gms | German Medical Science

Objective: A split course of the facial nerve in vestibular schwannoma surgery was recently published. In a large surgical series of 241 patients 7% split nerves were identified. A prospective study was undertaken evaluating the split nerve phenomenon in a consecutive series.

Methods: Between 7/2005 and 9/2006 31 patients underwent surgery for vestibular schwannomas. 27 patients underwent primary surgery and were included into the study. Evaluation was based on a differentiated multi channel EMG recording set up with at least three EMG channels and separate recordings from the orbicularis oris - oculi and nasal muscle. Intraoperative video screen shots were used for documentation.

Results: The average tumor size measured 26 mm ranging from 15 to 45 mm. Total resection was achieved and documented in all patients. In 14 patients, a split facial nerve was clearly documented. The major portion supplying all three branches of the nerve was located on the ventral tumor surface; the minor portion usually carried fibers exclusively for the orbicularis oris muscle. It followed the presumed superior vestibular nerve on the tumor surface facing the brainstem, crossed the CPA dorsal to the motor fibers of the trigeminal nerve and realigned with the major portion at the porus.

Conclusions: The split nerve phenomenon deserves particular attention in vestibular schwannoma surgery, since clinically a weakness of the orbicularis oris muscle is usually observed initially after surgery. The course of the minor portion was stereotype and reproducible and resembles the course of the nervus intermedius. Identification can be achieved using multi channel EMG monitoring.