What is the site of origin of cochleovestibular schwannomas?

Abstract

The belief that cochleovestibular schwannomas arise from the glial-Schwann cell junction has repeatedly been quoted in the literature, although there is no published evidence that supports this statement. A systematic evaluation of the nerve of origin and the precise location of cochleovestibular schwannomas using our respective archival temporal bone collections was conducted. Forty tumors were within the internal auditory canal (IAC), while 10 were intralabyrinthine neoplasms. Of the 40 IAC schwannomas, 4 arose from the cochlear nerve, and 36 from the vestibular nerve. Twenty-one tumors clearly arose lateral to the glial-Schwann cell junction, while 16 tumors filled at least two thirds of the IAC, with the epicenter of the neoplasm located in the mid part or the lateral part of the IAC. Only 3 schwannomas were located in the medial one third of the IAC in the area of the glial-Schwann cell junction. We concluded that cochleovestibular schwannomas may arise anywhere along the course of the axons of the eighth cranial nerve from the glial-Schwann sheath junction up until their terminations within the auditory and vestibular end organs.

Fig. 1

a, b Low- and high-power views of the glial-Schwann cell junction from a 53-year-old man. c–g Examples of small schwannomas within the IAC, arising in the mid or lateral parts of the IAC. In c and d, the schwannomas are seen to be clearly lateral to the glial-Schwann cell junction. The schwannomas in e–g were also arising lateral to the glial-Schwann cell junction, as determined by examination of serial sections. h Example of a schwannoma filling the medial two thirds of the IAC. The epicenter of the tumor is in the mid portion of the IAC.