Specifics of detecting bone lesions
Due to the loss of elasticity and concomitant severe osteoporosis, the fracture line in an ankylosed vertebra is often difficult to discern. High-quality computed tomography with image analysis in the coronal and sagittal planes is absolutely essential for accurate diagnosis.
A key marker of injury is the vacuum phenomenon. If gas is visualized within the fused spinal structures, it indicates the presence of pathological mobility, which unambiguously confirms a fracture (the mechanism is analogous to the formation of the vacuum phenomenon in the intervertebral disc of a healthy person during movements).
Since ankylosis significantly increases the risk of multilevel fractures occurring simultaneously, the examination protocol requires visualization of the entire spine. MRI is a reliable method for this purpose, especially the STIR (short tau inversion recovery) sequence, which clearly visualizes the fracture zone across the entire width of the bone tissue.
Evaluating neurological prognosis on MRI
Magnetic resonance imaging is the primary tool for predicting functional recovery after spinal cord injury. The localization of the so-called burst fracture relative to the medullary conis (conus medullaris) is of critical importance. If the injury affects structures below the conus—the cauda equina (cauda equina)—the chances of neurological recovery are significantly higher.
The MRI picture allows stratifying the patient's prognosis:
- Favorable prognosis: presence of only mild spinal cord edema.
- Poor prognosis: detection of hemorrhage into the brain substance (meanwhile, hematomas up to 4 mm leave a better chance than large foci).
- Worst prognosis: complete anatomical transection of the spinal cord.
It is also important to remember the risk of delayed complications: late neurological deterioration may be associated with the development of post-traumatic syringomyelia.
Evolution of spinal cord hematoma on MRI
The semiotics of intramedullary hemorrhage on tomograms changes depending on the age of the injury, which requires competent signal interpretation:
- Acute stage: On T2-weighted images (T2-WI turbo spin echo), the hemorrhage zone appears hypointense (yields a low signal). This is due to the presence of deoxyhemoglobin.
- Subacute stage (up to 10 days): As deoxyhemoglobin converts to methemoglobin, the signal becomes hyperintense (high). The glowing zone begins to form from the periphery of the hematoma.
Hemorrhage must be differentiated from traumatic edema. Unlike hematoma, edema yields a uniform hyperintense signal on T2-WI and is typically located below the level of the main hemorrhage. To increase the scanner's sensitivity to blood breakdown products, it is recommended to include gradient echo sequences (gradient echo sequences) in the scanning protocol.
Briefly: answers to topical questions
How does the MRI semiotics of a spinal cord hematoma change depending on the stage of hemorrhage?
The MRI semiotics of a spinal cord hematoma changes from a hypointense signal in the acute stage to a hyperintense signal in the subacute stage.
- Acute stage — on T2-weighted images (T2-WI turbo spin echo), the hemorrhage appears hypointense due to the presence of deoxyhemoglobin.
- Subacute stage — within up to 10 days, the signal becomes hyperintense due to the transition to methemoglobin, with the hyperintensity zone starting to form from the periphery of the hematoma.
To increase sensitivity to the presence of hemorrhage, it is recommended to use gradient echo sequences (gradient echo sequences).
Class and exam questions
Why is scanning the entire spine necessary in ankylosing spondylitis?
Due to the high risk of multilevel injuries. The fused spine behaves like a single long tubular bone during trauma, so fractures can occur in several segments at once.
How to distinguish spinal cord edema from hematoma on MRI?
Edema has a homogeneous high (hyperintense) signal on T2-WI and is usually located below the hematoma zone. Hematoma in the acute stage yields a low (hypointense) signal due to deoxyhemoglobin.
What limitation does MRI have in diagnosing injuries in such patients?
The main limitation is physical. Patients with severe kyphosis in the setting of ankylosis may simply not fit into the bore of a closed MRI scanner.
What else to study on this topic
- Biomechanics of spinal trauma in ankylosing spondylitis
- Physics of the MRI signal: deoxyhemoglobin and methemoglobin in T2-WI
- Differential diagnosis of vertebral burst fractures
- Pathogenesis and radiological picture of post-traumatic syringomyelia
- Specifics of applying gradient echo sequences
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