Relative frequency of inferior vestibular schwannoma.

Until quite recently, acoustic tumors were not diagnosed until they had reached relatively large size. Vestibular function tests were positive in a large percentage of these cases. Since vestibular function tests are limited to lesions of the superior branch of the vestibular nerve, it was thought that 90% of vestibular schwannomas arose from the superior vestibular nerve. Recently, as the diagnostic efficiency of auditory tests has improved, many small tumors are being detected. As the size of the tumors decreases, the efficiency of vestibular function testing has also decreased. A review of histologic and surgical literature demonstrates that the earlier estimate is inaccurate, and that only 50% of vestibular schwannomas originate on the superior branch of the vestibular nerve. This warrants a critical review of the value of vestibular function tests in the evaluation of suspected vestibular schwannomas.