Sublocalization and volumetric growth pattern of intracanalicular vestibular schwannomas

Objective. None of several previous reports on the growth pattern of vestibular schwannomas (VS) have dealt with the sublocalization and volumetric growth pattern of intracanalicular tumors. This paper reports such data from 196 patients. Study Design: All VS patients have been registered prospectively at one center in Denmark since 1975. Data on intracanalicular tumors were drawn from the database, yielding 196 patients with a diagnostic and at least one control magnetic resonance imaging scan. All images were retrieved and the tumor sublocalization, size, and growth rate determined. Results: The majority (50%) of the tumors was located centrally in the internal auditory canal (IAC), whereas 31% were porus-near and 19% fundus-near. Of the 196 tumors, 88 (45%) displayed growth, 20 (10%) shrinkage, and 88 (45%) remained unchanged. Thirty-eight (19%) tumors grew to extrameatal extension. Growth occurred only within 5 years after diagnosis. In the 88 growing tumors, the mean absolute growth rate was 111mm (3)/year and the relative rate 114%/volume/year. The occurrence of IAC expansion at diagnosis was higher for tumors displaying subsequent shrinkage. Growth occurrence and rate, IAC expansion, and progression to extrameatal extension were not related to tumor sublocalization. Conclusion: Most intracanalicular VS are located centrally in a nonexpanded IAC at diagnosis. Growth occurs within 5 years after diagnosis in up to 45% of the tumors, although only 19% extend into the cerebellopontine angle. IAC expansion, growth occurrence, and rate are not related to tumor sublocalization. These findings justify primary observation of all purely intracanalicular tumors, unless realistic hearing preservation is intended.