Occult schwannomas of the vestibular nerve.

Five small occult schwannomas of the vestibular nerve were discovered on routine examination of 893 serially sectioned temporal bones of 517 individuals. Three arose from the superior division, one from the inferior division, and the other had a multicentric origin from both divisions of the nerve. Location and size of these tumors indicate that clinical diagnosis would have been difficult or impossible by any method of study. The finding of vestibular schwannomas in 0.9% of individuals in this series, indicates the high incidence of this tumor in the general population. The much lower incidence of diagnosed symptomatic tumors in the general population can only be explained by the conclusion that this neoplasm exhibits considerable variation in growth characteristics. Usually the tumor enlarges so slowly as to be of no health importance, but occasionally it grows more rapidly to become symptomatic and require surgical removal.