Nerve sheath tumors are rare tumors that grow on the lining of nerve cells. Symptoms differ depending on whether the tumors are cranial, spinal, or peripheral. They’re usually benign, but malignant cases may require aggressive treatment.

Nerve sheath tumors are rare tumors that develop on the protective lining (sheath) that surrounds and insulates the nerve fibers. These tumors often form in the arms, legs, and torso, but they can grow in any nerve in the body, including:

  • nerves in your brain (cranial nerves)
  • nerves in your spine (spinal nerves)
  • nerves that connect the spinal cord to the body (peripheral nerves)

Nerve sheath tumors are usually noncancerous (benign) but can sometimes be cancerous (malignant).

Symptoms include pain, numbness, and weakness. You may also feel a lump or mass beneath the skin.

Benign nerve sheath tumors may not require any treatment. Malignant tumors often require surgery and sometimes chemotherapy and radiation.

Nerve sheath tumors can be benign, which means there’s no cancer, or malignant, which means they are cancerous. More than 90% of nerve sheath tumors are benign.

Schwannomas

Schwannomas are benign nerve sheath tumors. Schwannomas grow from cells called Schwann cells. Schwann cells surround and protect the nerve cells of your nervous system.

These tumors usually grow slowly and don’t usually require any treatment. In some cases, they grow large enough to press against the spinal cord or nerves.

The most common type of schwannoma is called a vestibular schwannoma or acoustic neuroma. These tumors grow along the nerves inside the ear, called the vestibular nerves. They sometimes cause hearing and balance problems.

In very rare cases, benign schwannomas can become malignant.

Neurofibromas

Neurofibromas are similar to schwannomas but can grow from:

  • axons
  • perineurial cells
  • Schwann cells
  • fibroblasts of the nervous system

Neurofibromas are usually benign but have a higher risk of becoming malignant compared to schwannomas.

Neurofibromas also include a more aggressive subtype known as a malignant peripheral nerve sheath tumor (MPNST). These tumors can form anywhere but often affect the legs, arms, or pelvis.

Malignant vs. benign nerve sheath tumors

It’s important to understand if your nerve sheath tumor is benign or malignant. Benign means the tumor is not cancerous. Malignant means the tumor is cancerous.

Benign tumors develop slowly. They don’t pose an urgent health risk.

Although rare, malignant nerve sheath tumors grow and spread rapidly and require more aggressive treatment.

Nerve sheath tumors occur due to mutations (changes) in your genes that result in the overactivation of nerve sheath cells. Researchers aren’t sure what causes these mutations to occur. They may happen spontaneously in otherwise healthy people for unknown reasons.

Nerve sheath tumors are sometimes associated with a rare genetic condition called neurofibromatosis. There are three types of neurofibromatosis: NF1, NF2, and schwannomatosis. The risk of a malignant nerve sheath tumor is higher in people with NF1.

Nerve sheath tumors aren’t common. For example, experts estimate that schwannomas occur in fewer than 50,000 people in the United States.

Nerve sheath tumors can occur in people of all ages and genders. Doctors most often diagnose MPNST in people in their 30s.

You may be at a higher risk for nerve sheath tumors if:

  • You had radiation therapy to treat cancer 10 to 20 years ago.
  • You have neurofibromatosis, especially NF1.

According to the National Cancer Institute (NCI), about 8% to 13% of people with NF1 will get MPNST in their lifetime.

The symptoms of a nerve sheath tumor may include:

Schwannomas don’t always cause symptoms.

When to contact a doctor

If you have any symptoms of nerve sheath tumors or if you feel any sort of lump or nodules growing under the skin, schedule an appointment with your doctor. Though rare, MPNSTs are aggressive and spread quickly. It’s important not to delay diagnosis and treatment.

A doctor will conduct a physical exam and ask about your medical and family history. If you have any symptoms of nerve sheath tumors, your doctor will order imaging tests such as an MRI or CT scan.

If the scans reveal a tumor, your doctor may perform a biopsy. During a biopsy, a doctor uses a needle to take a small sample from the tumor. They then send the sample to a lab for testing.

Treatment for nerve sheath tumors depends on where the tumor is in your body and how quickly it’s growing. Treatment options include:

  • Watch and wait: If the tumor is benign and growing slowly, your doctor will monitor it closely during regularly scheduled appointments.
  • Surgery: If the tumor is growing rapidly or causing symptoms, your doctor may choose to remove it with surgery.
  • Chemotherapy and radiation: For malignant tumors, your doctor may use chemotherapy combined with radiation to treat the tumor and keep it from coming back.
  • Rehabilitation: You may need to work with a physical therapist to help you recover from surgery.

Nerve sheath tumors are usually benign, but you might have long-term muscle weakness or hearing loss, depending on the tumor’s location.

There’s a small risk of nerve damage with surgery. A benign tumor is unlikely to grow back after surgery.

MPNST can grow and spread quickly. It may be resistant to chemotherapy and often return after treatment. According to the National Institutes of Health, MPNST has a 65% chance of coming back after surgery (recurrence) and a 40% chance of spreading (metastasis). These tumors may require aggressive treatment for the best outcome.

What is the life expectancy for people with malignant peripheral nerve sheath tumors?

According to the NCI, between 23% and 69% of people with MPNST survive for at least 5 years after diagnosis. But this can depend on many factors, including the size of the tumor. Talk with a doctor to learn more about your specific case.

Nerve sheath tumors include schwannomas and neurofibromas. They are usually benign and may not have any symptoms.

If nerve sheath tumors press against the spinal cord or any nerves, they can cause pain, weakness, hearing loss, or paralysis. If this is the case, talk with your doctor about the risks and benefits of having it removed.

In rare cases, nerve sheath tumors can become cancerous and may require aggressive treatment.