Connections between the facial, vestibular and cochlear nerve bundles within the internal auditory canal

Abstract

The vestibular, cochlear and facial nerves have a common course in the internal auditory canal (IAC). In this study we investigated the average number of nerve fibres, the average cross-sectional areas of the nerves and nerve fibres, and the apparent connections between the facial, cochlear and vestibular nerve bundles within the IAC, using light and scanning electron microscopy. The anatomical localization of the nerves within the IAC was not straightforward. The general course showed that the nerves rotated anticlockwise in the right ear from the inner ear end towards the brainstem end and vice versa for the left ear. The average number of fibres forming vestibular, cochlear, and facial nerves was not constant during their courses within the IAC. The superior and the inferior vestibular nerves showed an increase in the number of nerve fibres from the inner ear end towards the brainstem end of the IAC, whereas the facial and the cochlear nerves showed a reduction in the number of fibres. This suggests that some of the superior and inferior vestibular nerve bundles may receive fibres from the facial and/or cochlear nerves. Scanning electron microscopic evaluations showed superior vestibular-facial and inferior vestibular-cochlear connections within the IAC, but no facial-cochlear connections were observed. Connections between the nerves of the IAC can explain the unexpected vestibular disturbances in facial paralysis or persistence of tinnitus after cochlear neurectomy in intractable tinnitus cases. The present study offers morphometric and scanning electron microscopic data on the fibre connections of the nerves of the IAC.

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

“…However, few reports exist on the connections between the nerves of the internal auditory meatus. Oort [17] was the first to describe a connection within the internal auditory meatus between the vestibular and cochlear nerves, the so-called anastomosis of Oort. Regarding deep connections between the facial and vestibulocochlear nerves, Paturet [18] found connections between the genu of the facial nerve and Scarpa's ganglion.…”

“…Within the internal acoustic meatus, Özdogmus et al [17] reported a connection between the vestibular nerves and facial nerve, but no connections between the cochlear and facial nerves. Nageris et al [16] noted a communication between the facial and vestibular nerves in the temporal bone in 82% of specimens.…”

A Radiological Study on the Topographical Relationships between the Vestibular, Cochlear and Facial Nerves

“…The anatomy of the neural structures in the IAC has been the subject of numerous histological, surgical and radiological investigations owing to its clinical and functional importance [1][2][3][4]7].…”

“…Our findings are in agreement with a previous MRI study reported by Ryu et al but differ from previous cadaver studies. We believe this is due to the distortion of the normal spatial relationships in the A B C absence of cerebrospinal fluid and blood supply as well as the shrinkage of the nerves through formalin fixation and the displacement of the nerves that may have occurred during harvesting of the specimens [1,3,7]. The present study shows that near the brainstem the VCN is most frequently rectangular (60%) or round (31%) in shape but that it changes into a crescent shape in the cerebellopontine cistern when approaching the porus acousticus (89%).…”

“…Along their course from the brainstem to the internal acoustic canal, the relationship between the facial and vestibulocochlear nerves shows some variations [1,2]. With the development of microsurgery and endoscopic surgery in the internal acoustic canal (IAC), the study of the topographical relationship between these two nerves in the human IAC becomes increasingly important for the diagnosis and surgical planning of acoustic schwannomas [2][3][4].…”