Spinal dural arteriovenous fistula and venous aneurysm: an unusual association

OBJECTIVE: Although spinal intradural arteriovenous malformations have frequently been associated with venous aneurysms, spinal dural arteriovenous fistulas typically are not. We describe a case of conus medullaris compression by a large saccular venous aneurysm of a spinal dural arteriovenous fistula. As these lesions are slow-flow arteriovenous shunts, development of a venous aneurysm is an unexpected condition. Pathogenesis of these aneurysms is briefly discussed. METHODS: A 61-year-old man presented with progressive spastic paraparesis of 1-year duration. Spinal magnetic resonance (MR) suggested abnormal serpiginous vessels and a partially thrombosed aneurysm at the level of conus medullaris. Spinal angiography was performed but some lower thoracal and upper lumbar segments could not be catheterized because of severe atherosclerosis. As a result, vascular anomaly could not be demonstrated angiographically, but surgical exploration was found to be necessary because of positive clinical and MR findings. RESULTS: An arteriovenous fistula that entered the spinal canal beneath the L1 pedicle on the left was identified. It was easily coagulated and cut. The partially thrombosed aneurysm within the conus medullaris was also resected. CONCLUSIONS: Our case illustrates two important points related to patients harboring spinal dural arteriovenous fistulas (AVF): First, clinical suspicion and MR findings are important in diagnosis of these lesions and surgical exploration is indicated despite negative or nondiagnostic angiographic results in such cases. Second, venous aneurysms may be associated with spinal dural AVFs, and although spinal dural AVFs are low-flow lesions, the development of the venous aneurysm is probably a result of high venous pressure.