1) A neoplasm that arises from Schwann cells of the cranial, peripheral, and autonomic nerves. Clinically, these tumors may present as a cranial neuropathy, abdominal or soft tissue mass, intracranial lesion, or with spinal cord compression. Histologically, these tumors are encapsulated, highly vascular, and composed of a homogenous pattern of biphasic fusiform-shaped cells that may have a palisaded appearance. (From DeVita Jr et al., Cancer: Principles and Practice of Oncology, 5th ed, pp964-5)

2) A tumor of the peripheral nervous system composed of neoplastic Schwann cells. The vast majority of Schwannomas follow a benign clinical course. Only rare cases associated with a malignant clinical course have been reported. -- 2004

3) A tumor of the peripheral nervous system that arises in the nerve sheath (protective covering). It is almost always benign, but rare malignant schwannomas have been reported.