The peripheral nerve sheath is the soft tissue that covers the nerves traveling out from the brain and spinal cord. Sometimes, tumors develop in this sheath. While nerve tumors can form anywhere in the body and often affect then nerve’s function, most are benign. A malignant peripheral nerve sheath tumor (MPNST), however, can form from peripheral nerve sheath cells or benign peripheral nerve sheath tumors called neurofibromas.
MPNSTs, which account for between 5 and 10 percent of all soft tissue sarcoma cases but less than 1 percent of all peripheral nerve sheath tumors, most often develop in the deep soft tissue along the sciatic nerves, which run from the buttocks to the legs, or the nerves that run for the arms or legs or those within the pelvis. At first, patients often have no or few symptoms, but as the tumors grow they can cause pain or nerve loss.
Malignant peripheral nerve sheath tumor is very rare, appearing in only about 0.001 percent of the population. Individuals who have an inherited condition called neurofibromatosis are at higher risk of developing a nerve tumor, including an MPNST.
Benign peripheral nerve sheath tumors, including the two most common types, schwannomas and neurofibromas, tend to grow slowly and do not spread to other parts of the body. Untreated, however, they may compress the adjacent nerve fibers and cause nerve dysfunction, leading to pain, numbness and/or weakness in the affected peripheral nerve.