CT and MRI provide complementary information about degenerative diseases of the spine. MRI is often the modality of choice in assessing degenerative changes within the spine due to its superior soft-tissue contrast. CT has superior spatial resolution and provides better conspicuity of osseous and calcified structures. The advent of MDCT technology allows for superb reconstruction in the sagittal and the coronal planes that allows for better depiction of pathologic processes and hardware evaluation in the post–operative spine (57). MRI permits noninvasive visualization of the spinal cord and subarachnoid space within the spinal canal and the nerve roots within the neural foramina. Discrimination of these structures by CT requires injection of intrathecal contrast agents. MRI has a superior ability to evaluate intramedullary abnormalities. It also offers direct multiplanar imaging capabilities.
Axial CT images of the normal cervical and lumbar spine (Figs. 6-44 and 6-45) provide good visualization of all osseous elements, including the facet joints. In the cervical spine, the uncovertebral joints (i.e., Luschka) are well depicted with coronal reformatted and sagittal oblique images. Sagittal oblique images through the lumbar spine provide excellent anatomical reconstruction of the pars interarticularis for the assessment of spondylolysis. Soft-tissue windows typically permit visualization of the moderate radiodensity of the soft- tissue structures, such as the intervertebral disc, ligamentum flavum, and thecal sac. Sagittal images provide assessment of anatomical alignment, intersegmental instability and allows for adequate evaluation of foraminal stenosis. The epidural fat contains the internal vertebral venous plexus, which can be enhanced by a circulating bolus of contrast material to improve visualization of soft-tissue encroachments into the spinal canal, such as herniated discs. Introduction of contrast material into the subarachnoid space (i.e., CT myelography) delimits the contained spinal cord and the nerve roots (Fig. 6-46).
FIGURE 6-44. MDCT of the normal cervical spine. A: Bone window CT of the cervical spine in the axial plane at the level of C5-6 displays normal facet joints (short arrow) and Luschka joints (long arrow). B: Coronal multiplanar reformatted images (MPR) through the level of the uncovertebral joints (arrow). C: Midplane sagittal reconstructed images of the cervical spine shows mild reverse of the normal lordosis that could be secondary to spasm or associated to positioning. Note adequate alignment and no intersegmental subluxations. D: Sagittal oblique MPR demonstrates the nerve root foramina, uncovertebral joints, and facet joints.
FIGURE 6-45. Normal lumbar spine CT. A: Axial soft-tissue window CT of L5 demonstrating thecal sac (T), L5 nerve root (NR) within the lateral recess, epidural fat (E), and ligamentum flavum (LF). B: Bone windows axial through the same level demonstrate the sclerotic margins of the facet joint and the right sacroiliac joint. C: Midplane sagittal reconstruction (MPR image). Normal homogeneous trabecular pattern. Note intervertebral space distance and anatomical alignment of the anterior and posterior surface to the vertebral bodies. D: The density of the nucleus pulposus (NP) and annulus fibrosus (AF) can be appreciated. Note decreased attenuation to the CSF in the thecal sac. E: Oblique reconstruction through the posterior elements demonstrating the normal facet joints and pars interarticularis.
FIGURE 6-46. Metrizamide CT myelogram at L1 level delimiting the spinal cord (SC), nerve roots (NR) arising from the cord, and the contrast-enhanced CSF.
The introduction of MDCT technology allows for the acquisitions of multiple thin cut images in the axial plane that can be reconstructed in the sagittal and the coronal planes. The high spatial resolution of the acquired data allows for near-perfect isometric reconstruction in different planes. In addition, computer-generated volume rendering images provide superb 3D images of the spine (Fig. 6-47A–C).
Sagittal T1-weighted MR images of the cervical, thoracic, or lumbar spine provide excellent noninvasive survey to evaluate patients with suspected regional spinal pathology. Midsagittal T1-weighted images display the high–signal-intensity marrow of the vertebrae bordered by low–signal-intensity cortical bone. Structures displaying very low signal intensity include the peripheral part of the annulus fibrosus of the intervertebral disc, all ligaments, the dura, and the cerebrospinal fluid (CSF), and these are usually indistinguishable from each other (Fig. 6-48A–C). The nucleus pulposus, and probably the inner portion of the annulus fibrosus, shows moderate signal intensity. The spinal cord and the nerve roots display moderate signal intensity, which is well contrasted against the low–signal-intensity CSF. Collections of epidural fat, which are largest at lumbar levels, produce high signal intensity on T1-and T2-weighted images. On T2-weighted MR images, CSF and the normal well-hydrated nucleus pulposus assume high signal intensity.
FIGURE 6-47. Volume rendering images of the normal lumbar spine. A: Coronal (frontal) projection. Arrow points to a hypoplastic right transverse process, a normal anatomical variant. B: Sagittal (lateral) view, note relationship of pars interarticularis (PI) to the facet joint (FJ) and root foramina (RF). C: Midplane sagittal view through the central canal. Facet joint (FJ), pars interarticularis (PI), and pedicle (P).