ABSTRACT
Schwannomas are benign neoplasms comprised of Schwann cells within the nerve sheath. These tumors are typically encapsulated and form discrete masses that sometimes encircle but do not invade the adjoining nerve. Schwann cells are the principle cells of the peripheral nervous system (PNS). Derived from the neural crest, the neural crest cells migrate to their eventual target in the PNS during embryologic development. Schwannomas are generally found as sporadic, solitary lesions. Multiple schwannomas may occur in the setting of NF2 or schwannomatosis. The etiology of schwannomas is unknown, with some theories as to causative factors, including trauma, chronic irritation, and radiation exposure. Schwannomas in NF2 characteristically involve the eighth cranial nerve in the cerebellopontine angle, classically with bilateral tumors. The overwhelming majority of schwannomas are encapsulated masses measuring less than 10 cm. They are typically of light tan color with intermittent bright yellow cysts; hemorrhage and necrosis may be present.
