Intraoperative Facial Nerve Monitoring Revealed the Origin of Rapidly Progressing Schwannoma in the Cerebellopontine Angle: A Case of Large Intermediate Nerve Schwannoma.

Schwannoma arising from the intermediate nerve is very rare, with only a few cases reported in the literature. Here, we report a rare case of a rapidly glowing schwannoma that originated from the intermediate nerve in a 17-year-old woman. We performed tumor resection using the tanslabyrinthine approach with continuous intraoperative monitoring, in which the facial nerve loot was used to evoke muscle action potential. The monitoring revealed the tumor origin and enabled complete surgical resection with the preservation of facial nerve motor function. The facial nerve loot evoked muscle action potential-based continuous monitoring revealed the origin of the rare intermediate Helve schwannoma. Appropriate surgery using this monitoring system could spare facial nerve function even in this !are case and retain the patient's quality of life.