Schwannomatosis: a new member of neurofibromatosis family.

Background: Schwannomatosis is a recently recognized peripheral nerve polyneoplasm with clinical characteristics and a genetic background that differ from those of neurofibromatosis 2 (NF2). The diagnostic and treatment criteria of this rare disorder are herein discussed.

Methods: The data of 180 patients who underwent operations for benign schwannomas from 2003 to 2012 in our center were reviewed. Eight of them were classified as schwannomatosis according to the diagnostic criteria suggested by MacCollin. The demographic characteristics were documented and compared between the two groups of patients. The patients' clinical presentations, imaging characteristics, histological features, and treatment results were retrospectively investigated and summarized.

Results: Of the 180 cases of benign schwannomas we reviewed this time, eight patients presented with schwannomatosis (4.44%). The mean age of the two groups was not significantly different (40.0 vs. 44.7 years, t = 0.88, P = 0.378). However, schwannnomatosis seems to more generally occur in females (75% vs. 48% were females, P = 0.162), although the difference was not statistically significant. The initial main symptom was pain. The neurological examination was otherwise normal. Magnetic resonance imaging (MRI) revealed multiple discrete, well-defined round, or oval lesions distributed along the course of the peripheral nerves in the extremities with low-to-intermediate signal intensity on T1-weighted images and high-signal intensity on T2-weighted images. Vestibular schwannomas were excluded in four patients by cranial MRI. The lesions in all patients were resected and were pathologically proven to be schwannomas. The average follow-up period was 26 months. Six individuals obtained a good result without symptoms or function loss.

Conclusions: Schwannomatosis is characterized by the development of multiple schwannomas without evidence of the vestibular tumors that are diagnostic for NF2. It commonly occurs in middle-aged females. It has similar demographic features to solitary benign schwannoma. Surgical resection always results in a good outcome.