Asymptomatic spinal dural arteriovenous fistulas: pathomechanical considerations.

OBJECT: Spinal dural arteriovenous fistulas (SDAVFs) consist of a shunt with converging feeding vessels arising from radiculomeningeal arteries and draining retrogradely via a radicular vein into the perimedullary veins, thereby causing progressive myelopathy due to venous hypertension in the spinal cord. The purpose of this study was to evaluate the hypothesis that the obstruction of radicular venous outlets could be an additional factor inducing symptomatic venous hypertension due to a decreased outflow in SDAVFs.

METHODS: The authors compared the clinical and imaging findings in patients with asymptomatic SDAVFs identified incidentally at the upper thoracic region with the findings in symptomatic patients who harbored SDAVFs at the same level.

RESULTS: All symptomatic patients presented with medullary dysfunction. The mean age of patients with asymptomatic SDAVF was 51.5 years, approximately 10 years younger than the patients with symptomatic SDAVF (64.1 years old). Despite the existence of dilated perimedullary vessels in the dorsal side of the spinal cord in all patients, the spinal cord edema seen in symptomatic patients was not detected on the MR images obtained in patients with asymptomatic SDAVF. The spinal angiograms of the asymptomatic patients distinctively demonstrated early radicular venous outflow from affected perimedullary veins to the extradural venous plexus as a potential alternate route for the venous hypertension to be released.

CONCLUSIONS: Obstruction of the radicular venous outflow could be an important factor in inducing spinal congestive edema due to venous hypertension, as well as subsequent clinical symptoms of SDAVFs.