context: Schwannomas and neurofibrosarcomas are nerve sheath tumors, which means they involve the coating around nerve fibers that transmit messages to and from the brain and spinal cord (nervous system) and the rest of the body. Schwannomas are most often nonmalignant tumors. Neurofibrosarcomas are malignant tumors. Schwannomas form in the tissue that surrounds and insulates nerves. Schwannomas develop when schwann cells -- the cells that form the covering around nerve fibers -- grow abnormally. Schwannomas typically develop along nerves of the head and neck. A type of schwannoma called vestibular schwannoma (or acoustic neuroma) affects the nerve that connects the brain to the inner ear, which can affect your sense of balance. Although schwannomas do not spread, they can grow large enough to press down on important structures in the brain (including the brain stem). A very small percentage of nerve sheath tumors are malignant. These are known as malignant peripheral nerve sheath tumors, or neurofibrosarcomas. Because neurofibrosarcoma originates in nerves, it is considered part of a group of cancers called soft tissue sarcomas. Soft tissue sarcomas are uncommon. They make up less than 1% of all cancers diagnosed each year. Neurofibrosarcomas account for only a small number of these soft sarcomas. Neurofibrosarcoma is usually found in the arms and legs. However, it also can affect the lower back, head, or neck. Neurofibrosarcomas can spread along the nerves. They typically don't reach other organs, although they can spread to the lungs. Doctors don't know what causes most schwannomas and neurofibrosarcomas. However, nerve sheath tumors are more common in people who have the inherited disorder, neurofibromatosis type 1 (previously known as von Recklinghausen disease). Vestibular schwannomas are linked to neurofibromatosis type 2. Having a genetic disorder called schwannomatosis also can increase the risk for schwannomas. A small percentage of neurofibrosarcomas are related to past radiation exposure. Nerve sheath tumors are usually diagnosed when people are between the ages of 30 and 50, although these diseases can sometimes affect children and elderly people. Symptoms of schwannomas can include: A painless or painful growth or swelling on the face Hearing loss or ringing in the ear (vestibular schwannoma) Loss of coordination and balance (vestibular schwannoma) Numbness, weakness, or paralysis in the face Symptoms of neurofibrosarcomas can include: Swelling or a lump in the arms or legs Pain or soreness Difficulty using the arms, legs, feet, or hands Doctors diagnose nerve sheath tumors by doing a physical and neurological (brain and nervous system) examination. Usually they'll also perform imaging tests such as CT or MRI scans to pinpoint the location and size of the tumor. A biopsy (removing a tissue sample and examining it in the lab) can confirm whether the tumor is malignant. Schawnnomas may not need treatment if they are not causing any symptoms. Surgery is sometimes needed if the tumor is pressing on a nerve causing pain or other problems. The most common treatment for neurofibrosarcomas is to remove them with surgery. Radiation therapy is often used after surgery to help decrease the risk of recurrence. However, surgery can be difficult if the tumor is very close to or surrounding an important nerve, because the surgeon could damage the nerve while trying to remove the tumor. In addition to surgery and radiation therapy, chemotherapy may also be needed. When a tumor can't be removed, high-dose radiation therapy may be used to target the tumor. With neurofibrosarcomas, the doctor will remove the tumor and the tissue around it. Surgeons will try to remove the tumor without damaging too much of the affected arm or leg (called limb-salvage or limb-sparing surgery), but if the tumor can't be removed, the arm or leg might need to be amputated. Radiation and chemotherapy may be done before surgery to shrink the tumor so it can be removed more easily, or after surgery to kill any cancer cells that are left behind. Schwannomas usually don't come back if they are removed completely. The prognosis after treatment for neurofibrosarcoma depends on the size of the tumor, where it is located, and how far it has spread. Long-term survival can vary from person to person. It's possible for the cancer to return, even after aggressive treatment.