Microscopic anatomy of the anastomosis and topographical relationship of nerves in the human internal auditory canal

Objective To investigate the topographical relationship and anastomosis of nerves in the human internal auditory canal. Methods We dissected 30 human temporal bones from 15 heads in order to examine the topographical relationship and anastomosis of nerves in the internal auditory canal. Results (1) In 11 temporal bones, the facial nerves coursed anterosuperior to the vestibulocochlear nerve in the whole portion of the internal auditory canal. In 19 temporal bones, the facial nerves rotated 30° -90° to the anteroinferior direction along the course from the fundus of the internal auditory canal to the porus acusticus, similar to that of the cochlea. (2) Vestibulo-facial anastomosis occurred in 25 cases, of which 67% occurred near the porus acusticus, 33% between the fundus and the intermedial portion of the internal auditory canal. The diameter of the anatomosis was about 0.5 -1 mm. (3) Vestibulocochlear anastomosis occurred in 24 cases, some of which appeared as a brush-like nerve fiber bundle of the cochlear nerve entering the sacculus directly (13 cases). Transverse vestibulocochlear anastomosis in the fundus of the internal acoustic meatus occurred in 15 cases, including 2 cases with more than one anastomoses. No vestibulocochlear nerve anastomosis were found in 6 cases in this study. Conclusion The vestibulo-facial and vestibulocochlear anastomosis exists in the human internal auditory canal. They are heterogeneous, the same as the topographical relationship of the facial and acoustic nerves.