De novo Dural Arteriovenous Fistula at the Drainer Site after Embolization of Brain Arteriovenous Malformation.

We report a rare case of de novo ectopic dural arteriovenous fistula (dAVF) that developed late after the endovascular embolization of a brain arteriovenous malformation (AVM). A 25-year-old man with severe chronic headache was diagnosed with an unruptured right frontal AVM located on the medial side of the Sylvian fissure. The AVM was completely occluded using transarterial liquid embolization. However, 12 months after the embolization, the patient developed right pulsatile tinnitus. Angiography revealed a de novo dAVF at the convexity, distant from the original AVM nidus. The dAVF was supplied by multiple dural arteries and a small pial contribution and drained into a cortical vein previously used as the AVM's drainage route. The fistula was successfully treated with additional embolization and radiosurgery. It is well known that large, superficial AVMs tend to involve meningeal arterial supply. However, this case demonstrated delayed ectopic dAVF formation along a draining vein far from the nidus. Although the exact etiology remains unclear, drastic hemodynamic changes in cortical veins previously used as shunt draining route may induce unexpected angiogenesis, leading to the formation of such an unusual de novo dAVF. Even after successful AVM occlusion, long-term follow-up imaging is important, and the possibility of dAVF formation would offer stronger clinical guidance.