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).