Seventy of 178 patients with
acoustic tumors initially were treated conservatively and have been followed up for an average of 26 +/- 2 months. The
tumor size was determined by the mean maximum anteroposterior and mediolateral diameters, using computed tomographic or magnetic resonance imaging scans obtained sequentially throughout the follow-up period. The average
tumor growth was 1.6 +/- 0.4 mm the 1st year, and 1.9 +/- 1.0 mm the 2nd year (range, -2 to 17 mm/y): 4
tumors showed apparent regression, 28 (40%) had no detectable growth, and 37 (53%) exhibited growth (average, 3.8 +/- 1.2 mm/y). Within individual patients, the
tumor growth rate determined during the 1st year of follow-up was predictive of
tumor growth rate determined during the following year. Rapid
tumor growth or
clinical deterioration in 9 of the 70 patients (13%) who initially were treated conservatively necessitated subsequent surgery an average of 14 +/- 5 months after the patient was initially seen. This group had a larger initial
tumor size (27.0 +/- 3.4 mm vs. 21.3 +/- 0.9 mm, P less than 0.05), and a faster 1-year growth rate (7.9 +/- 2.3 mm/y vs. 1.3 +/- 0.3 mm/y, P less than 0.05) than the 61 patients who did not require surgery. Two patients, however, experienced neurological deterioration that required surgery, even though there was no
tumor growth. The high incidence of
acoustic tumors with no detectable growth or apparent
spontaneous regression must be taken into account when evaluating the indications for surgery and the efficacy of
radiotherapy.(ABSTRACT TRUNCATED AT 250 WORDS)