Embolization followed by surgery for treatment of perimedullary arteriovenous fistula causing acute myelopathy

BACKGROUND: Perimedullary arteriovenous fistula (AVF) is rare. There are three subtypes, and the treatment strategies for each are different. Subtype B (multiple fistulas) can be treated by either embolization or surgery. On the basis of a case from our treatment experience, we propose a method for achieving optimal outcome while minimizing nerve injury. CASE DESCRIPTION: A 51-year-old female was admitted to our hospital with acute myelopathy caused by a perimedullary AVF. Initially, we treated her by embolization using the chemical agent Onyx. Her symptoms improved immediately but gradually returned beginning 1 week later. Two months later, the symptoms had returned to pretreatment status, so we removed the fistulas surgically. Severe adhesions between nerve and occult venous varices were noted during the operation. Afterward, the patient's symptoms improved significantly. Histopathological sections showed an inflammatory reaction around the varices. CONCLUSIONS: We initially considered several possible reasons for the return of symptoms: (a) Hypoperfusion of the spinal cord; (b) mass effect of the occult vein varices; (c) residual AVF or vascular remodeling resulting in recurrent cord hypertension; (d) Onyx-induced perivascular inflammation resulting in nerves adhering to each other and to occult venous varices. Clinical, surgical, and pathological findings ruled out the first three, leaving Onyx-induced perivascular inflammation as the probable reason. Given our treatment experience and the pros and cons of the two methods, we propose that initial embolization followed by surgery after 5 days to remove occult venous varices is the ideal strategy for treating perimedullary AVF of subtype B.