Bifid Facial Nerve with Dual Origin Identified During Resection of Vestibular Schwannoma.

Facial nerve identification and preservation is a critical step in the resection of vestibular schwannoma. The use of intraoperative neurostimulation to positively identify the facial nerve along its entire course is essential to prevent injury. To our knowledge, this is the first reported case of a bifid facial nerve with a dual origin at the brainstem, which we observed during resection of vestibular schwannoma via the translabyrinthine approach. Both roots were visualized to join as one facial nerve trunk outside the brainstem in the cisternal segment of the facial nerve, and both trunks demonstrated positive signal with neurostimulation. This case highlights an important anatomic variation and also the importance of correct identification of facial nerve anatomy during resection of vestibular schwannoma and other pathologies within the cerebellopontine angle.