A schwannoma is a type of nerve tumor of the nerve sheath. It's the most common type of benign peripheral nerve tumor in adults. It can occur anywhere in your body, at any age.

A schwannoma typically comes from a single bundle (fascicle) within the main nerve and displaces the rest of the nerve. When a schwannoma grows larger, more fascicles are affected, making removal more difficult. In general, a schwannoma grows slowly.

If you develop a schwannoma in an arm or leg, you may notice a painless lump. Schwannomas are rarely cancerous, but they can lead to nerve damage and loss of muscle control. See your doctor if you have any unusual lumps or numbness.

To diagnose a schwannoma, your doctor may ask you about signs and symptoms, discuss your medical history, and perform both a general physical and neurological exam. If signs suggest that you could have a schwannoma or other nerve tumor, your doctor may recommend one or more of these diagnostic tests:

• Magnetic resonance imaging (MRI). This scan uses a magnet and radio waves to produce a detailed, 3-D view of your nerves and surrounding tissue.
• Computerized tomography (CT). A CT scanner rotates around your body to record a series of images. A computer uses the images to make a detailed view of your growth so that your doctor can evaluate how it may be affecting you.
• Electromyogram (EMG). For this test, your doctor places small needles in your muscles so an electromyography instrument can record the electrical activity in your muscle as you try to move it.
• Nerve conduction study. You're likely to have this test along with your EMG. It measures how quickly your nerves carry electrical signals to your muscles.
• Tumor biopsy. If imaging tests identify a nerve tumor, your doctor may remove and analyze a small sample of cells (biopsy) from your tumor. Depending on the tumor's size and location, you may need local or general anesthesia during the biopsy.
• Nerve biopsy. If you have a condition such as progressive peripheral neuropathy or enlarged nerves that mimic nerve tumors, your doctor may take a nerve biopsy.

Schwannoma treatment depends on where the abnormal growth is located and whether it is causing pain or growing quickly. Treatment options include:

• Monitoring. Your doctor may suggest observing your condition over time. Observation may include regular checkups and a CT or MRI scan every few months to see if your tumor is growing.
• Surgery. An experienced peripheral nerve surgeon can remove the tumor if it is causing pain or growing quickly. Schwannoma surgery is done under general anesthesia. Depending on the location of the tumor, some patients can go home the day of surgery. Others may need to stay in the hospital for one or two days. Even after successful removal of the tumor during surgery, a tumor may recur.
• Radiation therapy. Radiation therapy is used to help control the tumor growth and improve your symptoms. It may be used in combination with surgery.
• Stereotactic radiosurgery. If the tumor is near vital nerves or blood vessels, a technique called stereotactic body radiation therapy may be used to limit damage to healthy tissue. With this technique, doctors deliver radiation precisely to a tumor without making an incision.