This 48-year-old female has indicated lower extremity weakness and numbness. Using image 1, can you identify the abnormality?
Dural arteriovenous fistula (AVF), the most common spinal vascular malformation, is evident in image 2 (green arrows). There are just too many hypointense “dots”. Dural AVF account for 65% of all vascular malformations of the spine. These are acquired lesions, and 80% of patients are male averaging around 50 years of age. They frequently complain of back and leg pain with progressive myelopathy from venous hypertension, also known as Foix-Alajouanine syndrome or subacute necrotizing myelopathy. This may accelerate or become more pronounced when there is venous occlusion or thrombosis. The point of fistulization (anastomotic fistula formation) is usually near the intervertebral foramen originating from an intradural radiculomeningeal artery and vein. It is a direct connection between arterial : venous side as opposed to the complex tuft or nidus of an arteriovenous malformation (AVM).
Further imaging findings include (a) serpiginous innumerable filling defects within the subarachnoid space, (b) cord swelling, (c) intramedullary indistinct signal hyperintensity that is contiguous for multiple segments, and (d) mild ill-defined enhancement. Angiographically, either single or multiple feeders from radicular arterial branches are noted. There is usually a single intradural draining vein. A small, yet focal, nidus of arteriovenous shunting is usually noted at the intervertebral foramen.
Unlike many of the other types of arteriovenous malformations, AVFs usually do not present with hemorrhage. The other types of arteriovenous malformations lack a sex predilection (while dAVF of the spine is more common in men), and are likely to present in a younger age. The symptoms of this disease are gradually progressive, unlike multiple sclerosis (a commonly mistaken diagnosis) which is a stuttering waxing and waning syndrome with skip lesions on MRI. If a patient with dAVF (type 1) has a sudden decline, it is usually from venous thrombosis with secondary cord ischemia. This is known as subacute necrotizing myelopathy or Foix-Alajouanine syndrome.
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1. Minami et al. Radiology 1988; 169(1): 109-115