Although much spinal trauma is well visualized on plain films, CT has a number of advantages over this modality. These include the demonstration of fractures not seen in plain films, an accurate determination of the amount of spinal canal encroachment by fracture fragments (Fig. 6-66A,B), the identification of neural foramen impingement by fractures involving its boundaries, and a more precise evaluation of facet disruption.
MR can display impingement on the dural sac or the spinal cord by bone fragments, as well as any resultant cord contusion (Fig. 6-66C). It can demonstrate acute cord enlargement as a sign of cord edema or hemorrhage and cord atrophy. CT myelography can be used to diagnose post- traumatic cystic myelopathy because the cyst will take up the contrast and be displayed as a well-marginated, homogeneous, high-density region within the cord. When MRI is not available or contraindicated, CT myelograpy can be used to assess the degree of spinal canal stenosis and cord compression.
FIGURE 6-66. MDCT visualization of spinal trauma. A: CT of a burst fracture of L1 shows displacement of a fracture fragment into the spinal canal (arrow ). There is significant comminution to the superior articular surface of the vertebral body. B: Sagittal MPR reconstruction demonstrates the large fragment (arrow ) extending into the spinal canal. There is mild compression of the superior end plate of L2. C: Sagittal T2-weighted MR image demonstrates increased signal intensity to the bone marrow of the L1 and L2 vertebral bodies due to the presence of edema and hemorrhage. There is posterior displacement of the conus and proximal cauda equina in the spinal canal. Increased signal to the conus (arrow) is compatible with a cord contusion.
CT also can augment the interpretation of the signs of vertebral instability seen on plain radiographs (Fig. 6-67A–C) (71). These signs include the following:
- Vertebral displacements involving the whole vertebra or fracture fragments.
- Widening of the interspinous interval, which implies injury to the posterior spinal ligaments secondary to hyperflexion injury.
- Increased dimensions of the vertebral canal in the sagittal or coronal plane often evaluated by an increased interpedicle distance, which implies a complete disruption of the vertebral body in the sagittal plane.
- Widening of the facet joint interval, which implies ligamentous disruption.
- Disruption of the alignment of the posterior aspect of the vertebral bodies, such as occurs in burst fractures or lap-seatbelt fractures (Fig. 6-68).
FIGURE 6-67. A: Axial image at the C5 cervical segment. There is a burst comminuted fracture to the vertebral body. A fracture through the posterior arch is present as well. B: Sagittal MPR reconstruction demonstrates anterior collapse and posterior subluxation in relationship to the adjacent vertebral bodies. C: Sagittal T2-weighted MR shows increased signal to the vertebral body compatible with edema, prevertebral soft-tissue swelling (arrow ) and edema (arrow ) within the interspinous spaces as a secondary sign of ligamentous injury to the posterior supporting ligaments.
FIGURE 6-68. Sagittal T2-weighted image of the thoracic spine. There is a fracture dislocation (Chance fracture) at the C7-T1 inter- space. There is bone marrow edema to the C7, T1, and T2 vertebral bodies and extensive prevertebral soft-tissue swelling. Edema is also appreciated within the posterior supporting structures. There is compression and edema (white arrow ) to the cord extending from C6 up to the T2 segment.
T1-weighted sagittal and axial MR images provide the best evaluation of vertebral alignment and the bony and ligamentous boundaries of the spinal canal. They also allow the best delineation of the low signal intensity of a traumatic syringomyelia against the higher signal intensity of the surrounding spinal cord. T2-weighted sagittal MR images that produce a high– signal-intensity CSF provide the best estimate of the degree of encroachment of a bony fragment on the thecal sac or the spinal cord.
MRI has a number of advantages over other modalities for imaging spinal trauma. First, it permits evaluation of vertebral alignment at the cervicothoracic junction of the spine,
which is relatively inaccessible by other modalities. Second, it provides a means to evaluate adjacent soft-tissue damage. For example, hemorrhage in the prevertebral space that can occur with hyperextension injuries is identified on T2-weighted images as a high–signal-intensity area. MRI also identifies high–signal-intensity hemorrhage in the posterior paravertebral muscles that can occur secondary to hyperflexion injuries. In addition, MRI is the most sensitive modality for the assessment of ligamentous injuries as it detects edema within the supporting ligaments, a finding not assessed by any other imaging modality (Figs. 6-66 and 6-67C). Of importance is the fact that MRI provides a noninvasive means of evaluating the relationship of retropulsed vertebral body fragments or anteriorly displaced neural arch fragments to the spinal cord (Fig. 6-66C). In most centers, MRI has replaced myelography as the procedure of choice for evaluating the effects of vertebral trauma on the spinal cord. Most important, MRI can evaluate the extent and type of spinal cord injury (71,72).
An acutely injured spinal cord tends to enlarge, thereby filling the spinal canal and displacing the epidural fat. This can be visualized by both CT and MRI. However, MRI provides the best means of evaluating the type of spinal cord trauma and its evolution. MRI is valuable in the early stages of spinal cord injury in determining the type of spinal cord injury and the prognosis for recovery. It can identify the level and completeness of cord transection by direct visualization of the transection site. In the nontransected cord, it can discriminate cord hemorrhage from cord contusion with edema. Spinal cord contusion with edema causes high signal intensity on T2-weighted images within the first 24 hours of injury. Acute hemorrhage of less than 24 hours’ duration appears as a low– signal-intensity area on T2-weighted images. Within a few days of the trauma, the subacute hemorrhage site becomes hyper- intense on T2-weighted images as a result of the accumulation of paramagnetic methemoglobin (Fig. 6-69). Kulkarni et al. found that the type of injury visualized by MRI correlated with the patient’s recovery of neurologic function (73). Those patients with cord contusion and edema exhibited significant functional recovery, whereas those with hemorrhage made little functional progress. Therefore, the MRI characteristics of the injury may provide the clinician with important prognostic data.
MRI is also invaluable for identifying late sequelae of spinal cord trauma, including myelomalacia and post-traumatic spinal cord cysts or syringomyelia. Myelomalacia is thought to develop within an injured segment of the spinal cord as a result of ischemia or the release of enzymes from damaged spinal cord tissues, or both (74). The myelomalacic area is made up of the products of neuronal degeneration, scar tissue, and microcysts. It is thought that the myelomalacic areas become larger intramedullary cysts because the scar tissue about the injured cord tethers the cord to the dura so that the episodic changes in CSF pressure that occur during daily activities tend to be concentrated on the injured cord segment as stretching forces. It is hypothesized that these stresses cause coalescence of the myelomalacic microcysts into a progressively enlarging gross cyst. CSF is theorized to enter the cysts along enlarged perivascular Virchow-Robin spaces that connect the subarachnoid space to the cyst.
On T1-weighted images, myelomalacia appears within the segment of the spinal cord near the area of injury as a region of lower signal intensity than the spinal cord but higher signal intensity than the CSF. It has indistinct margins with the surrounding spinal cord. In contrast, intramedullary cysts have signal intensity approximating that of CSF and sharply marginated borders with the surrounding spinal cord or an adjacent area of myelomalacia. The development of an intramedullary cyst in a spinal cord patient whose clinical picture had previously stabilized may cause the patient to develop progressive sensory and motor deficits. Although myelomalacia has no definitive treatment mode, a spinal cord cyst can be surgically decompressed with a shunt to achieve improvement or at least an arrest of the patient’s neurologic deterioration. Therefore, the MRI distinction between cysts and myelomalacia is important. MRI can also be used in postoperative follow-up to ensure that the cyst has been fully decompressed and that the catheter is continuing to function to prevent reaccumulation of fluid within the cyst.