Every nerve in your body is protected by a layer of tissue called a sheath. A schwannoma is a tumor that grows in the sheaths of nerves in your peripheral nervous system, or the parts of your nervous system that aren’t in your brain or spinal cord. You may hear schwannomas referred to as neurilemomas, neuromas,or neurolemomas.

Schwannomas are usually benign, meaning they’re harmless. In rare cases, they can be malignant, or cancerous. Malignant schwannomas are also called soft tissue sarcomas.

Most people with schwannomas only have one, but it’s possible to have more. Multiple schwannomas are usually a result of schwannomatosis.

This is the least common type of a rare condition called neurofibromatosis, a genetic disorder that causes tumors in the nervous system. Another form, called neurofibromatosis type 2 (NF2), can also cause schwannomas.

What does a schwannoma feel like?

Schwannomas usually don’t produce symptoms until they become large enough to put pressure on the nerves around them. You may feel occasional pain in the area that’s controlled by the affected nerve. Some other common systems include:

a visible lump under the skin
sharp, aching, or burning pain
a pins-and-needles sensation
muscle weakness
nighttime pain in back or neck

Depending on where the schwannoma is, you may feel these symptoms in your face, arms, legs, or torso. Your symptoms may change as the tumor gets bigger.

Many schwannomas occur on the nerve that connect your inner ear and brain. This is known as a vestibular schwannoma, or acoustic neuroma. In addition to the symptoms above, an acoustic neuroma can also cause:

hearing problems in one or both ears
ringing in one or both ears
loss of coordination and balance

What causes schwannomas?

Aside from NF2 and schwannomatosis, researchers don’t know what causes schwannomas. People with a family history of spinal cancer are more likely to have a spinal schwannoma, which suggests they could be genetic. Exposure to radiation is another possible cause.