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Magnetic resonance imaging (MRI) is a very useful tool for assessing the cervical spine because it provides high-resolution multiplanar images of both osseous and soft tissue structures. The specifics of MRI image acquisition and physics are discussed in detail elsewhere. The emphasis of this chapter is the utility of MRI in the diagnosis of different pathologic processes of the cervical spine.
Pulse Sequences
Although the specifics of MRI procurement are discussed in detail elsewhere, the clinician should be able to identify the basic pulse sequences and be aware of the roles they play in imaging the cervical spine. Imaging protocols of the cervical spine vary by institution, but standard MRI sequences of the cervical spine include the following: sagittal T1-weighted spin-echo (SE), sagittal T2-weighted fast SE, axial gradient-echo, and axial T2-weighted fast SE.
T1-weighted images are best used to evaluate anatomy, fracture lines, and other osseous details. T2-weighted images are excellent for evaluating spinal cord parenchyma for lesions and edema. T2-weighted images are sensitive to pathologic changes in tissue, including any cellular process that increases the local water content. Gadolinium contrast–enhanced T1-weighted images are useful for assessing neoplasms, infections, and the postoperative spine. Fat-suppressed T2-weighted fast SE and short tau inversion recovery images accentuate fluid and edema and make abnormalities more conspicuous by eliminating the signal of fat. Gradient-echo images help detect degenerative changes, including osteophytes and neural foraminal narrowing. The susceptibility of gradient-echo sequences to magnetic artifact make it ideal for detecting areas of hemorrhage, such as those from trauma, or vascular malformations.
Steps in Cervical Spine Image Interpretation ∗
∗ Adapted from Khanna AJ, Carbone JJ, Kebaish KM, et al: Magnetic resonance imaging of the cervical spine: current techniques and spectrum of disease. J Bone Joint Surg Am ; 84:70–80, 2002.
The complex anatomy of the cervical spine can be difficult to evaluate. A systematic approach to imaging can greatly enhance the interpretation of the images. The following algorithm, proposed by Khanna and associates, is one approach to the interpretation of MRI of the cervical spine:
- 1.
Determine the pulse sequence for all images.
- 2.
Locate the T2-weighted midsagittal image. Evaluate all normal structures.
- 3.
Serially evaluate all parasagittal images in each direction toward the facet joints and neural foramina. Use the coronal localizer to confirm right-left orientation.
- 4.
Repeat steps 2 and 3 for other pulse sequences (usually T1 and occasionally gradient-echo and postgadolinium T1).
- 5.
Locate the odontoid process on the T2-weighted axial images. Serially evaluate all images from the odontoid toward the first thoracic vertebra (determined by the presence of ribs). Use the intervertebral disks and sagittal localizer to confirm levels. Repeat this process for other pulse sequences.
- 6.
Correlate the MRI findings with the clinical history to arrive at the most likely differential diagnosis.
Normal Anatomy †
† Adapted from Khanna AJ, Carbone JJ, Kebaish KM, et al: Magnetic resonance imaging of the cervical spine: current techniques and spectrum of disease. J Bone Joint Surg Am ; 84:70–80, 2002.
Before one can recognize the subtleties of pathologic processes, it is important to gain an appreciation of normal anatomy. When evaluating a cervical MRI scan, close attention should be paid to the following structures ‡
‡ Adapted from Takhtani D, Melhem ER: MR imaging in cervical spine trauma. Magn Reson Imaging Clin N Am ; 8:615–634, 2000.
:- •
Spinal column and vertebral bodies: alignment, vertebral body fracture, posterior element fracture, edema, degenerative change
- •
Ligaments: anterior longitudinal ligament, posterior longitudinal ligament, interspinous ligaments, edema or rupture
- •
Spinal cord: edema, hemorrhage, compression, syrinx
- •
Epidural space: hematoma, disk herniation, osseous fragment
- •
Vascular: vertebral artery
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.
Cervical Spine Disorders
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 Pathology | Magnetic Resonance Imaging Findings |
|---|---|
| Bulge | Symmetric extension of annulus beyond the confines of adjacent end plates |
| Protrusion | Focal area of disk material that extends beyond vertebral margin but remains contained within the outer annular fibers |
| Extrusion | Herniation of nucleus pulposus beyond the confines of the annulus with disk attached to the remainder of nucleus pulposus by a narrow pedicle |
| Sequestration | Portion of disk fragment entirely separated from the parent disk |
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.
| 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 |
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