A rare tumor of cranial and spinal nerves arising from peripheral nerve sheath and composed exclusively or predominantly of cells showing perineurial differentiation. It presents as a localized, tubular or fusiform enlargement of a nerve or nerve segment, usually in the extremities or the trunk, associated with a motor-predominant mononeuropathy including slow, painless, gradual loss of motor function in the involved nerve trunk with muscle weakness and atrophy and, rarely, sensory dysfunction. Cranial nerve involvement is rare. [from
SNOMEDCT_US]