Spatial distribution and postoperative changes in intramedullary lesions caused by spinal dural arteriovenous fistulas of the thoracic cord : Case report

Objective : Spinal dural arteriovenous fistulas (AVFs) represent a rare but important cause of myelopathy brought about by venous hypertension due to shunt formation between the dural artery and medullary vein. Magnetic resonance imaging (MRI) findings include intramedullary hyperintensity on T2-weighted images, as well as cord enlargement due to venous hypertension. Postoperative resolution patterns of hyperintensity suggest a pathophysiology of spinal dural AVF. Clinical presentation and results : We report two cases of thoracic spinal dural AVF with a single feeding artery, which were treated by surgical intervention. MRI findings were reviewed before and after surgery. Before surgery, hyperintensity on T2-weighted images spread from above the feeding artery to the conus, and was present in the central cord on axial images. After correction of the arteriovenous shunt, the region of hyperintensity began to resolve from the cranial side followed by the caudal side. Conclusion : Hyperintensity on T2-weighted images of the cord was largely reversible, indicating that edema of the cord was caused by elevated venous pressure. The hyperintensity on T2-weighted images decreased initially from the cranial side and then from the caudal side. This transmission and resolution of increased venous pressure appeared to depend on the presence of obstruction to the venous outflow system of the spinal cord.