A 32-year-old male with brainstem lesions.

Schwannosis is a condition characterized by a benign proliferation of Schwann cells and an incomplete myelination of central nervous system axons following different chronic stimuli. It. has been mainly observed in the spinal cord. Various hypotheses have been put forward with respect to the appearance of Schwann cells inside the central nervous system since they exclusively populate the peripheral nervous system. According to these hypotheses, schwannosis seems to be either the result of aberrant migration under certain conditions, especially in response to spinal cord injury, or as a developmental abnormality in form of ectopia during ontogenesis.We report, for the first time, on the multifocal occurrence of this rare nosological entity in the brain stem. Furthermore we compare the histological and immunohistochemical profile of schwannosis to that of an intracerebral schwannoma taken from our archive.