Direct intraoperative confirmation of penetration of ethylene vinyl alcohol copolymer (Onyx) into the vasa nervosa of the facial nerve

The case history is described of a patient referred to our institution with facial nerve palsy following embolization of a middle cranial fossa dural arteriovenous fistula using ethylene vinyl alcohol copolymer (EVOH). Facial nerve decompression was performed which showed evidence of extensive penetration of EVOH into the vasa nervosa of the facial nerve. Facial nerve palsy is a debilitating complication that can be avoided by attention to the lower cranial nerve arterial supply during careful procedural planning and consideration of alternative strategies for fistula obliteration in cases where eloquent feeders are involved.