A moderately firm, benign, encapsulated tumor resulting from proliferation of schwann cells and fibroblasts that includes portions of nerve fibers. The tumors usually develop along peripheral or cranial nerves and are a central feature of neurofibromatosis 1, where they may occur intracranially or involve spinal roots. Pathologic features include fusiform enlargement of the involved nerve. Microscopic examination reveals a disorganized and loose cellular pattern with elongated nuclei intermixed with fibrous strands. (From Adams et al., Principles of neurology, 6th ed, p1016)