Aggressive vestibular schwannomas with postoperative rapid growth: Clinicopathological analysis of 15 cases

OBJECTIVE: Vestibular schwannomas (VSs) are known to be relatively slow-growing tumors. Some VSs, however, rapidly regrow or recur after surgical resection. Our objective was to investigate the clinicopathological characteristics of these tumors and to elucidate factors that can predict rapid regrowth or recurrence after surgical resection. METHODS: Between 1978 and 2000, 29 patients with VS underwent reoperation for regrowth or recurrence at the Department of Neurosurgery in Seoul National University Hospital. Among these patients, 15 experienced rapid VS regrowth or recurrence (annual growth rate, >15 mm/yr). The clinical, radiological, operative, and pathological findings were reviewed. For a comparison of the morphology and proliferative activity, 15 cases of VS were randomly selected as a control group from among the consecutive operative cases with tumor size larger than 4 cm treated between 1991 and 1999. Pathological parameters consisting of cellularity, pleomorphism, mitosis, necrosis, invasion to adjacent tissue, and microvascular proliferation were analyzed. Proliferative indices (e.g., Ki-67 index) also were evaluated. Statistical analyses were performed using Fisher's exact test and the analysis of variance test. RESULTS: The differences in clinical features between the aggressive VS group and the control VS group were nonspecific. The mean ages at diagnosis were 40.6 years (range, 21-63 yr) and 49.7 years (range, 35-67 yr) (P = 0.438), and the male-to-female ratios were 7:7 and 5:10 (P = 0.462), respectively. The clinical symptoms and signs were similar between the two groups. Radiologically, aggressive tumors at initial presentation had more lobulating contours than those in the control group (7 of 13 cases versus 3 of 15 cases; P = 0.001). In pathological findings, cellularity and pleomorphism were significantly higher than those in the control group (P = 0.001). However, mitosis, necrosis, invasion to adjacent tissue, and microvascular proliferation were not different between the two groups. The proliferative index (Ki-67 index) was higher in the aggressive group than in the control group (2.28 [range, 0.1-8.6] versus 0.59 [range, 0-1.5]; P= 0.034). CONCLUSION: VSs presenting with lobulating contour, high proliferative index (Ki-67 index), and high cellularity or pleomorphism require frequent radiological investigation during follow-up to facilitate early detection of regrowth or recurrence.