Clinical risk factor analysis of bilateral vestibular schwannoma's growth pattern inconsistency in individual NF2 patients.

OBJECTIVE Although bilateral vestibular schwannomas (VSs) in individual NF2 patients have the same NF2 gene mutation, they often show different growth patterns. We attempted to identify factors associated with this growth pattern inconsistency. PATIENTS AND METHODS Cranial MR images of 120 untreated VSs in 60 NF2 patients were carefully reviewed for their growth rates. Growth pattern analysis was performed on 68 VSs in 34 NF2 patients followed up for more than three years with at least three cranial MR scans. RESULTS Patient age and tumor volume were significantly associated with NF2 VS absolute growth rates (p < 0.05). Bilateral VS growth patterns in individual NF2 patients were the same in 18 (52.9 %) and different in 16 (47.1 %) patients. Patients with consistent bilateral growth patterns were significantly younger than the inconsistent patients (21.8 ± 5.8 years vs. 30.8 ± 13.1 years, p = 0.014). The bilateral VS volume consistency rates were significantly higher in patients with consistent growth patterns than in patients with inconsistent growth patterns (10/18 vs. 3/16, p = 0.028). CONCLUSIONS Patient age and volume consistency are the clinical risk factors for bilateral NF2 VS growth pattern inconsistencies. Bilateral VSs in young NF2 patients tend to have the same growth patterns. These findings may help us to predict the future clinical behavior of small NF2 VSs based on the past clinical history of the large ones.