3.2 | Characteristic imaging findings of SDAVF
In this case, the key to diagnosis was finding abnormal signals in the conus medullaris on lumbar spine MRI (Figure 1b).
The most sensitive MRI finding in SDAVF is venous congestion of the spinal cord, with reported sensitivity rates of up to 100%4. Most patients with SDAVF show high signal intensity with peripheral low signal intensity of the spinal cord on T2-weighted MRI 5. Venous congestion is distributed from the lower thoracic spinal cord to the conus medullaris, regardless of the level of the fistula 6. Even if the fistula is located at the thoracic level, lumbar MRI may show venous congestion of the conus medullaris.
Dilated spinal cord veins in the subarachnoid space are a very specific finding in patients with SDAVF. The specificity of high signal intensity on T2-weighted MRI and flow voids is 97% 4, 7. Although venous congestion may mimic intramedullary tumors, myelitis, syringomyelia, or demyelinating diseases of the spine, the presence of dilated veins may differentiate SDAVF from other conditions that mimic SDAVF 8, 9. T2-weighted MRI shows these abnormal vessels as flow voids around the spinal cord. In some patients with SDAVF, MRI does not show flow voids. However, MDCTA and contrast-enhanced MRA with gadolinium can help identify abnormal vessels around the spinal cord 10, 11. Even lumbar MRI can identify venous congestion and flow voids at the conus medullaris 12). If conus medullaris lesions are evident on a lumbar MRI, a thoracic MRI should be performed to verify the presence of venous congestion around the spinal cord and assess vascular flow voids near the cord.