Nerve Sheath Tumors

Nerve sheath tumors are rare growths that start in tissue surrounding your nerves. Nerves transmit electrical signals between your brain and the rest of your body. Connective tissue and a membrane called the myelin sheath insulate and protect your nerves. (Imagine the plastic covering surrounding the wires of an electrical cord.)

These tumors form in the layers of the insulation. Most nerve sheath tumors form in your peripheral nervous system (PNS). Your PNS includes all the nerves in your body that carry signals to and from your spinal cord and brain.

Most nerve sheath tumors are benign (noncancerous). It’s possible for them to be cancerous. Or a benign tumor can turn into cancer. But this is rare.

Types of nerve sheath tumors

The most common types are:

• Schwannomas: About 6 out of 10 (60%) affect the main nerve in your inner ear. Others form under your skin or deeper in your tissues and organs. They’re usually solitary (just one tumor). They’re almost always benign and slow-growing.
• Neurofibromas: These tumors usually appear as masses under your skin but can also affect deeper nerves. You may get one or many. Most are benign. But about 10 out of 100 (10%) become cancerous. Cancer transformation is more common in a subtype called plexiform neurofibroma.
• Malignant peripheral nerve sheath tumors: These cancerous tumors can arise on their own or if a neurofibroma turns malignant. They can form anywhere, but they usually show up on your arms and legs. They grow fast and can be challenging to treat.

Other types include:

• Granular cell tumor
• Hybrid nerve sheath tumor
• Nerve sheath myxoma
• Perineuroma
• Solitary circumscribed neuroma

Symptoms of nerve sheath tumors

Often, nerve sheath tumors don’t cause pain or other symptoms. But if the tumor gets big or presses on a nerve, it may cause:

• A lump under your skin (may feel tender if you press it)
• Muscle weakness
• Numbness
• Pins and needles, tingly feeling
• Pain (including the kind that radiates) that’s aching, burning or sharp
• Trouble coordinating your muscles

Nerve sheath tumors can cause specific symptoms if they press on a major nerve:

• Facial nerve: Trouble chewing, smiling or facial paralysis
• Sciatic nerve: Low back pain that radiates down your leg (sciatica)
• Vestibulocochlear nerve: Hearing loss, ringing in your ears and issues with balance

Nerve sheath tumor causes

Changes in your genes (mutations) cause nerve sheath tumors. Genes give your cells instructions on when to make more cells and when to die. But mutations lead to errors in the instructions. This can cause nerve sheath cells to make more cells when they shouldn’t. The extra cells form a mass, or tumor.

Most often, these changes happen at random. Doctors don’t know why.

But sometimes, people get nerve sheath tumors because they have a hereditary disease called neurofibromatosis (NF). Some forms may run in families. Still, about half of the people with NF don’t have a family history of the condition. The symptoms and lifetime cancer risk depend on the type of NF you have.

How to lower your risk

There’s nothing you can do to prevent nerve sheath tumors. But you may be able to learn your risk of passing the condition on to a child by getting genetic testing. The test checks for the common mutations (like NF1, NF2, SMARC-B, LZTR) in your genes.

Your healthcare provider may suggest testing if you have signs of neurofibromatosis. They include a personal or family history of nerve sheath tumors.

How doctors diagnose this condition

A healthcare provider will do a neurological exam and check your overall health. They’ll review your medical history, family history and symptoms.

Tests your healthcare provider may do include:

• Imaging, including an MRI, PET scans and an ultrasound to see the tumor inside your body
• Studies to check how your nerves are working, like nerve conduction studies and electromyography
• Hearing tests
• Biopsy to check for cancer cells in a sample of tumor tissue (if there are any concerning exam or imaging findings)
• Genetic testing to check for mutations

How are nerve sheath tumors treated?

Treatment requires a team of experts from neurosurgery, neuro-oncology, radiation oncology, plastic surgery, neurology, and orthopaedic oncology.

Your healthcare team may choose to wait on treatment if you have a benign tumor that isn’t causing symptoms. They’ll keep an eye on it and recommend treatment as needed.

If a tumor is causing symptoms, you may need surgery to remove it. Another option is stereotactic radiosurgery. This isn’t traditional surgery that involves cuts (incisions). Instead, it delivers a precise beam of radiation to destroy or shrink a tumor. You may need it if you have a tumor near nerves with essential functions that make surgery risky.

For tumors related to neurofibromatosis or schwannomatosis, there are U.S. Food and Drug (FDA)-approved targeted therapy options. These are medications that precisely attack tumor cells to stop their growth and shrink tumors.

Treatment for a cancerous nerve sheath tumor may include surgery, radiation therapy and chemotherapy.

When should I see my healthcare provider?

Your healthcare provider will monitor you closely after nerve sheath tumor treatment.

Surgery involving the nerves carries a possible risk of nerve damage and disability. Your healthcare team will work with you after surgery to manage any lasting disability challenges. Different types of therapy (physical, occupational and speech) may help you regain function.

What is the outlook for this condition?

Most nerve sheath tumors are noncancerous. They usually grow slowly and are treatable with surgery. They rarely come back. If your healthcare provider can’t remove the tumor completely, they’ll monitor you and help manage symptoms.

The risk of nerve sheath tumors becoming cancerous is low. The higher risk is for people with NF1 who develop plexiform neurofibroma, which can be 10% to 15% over a person’s lifetime.

Malignant peripheral nerve sheath tumors require surgical removal followed by radiation therapy and possibly chemotherapy. This depends on several factors, like tumor growth and cancer spread.

Still, your outlook depends on lots of things. They include the tumor stage, the type of mutation and your general health. These are factors your healthcare provider can discuss with you.

What is the survival rate for a nerve sheath tumor?

Benign nerve sheath tumors don’t usually affect life expectancy. The five-year survival rate for malignant peripheral nerve sheath tumors ranges from 23% to 69%. That means that anywhere from 23 to 69 people out of 100 are alive five years later. That’s a wide range, which is why it’s best to ask your provider about what these numbers mean for you.