Neural connections between the nervus intermedius and the facial and vestibulocochlear nerves in the cerebellopontine angle: an anatomic study.

Purpose: Unexpected clinical outcomes following transection of single nerves of the internal acoustic meatus have been reported. Therefore, this study aimed to investigate interneural connections between the nervus intermedius and the adjacent nerves in the cerebellopontine angle.

Methods: On 100 cadaveric sides, dissections were made of the facial/vestibulocochlear complex in the cerebellopontine angle with special attention to the nervus intermedius and potential connections between this nerve and the adjacent facial or vestibulocochlear nerves.

Results: A nervus intermedius was identified on all but ten sides. Histologically confirmed neural connections were found between the nervus intermedius and either the facial or vestibulocochlear nerves on 34 % of sides. The mean diameter of these small interconnecting nerves was 0.1 mm. The fiber orientation of these nerves was usually oblique (anteromedial or posterolateral) in nature, but 13 connections traveled anteroposteriorly. Connecting fibers were single on 81 % of sides, doubled on 16 %, and tripled on 3 %, six sides had connections both with the facial nerve anteriorly and the vestibular nerves posteriorly. On 6.5 % of sides, a connection was between the nervus intermedius and cochlear nerve. For vestibular nerve connections with the nervus intermedius, 76 % were with the superior vestibular nerve and 24 % with the inferior vestibular nerve.

Conclusions: Knowledge of the possible neural interconnections found between the nervus intermedius and surrounding nerves may prove useful to surgeons who operate in these regions so that inadvertent traction or transection is avoided. Additionally, unanticipated clinical presentations and exams following surgery may be due to such neural interconnections.