Facial Nerve Schwannomas Mimicking as Vestibular Schwannomas.

 The objective of this study was to identify preoperative and intraoperative findings that may aid in distinguishing facial nerve schwannomas (FNS) from vestibular schwannomas (VSs), particularly in cases limited to the internal auditory canal (IAC) and cerebellopontine angle (CPA).  This was a retrospective study.  This study was set at a Tertiary Referral Center.  Seventeen cases from October 2002 to July 2015 with an IAC/CPA mass presumed to be a VS who were found to have a FNS intraoperatively.  The main outcome measures included preoperative presentation, intraoperative findings, and subsequent intervention.  Preoperative hearing loss and imbalance were seen in 70.5 and 64.7%, respectively. Suspicious intraoperative findings included: facial nerve incorporated intimately with the tumor capsule in 12 cases; spontaneous action potentials noted while drilling the bony IAC in 3 cases; and action potentials noted on stimulation of the entire tumor capsule in 10 cases. The mean long-term facial function was House-Brackmann grade II and the mean length of follow-up was 4.86 years.  FNSs are rare and may be difficult to distinguish from VS preoperatively. Surgical findings that should raise concern include spontaneous action potentials during drilling the bony IAC, absence of a plane of dissection between the facial nerve and tumor, or stimulation of the tumor capsule.