This slow-growing type of tumor develops on the protective sheath around nerves, usually in the peripheral nervous system. They’re generally not life-threatening, but they require ongoing monitoring and treatment to manage.

Every nerve in your body is protected by a layer of tissue called a sheath. A schwannoma is a tumor that grows in the sheath around the nerves in your peripheral nervous system, or the parts of your nervous system that aren’t in your brain or spinal cord.

Schwannomas are usually benign, meaning they’re non-cancerous. In rare cases, they can be malignant, or cancerous.

In some cases, schwannomas may be referred to as neuromas, neurinomas, or neurilemmomas.

Most people with schwannomas only have a single tumor, but it’s possible to have more. Multiple schwannomas are usually a result of a genetic condition such as neurfibromatosis 2 (NF2) or schwannomatosis.

Schwannomas usually don’t produce symptoms until they become large enough to put pressure on the nerves around them. Some common symptoms of schwannomas include:

  • pain in the area that controlled by the affected nerve
  • a visible lump under the skin
  • sharp, aching, or burning pain
  • a pins-and-needles sensation
  • muscle weakness
  • numbness

You may experience these symptoms in different areas of the body based on where the schwannoma is located. Your symptoms may also change as the tumor grows slowly over time.

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 issues in one hear
  • ringing or buzzing sounds in your ear
  • dizziness
  • balance issues
  • headaches

Most schwannomas are caused by a genetic mutation that causes cells in the sheath around the nerves in the peripheral nervous system to grow uncontrollably. Often, this happens spontaneously with no known cause.

However, in some cases, schwannomas are linked to specific genetic conditions, such as:

  • neurofibromatosis 2 (NF2), which involves mutations to the NF2 gene and that cause multiple schwannomas
  • schwannomatosis, which involves mutations to the LZTR1 or SMARCB1 genes that can cause multiple schwannomas

Diagnosing schwannomas is hard because their symptoms are similar to those of many conditions. They also grow very slowly, so any symptoms they do produce are usually very subtle if they’re even noticeable.

If you do have symptoms, your doctor will perform tests to pinpoint the affected area, such as:

  • magnetic resonance imaging (MRI) scan
  • ultrasound
  • CT scan

They may also give you a hearing and balance test if they think you may have an acoustic neuroma.

Schwannomas are typically benign, or non-cancerous, which means they’re not dangerous. However, depending on where they grow, they may still cause issues.

Most problems caused by schwannomas are the result of the tumor becoming large and putting pressure on nearby nerves. This can cause symptoms like pain, numbness, weakness, or hearing issues.

In very rare cases, a schwannoma can become malignant, but this is not common.

While most schwannomas are not life-threatening, they may need ongoing monitoring and treatment to manage.

Treatment for schwannomas depends on their size, location, symptoms, and growth rate. Options include:

  • watchful waiting, where doctors monitor slow-growing schwannomas for potential problems over time
  • surgery, where schwannomas that cause issues are fully or partially removed
  • radiation, which can be given to slow or stop tumor growth
  • symptom management, which may include pain medication

In the rare case that a schwannoma becomes cancerous, it may need additional treatment.

The outlook for people with schwannomas depends on factors such as the tumor’s:

  • location
  • size
  • response to treatment

Keep in mind that most schwannomas are harmless and may never produce any symptoms. Just make sure to tell your doctor if you do experience any new or changing symptoms.

A schwannoma is a slow-growing tumor that develops on the protective sheath around nerves, usually in the peripheral nervous system. Most schwannomas are not cancerous. However, they can still cause pain, numbness, or other problems if they press on nearby nerves.

Schwannoma treatment may include watchful waiting, surgery, or radiation. Most people with schwannomas have a positive outlook.