Intraparenchymal schwannoma involving the brainstem in a young woman.

Schwannomas are tumors derived from the Schwann cells, which form the myelin sheath of the peripheral nerves. Fewer than 1% of these tumors occur within the brain parenchyma without arising from the cranial nerves. Only 55 cases have been published after the first recorded case. We report a 17-year-old girl with a 3-month history of unspecific dizziness, unsteadiness, and headache. Magnetic resonance imaging showed a heterogeneous cystic lesion involving midbrain, pons, and left cerebellar peduncle. The patient underwent a retromastoid craniotomy with complete resection of the tumor. Pathologic examination was compatible with intraparenchymal schwannoma. Since the first case of intraparenchymal schwannoma involving the brainstem was described in 1980, only seven others have been reported. Diagnosis of intraparenchymal schwannoma is almost never made preoperatively. Immunohistochemical staining is crucial in distinguishing a Schwannoma from a meningioma, glial tumor, or metastatic tumor. Pathologic findings are those typical of acoustic neurinomas. Histogenesis of intraparenchymal schwannoma remains unclear, and several theories have been proposed to explain their origin. The recognition of this curable tumor and its differentiation from brainstem glioma, which generally has a less favorable outcome, is of obvious importance.