Magnetic Resonance Imaging of the Cervical Spine

Sagittal Images

Following the approach outlined previously, and starting with midsagittal image of the T2-weighted sequence, the full profile of the odontoid, most vertebral bodies, and the spinal cord can be appreciated in patients without scoliosis. The facet joints and neural foramina are assessed next on parasagittal images. The dorsal and ventral nerve roots can be visualized within the neural foramina. The nerve roots show intermediate signal intensity and are surrounded by high-signal-intensity fat on T1-weighted images ( Fig. 10-1 ). While panning lateral to the midsagittal plane, the clinician can evaluate end plate and osteophyte anatomy and the margins of the anterior and posterior longitudinal ligaments.

Healthy intervertebral disks show intermediate signal intensity on T1-weighted images and high signal intensity on T2-weighted, gradient-echo, and T2-weighted images. For vertebral bodies, the normal fatty marrow shows bright signal intensity on T1-weighted images. A lordotic curvature of the cervical spine is expected, with tapering of the spinal canal diameter initially from the first to the third cervical vertebrae and a constant diameter thereafter ( Fig. 10-2 ). The entry site of basivertebral veins can often be seen at the midposterior portions of the vertebral bodies. The short cervical pedicles are seen on the parasagittal images ( Fig. 10-3 ).

Cerebrospinal fluid is seen as low signal intensity on T1-weighted images and as high signal intensity on T2-weighted images. Spinal cord sagittal T2-weighted images provide a myelographic effect that allows evaluation of spinal cord morphology and evaluation for extrinsic compression. The spinal cord usually has a homogeneous signal without intrinsic abnormality. Ligaments show low signal intensity on all sequences. Ligaments that are important to identify in the review of sagittal images include the transverse ligament, ligamentum flavum, and anterior and posterior longitudinal ligaments. The transverse ligament lies posterior to the odontoid process. The ligamentum flavum starts superiorly as a hypointense band just posterior to the dura and descends to the posterior aspect of the spinal canal. The anterior and posterior longitudinal ligaments typically adhere to the vertebral column.

Axial Images

Accurate identification of the vertebral level is always challenging on axial MRI scans. Most modern MRI studies provide a sagittal localizer, but in its absence, the level can be determined by identifying the odontoid process and numbering each vertebral body from that level. The difference in intervertebral disk and vertebral body signal facilitates distinction between vertebral levels. At each vertebral level, the spinal canal morphology, the traversing spinal cord, and associated roots should be scrutinized.

Coronal Images

Although almost all spinal structures can be examined with sagittal and axial images alone, coronal plane images should be reviewed to confirm normal anatomy. In addition, coronal plane images add an indispensable perspective when evaluating pathologic features in the presence of coronal plane deformities such as scoliosis, particularly with regard to the morphology of the neural foramen, lateral recesses, and facet joints.

Degenerative Disk Disease

Degenerative abnormality can affect multiple areas of the cervical spine, including intervertebral disks, facet joints, uncovertebral joints of Luschka, ligaments, and paravertebral musculature. MRI is considered the preferred initial advanced imaging modality for the evaluation of symptomatic cervical spine degeneration, with a reported sensitivity and specificity of 91% each for the detection of cervical degenerative changes. Despite this high sensitivity and specificity, however, MRI abnormalities do not always correlate with symptomatic degenerative lesions. Boden and associates reported that almost 60% of asymptomatic patients who were more than 40 years old had cervical spine degenerative disk disease on MRI. Therefore, correlating a patient’s history and physical examination with imaging findings is of paramount importance.

The structural composition of the intervertebral disk changes with age: the water content of the nucleus pulposus and annulus fibrosis decreases from approximately 90% in the first year of life to 70% to 75% in the eighth decade. Disk desiccation results in bulging of the annulus fibrosus and concomitant loss of disk height; the result is increased stress transfer to the facet and uncovertebral joints that propagates osteocartilaginous hypertrophy and osteophyte formation. On MRI, a normal intervertebral disk has intermediate signal intensity on T1-weighted images and high signal intensity on T2-weighted images, whereas disk desiccation is seen as low signal intensity on T1-weighted and T2-weighted images ( Fig. 10-4 ). Degeneration and desiccation of the annulus fibrosus can result in annular tears. Tears manifest as areas of high signal intensity within the annulus on T2-weighted sequences ( Fig. 10-5 ). A weakened annulus fibrosus may lead to a spectrum of intervertebral disk abnormality based on the extent of annulus bulging and disk herniation ( Table 10-1 ). Findings of degenerative disk disease on MRI should always be correlated with cervical radiographs.

Disk herniation resulting from degenerative disease can impinge on structures in the spinal canal. The size of the disk abnormality is less important than the degree of the mass effect on neighboring neural structures. The direction and location of herniation (i.e., central, paracentral [left-right], foraminal, or far lateral) should be noted and carefully correlated with the patient’s history and examination.

In addition to being evaluated for the level, direction, and configuration of disk displacement, the MRI should also be scrutinized for the presence or absence of areas of calcium deposition, anterior or posterior osteophyte formation, and vertebral end plate changes. These findings should be correlated with lateral and oblique cervical spine radiographs.

Cervical stenosis secondary to disk displacement must be distinguished from ossification of the posterior longitudinal ligament because treatment algorithms for each condition are distinct. Stenosis secondary to disk abnormality is seen only posterior to the vertebral disk (in the absence of extrusion with migration) ( Fig. 10-6 ). In contrast, stenosis in patients with ossification of the posterior longitudinal ligament is shown on MRI along the course of the posterior longitudinal ligament, not just posterior to the disk ( Fig. 10-7 ). In patients with suspected ossification of the posterior longitudinal ligament, computed tomography (CT) imaging provides optimal visualization of calcification in the ligament and helps confirm this diagnosis.

Spinal Stenosis

General Description

Spinal stenosis can have congenital or acquired causes ( Table 10-2 ). On MRI, central canal stenosis is characterized by focal or concentric compression of the thecal sac that is best seen on sagittal and axial T2-weighted images. The cerebrospinal fluid around the spinal cord produces a bright signal anterior and posterior to the cord on midsagittal images and circumferentially around the spinal cord on axial images. Parasagittal images allow for visualization of lateral recess and foraminal stenosis. The degree of central spinal canal stenosis can range from mild encroachment on the ventral subarachnoid space to severe compression and flattening of the spinal cord with myelomalacia. MRI findings may correspond to the severity and duration of the compression. Acute spinal cord compression can produce spinal cord edema with high-signal areas on T2-weighted images. Progressive compression may trigger spinal cord atrophy ( Fig. 10-8 ), cystic degeneration, and syrinx formation.

Table 10-2

Acquired and Congenital Factors Associated with Spinal Stenosis

From Zebala LP, Buchowski JM, Daftary AR, et al: The cervical spine. In Khanna AJ, editor: MRI for orthopaedic surgeons, New York, 2010, Thieme, pp 229–268.

Type	Factor
Acquired	Intervertebral disk disease
	Uncovertebral joint hypertrophy
	Facet joint hypertrophy
	Ligamentous (ligamentum flavum hypertrophy or ossification, ossification of the posterior longitudinal ligament, diffuse idiopathic skeletal hyperostosis)
	Spondylosis
	Metabolic conditions
	Postinflammatory status
	Spondylolisthesis
	Postoperative status
	Neoplastic disorders
Congenital	Idiopathic condition with short pedicles
	Skeletal growth disorders
	Down syndrome
	Achondroplasia
	Mucopolysaccharidosis
	Scoliosis

Several objective measures of cervical spinal stenosis have been proposed. Relative stenosis and absolute stenosis of the spinal canal are defined as an anteroposterior canal diameter of less than 13 mm and 10 mm, respectively. The Torg or Pavlov ratio is calculated by dividing the anteroposterior spinal canal diameter by the anteroposterior vertebral body diameter; a ratio of less than 0.8 is defined as stenotic.