The topographical relationships and anastomosis of the nerves in the human internal auditory canal.

Introduction: The anatomy of the nerves in the human internal auditory canal (IAC) has been reported by a number of authors, and there are some differences among the viewpoints of the literatures. With the development of the microsurgery and endoscopic surgery in the IAC, the study of the topographical relationship of the nerves in the human IAC becomes more and more important. The purpose of this study was to investigate the anastomosis and topographical relationship of the nerves in the human IAC.

Methods: In this study, we dissected 30 human temporal bones from 15 heads, and examined the topographical relationship and the anastomosis of the nerves in human IAC.

Results: (1) In 11 out of 30 cases (37%), the facial nerve is anterosuperior to the vestibulocochlear nerve through the whole IAC; and for the remaining 19 cases (63%), the facial nerve rotates anteroinferiorly at an angle ranging from 30 degrees to 90 degrees , which is in the same direction as that of the cochlear. (2) Vestibulofacial nerve anastomosis occurs in 25 cases (83%), of which 67% appears near the porus acusticus, and of which 33% appears between the lateral and intermedial portion of IAC. The diameter was about 0.5-1 mm. (3) Vestibulocochlear anastomosis occurs in 24 cases (80%) among which, some brush-like nerve fiber bundles of the cochlear nerve were seen to enter the acculus proprius directly in 13 cases. Transverse vestibulocochlear anastomosis in the fundus of internal acoustic meatus occurred in 15 cases, including two cases with more anastomosis. No vestibulocochlear nerve anastomosis was found in six cases in this study.

Conclusions: Our study shows that the Vestibulofacial nerve anastomosis and the vestibulocochlear nerve anastomosis do exist, and some variations appear due to individual differences. The appearance of the facial and vestibulocochlearnerves is variable but follows certain consistent patterns.