. Lumbar lordosis is due to the increase in differential between the anterior and posterior thicknesses of the discs, a situation that makes the lumbosacral disc the most wedge shaped ^[8]. On axial sections, the upper four lumbar discs have a slightly concave or flat posterior border, conforming to the adjacent V-shaped bodies. The fifth lumbar disc, however, has a flatter, slightly convex posterior border (Fig. 3-29).