A hemorrhagic complication after Onyx embolization of a tentorial dural arteriovenous fistula: A caution about subdural extension with pial arterial supply

We report a case of tentorial dural arteriovenous fistula (DAVF) with a severe intracranial hemorrhage occurring after Onyx embolization. A 40-year-old man presented with an asymptomatic tentorial DAVF on angiography. Transarterial embolization with Onyx was performed via the middle meningeal artery, and the cast filled the fistula itself and its proximal draining vein. Postoperative angiography confirmed complete occlusion of the DAVF. A computed tomography scan performed immediately after the procedure demonstrated an acute subdural hematoma with the temporal hemorrhage. Emergency craniotomy revealed continuous arterial bleeding from a viable glomus-like vascular structure around the proximal part of the embolized draining vein, fed by a pial artery arising from the posterior cerebral artery. Pathologic findings suggested diagnosis of vascular malformation extending into the subdural space. Tentorial DAVFs can extend to the subdural space along their drainage route, and may be involved in severe hemorrhagic complications of curative endovascular treatment using Onyx, particularly those with pial arterial supply.