Discussion
We presented a case of a Type IV spinal AV fistula. Spletzler et al.(2002) classified Type IV spinal AV fistula into three types according to size and flow of the fistula: the size, flow, venous tension increasing from Type A to Type C (2). In a study of patients with perimedullary fistulas, the mean duration from the appearance of symptoms to diagnosis was 24.6 months for chronic symptoms and 0.5 months for acute symptoms (3). Similarly, in our case, it was diagnosed within 11 months from the initiation of the symptom.
In a systematic pooled analysis of 213 patients with type IV spinal AV fistula, the annual rate of hemorrhage was found to be 2.5 %; however, for hemorrhagic lesions, the annual rate increased up to 5.6% (4). MRI should be used as the first diagnostic tool when Spinal AVM is suspected. Spinal AVMs are seen as flow voids on T2 weighted MRI and are seen as mixed hypo or hyperintense tubules in T1 weighted MRI depending on their flow velocity and direction (5). However, conventional MRI may have some difficulty in identifying spinal vascular malformation. In a retrospective study, sensitivity and specificity of conventional T2 MRI were found to be 82.8% and 89.4%, respectively, for spinal vascular lesions. Similarly, in another retrospective study, only 53% of cases were reported as spinal vascular malformation in conventional MRI (6). There have been case reports of perimedulary fistulas where conventional MRI has been unable to identify the lesion; as in the case report by Marshman et al. (7), MRI failed to identify flow voids. Also, in the case report by Suntharalingam et al. (8), perimedullary fistula was misinterpreted as a neurinoma. As in our case, it was initially misinterpreted as ependymal myxoma on MRI findings.
Embolization is a viable option for type IV b spinal AV fistula because of the diameter of feeding arteries. But studies have shown that embolization does not provide complete obliteration in all cases, because of which, they may require a surgical approach afterward (9,10).