There are a few different types of nerve sheath tumors, also known as peripheral nerve sheath tumors. The most common types of these tumors are benign, schwannoma, and neurofibroma tumors. Malignant, or cancerous, peripheral nerve sheath tumors are called neurofibrosarcomas and are very rare.
Nerve sheath tumors affect the peripheral nervous system, which is the part of the central nervous system that connects the nerves in the rest of the body to the spinal cord and brain. The tumors develop on the cells that surround the nerves. These tumors most commonly affect the arms and legs.
Schwannomas are one type of nerve sheath tumor. They are composed of schwann cells, which are the cells that make up the protective nerve covering. These are almost always benign tumors. Less than 1 percent of schwannoma tumors become cancerous. The tumors are not harmless, however, and may cause nerve or bone damage as they grow and push against nerve fibers.
Another type of nerve sheath tumors are neurofibromas. Like schwannoma tumors, neurofibroma tumors are typically benign and made up of schwann cells. The schwann cells in these tumors, however, exhibit balletic inactivation of the neurofibromatosis gene, which basically means there is a slight genetic difference. Another difference between schwannomas and neurofibromas is that the former are made of only schwann cells, whereas neurofibromas are formed with many different types of cells.
Schwannomas and neurofibromas can develop into a malignant peripheral nerve sheath tumor. This is called a neurofibrosarcoma. Fortunately, the chances of developing this cancerous tumor are quite rare. They usually form in the deep soft tissue, most commonly occurring in the sciatic nerve, sacral plexus, and brachial plexus. Neurofibrosarcomas are typically diagnosed from a biopsy after the patient expresses symptoms of pain.
The exact cause of nerve sheath tumors remains unknown. They are usually found in individuals with the genetically inherited disease neurfibromatosis. Tumors are treated with surgery, and if cancerous, they are treated with chemotherapy and sometimes radiation. Even when all traces of nerve sheath tumors have been removed, there is always a chance of regrowth.
Humans are not the only animals affected by nerve sheath tumors. These types of tumors have been found in dogs and some types of fish. These tumors, however, are much more common in humans than other animals. Dogs usually develop these tumors late in life, whereas humans are diagnosed at the average age of 35.