Atypical and low-grade malignant vestibular schwannomas: Clinical implications of proliferative activity

Objective: To examine the relationship between histopathology, immunohistoc hemistry, and clinical behavior in atypical and low-grade malignant vestibu lar schwannomas. Study Design: The study design was a retrospective case review in conjuncti on with a histopathologic and immunohistochemical proliferation marker stud y of archival specimens. Data Sources: A tertiary referral center's anatomic pathology and vestibula r schwannoma computerized databases. Methods: The diagnosis of atypical or low-grade malignant vestibular schwan noma was based on the number of mitotic figures present per tumor slide. MI BI labeling indices were used to compare the proliferative activity of the atypical and low-grade malignant groups with that in an age-matched and siz e-matched control group. Results: Eight cases of atypical and six cases of low-grade malignant vesti bular schwannoma were diagnosed from 1990 to 1998. In the atypical and low- grade malignant groups, respectively, the average patient age was 54.3 year s (range, 38-74 yr) and 50 years (range, 38-72 yr), and the average total t umor size was 1.53 cm (range, 0.7-3.5 cm) and 1.55 cm (range, 1.5-2 cm). Tw o recurrences were identified from the low-grade malignant group, and there was one postoperative House-Brackmann Grade III facial weakness. There wer e no recurrences or facial palsies in the atypical group. No distant metast asis or aggressive local invasion was observed in either group. MIBI labeli ng indices were significantly (p less than or equal to 0.001) higher in the atypical (4.69%) and low-grade malignant (5.23%) groups than in the contro l group ( 1.99%). Conclusions: These findings suggest a tendency for recurrence in proliferat ive tumors; however, the designation of malignancy should be reconsidered. Key Words: Vestibular schwannoma-Malignancy-Prolife ration markers.