Conservative management of acoustic neurinomas: prospective study of long-term changes in tumor volume and auditory function.

Recently reported retrospective analysis on the natural courses of acoustic neurinomas have disclosed that 26-86% of tumors show very slow, or no, growth for many years. To our knowledge, however, there have been no prospective analyses of the natural course of these tumors. We prospectively analyzed tumor growth as well as auditory function changes in 12 patients (13 tumors) managed conservatively. All 12 patients were advised to undergo both pure tone audiometry and magnetic resonance imaging at 3-4 month intervals for the first follow-up year and at 1-2 year intervals thereafter. Then, in the event of either significant tumor growth (> 20% volume increase) or hearing deterioration (> 10 dB), a decision would be made as to whether the patient should undergo either surgery or radiosurgery. A significant increase in tumor volume was confirmed in seven of the 13 tumors during the mean observation period of 564 days (88-1269 days). In another patient, though neither tumor growth nor worsening of auditory acuity was significant, the patient complained of subjective change in the symptoms. Therefore, we decided to treat eight (62%) of the 13 tumors. In contrast, neither tumor growth nor worsening of auditory acuity has as yet occurred in the remaining five tumors (38%) which have been observed for a mean period of 627 days (342-1377 days). Careful follow-up of these five patients is ongoing. Although further long-term follow-up is clearly necessary, conservative treatment appears to be a reasonable alternative to immediate treatment for selected patients with acoustic neurinomas.