What are nerve sheath tumors?
Nerves transmit electrical signals between your brain and your body. They’re made up of bundles of nerve cells. The cells, bundles and nerves are all wrapped in layers of protective tissues that provide insulation and help the electrical signals move faster.
Nerve sheath tumors form in these layers of insulation. These layers include:
- Schwann cells: Cells that wrap around the long area of the nerve cell called the axon, or fiber.
- Endoneurium: Connective tissue that surrounds each nerve fiber, like the coating around a wire.
- Perineurium: Connective tissue that surrounds bundles of nerve fibers.
Your nervous system is made up of your:
- Central nervous system: Your brain and spinal cord.
- Peripheral nervous system: A network of nerves that branch off to the rest of your body.
Nerve sheath tumors usually affect your peripheral nervous system.
What are the types of nerve sheath tumors?
The most common types of nerve sheath tumors are:
These occur in Schwann cells. About 60% of Schwannomas affect the vestibular nerve in your inner ear. Others form under your skin or deeper in your tissues and organs. Common locations of nerve sheath tumors include:
- Arms and legs.
- Torso (between your shoulders and hips).
Schwannomas are encapsulated — meaning, contained; covered with a thin layer of tissue — and are almost always noncancerous (benign). Very rarely, long-lasting tumors can become cancerous (malignant).
These tumors involve several types of tissue in the nerve sheath, including Schwann cells, endoneurium and perineurium. They usually appear under your skin as nodules or masses, but can also affect deeper nerves.
Neurofibromas aren’t encapsulated, or contained, like schwannomas, and penetrate between bundles of nerves. Plexiform neurofibromas are web-like and surround multiple nerve bundles. They can extend into nearby tissues.
Most neurofibromas are noncancerous. Approximately 5% to 10% become cancerous tumors called malignant peripheral nerve sheath tumors. In about half of people with malignant tumors, cancer has spread to other parts of their body at the time of diagnosis.
How common are nerve sheath tumors?
Benign nerve sheath tumors are relatively rare. Schwannomas are most common in people between the ages of 50 and 60. Neurofibromas most often occur in people between the ages of 20 and 40. Plexiform neurofibromas usually develop before age 5.
Malignant peripheral nerve sheath tumors are extremely rare, affecting about 1 out of every 10 million people each year.
Symptoms and Causes
What causes nerve sheath tumors?
Genetic changes play an important role in the development of nerve sheath tumors. Alteration of the NF2 gene is linked to schwannomas, while the NF1 gene is associated with neurofibromas.
Most often, these genetic changes are sporadic and happen randomly. A small fraction of schwannomas and neurofibromas are caused by a rare, genetic disease that runs in families called neurofibromatosis.
The types of neurofibromatosis are:
- Neurofibromatosis type 1 (NF1): People with NF1 have multiple neurofibromas. They might also develop plexiform neuromas and are at higher risk of malignant peripheral nerve sheath tumors. Other conditions common in people with NF1 include large head (macrocephaly), curvature of their spine (scoliosis) and learning disabilities.
- Neurofibromatosis type 2 (NF2): Nearly all people with NF2 develop vestibular schwannomas in both ears before age 30. Other schwannomas and types of tumors can also appear on their skin, in their eyes and in their central nervous systems.
- Schwannomatosis: This condition causes multiple schwannomas but without vestibular nerve tumors in both ears.
What are the symptoms of nerve sheath tumors?
People with nerve sheath tumors often have no pain or other symptoms. If the tumor grows large or presses on the nerve, it may cause:
- Lump or mass under their skin that may be painful when pressed.
- Muscle weakness.
- Pain that’s aching, burning or sharp.
- Tingling feeling.
Nerve sheath tumors can cause other symptoms depending on their location. Some specific symptoms for different tumor locations include:
- Sciatic nerve: Lower back pain that radiates down their leg (sciatica).
- Wrist: Symptoms similar to carpal tunnel syndrome.
- Vestibular nerve: Decreased hearing, ringing in ears (tinnitus) and difficulty with balance.
In general, people with nerve sheath tumors will have a single tumor. In neurofibromatosis, multiple tumors (usually on their skin) are common.
Diagnosis and Tests
How are nerve sheath tumors diagnosed?
Your healthcare provider will perform a physical exam and an assessment of your overall health. This includes a review of your medical history, family history and symptoms.
Tests your healthcare provider may recommend to evaluate an observed or suspected tumor include:
- Medical imaging, including MRI, ultrasound and PET scans to see the tumor.
- Removal of a sample of tissue for microscopic examination (biopsy) to find out what kinds of cells are in the tumor. This’ll determine if the tumor is cancerous.
If you have multiple tumors, your healthcare provider will recommend genetic testing to evaluate you for NF1, NF2 and schwannomatosis.
Management and Treatment
How are nerve sheath tumors treated?
If a nerve sheath tumor isn’t causing symptoms, your healthcare provider may choose to watch and wait. Routine monitoring will reveal if the tumor is growing or changing.
For symptomatic tumors, or if you want the tumor removed for cosmetic reasons, surgery is usually the only option.
Some neurofibromas, especially plexiform neurofibromas, are difficult to remove because they grow into the nerve and between the layers of insulation. If surgery results in incomplete removal, your healthcare provider will monitor you closely, as the tumor may come back.
How are schwannomas in the head treated?
Schwannomas in your head, such as vestibular schwannomas, may involve nerves that control critical functions. In these areas, healthcare providers use stereotactic radiosurgery (Gamma Knife®) to prevent nerve damage.
This isn’t traditional surgery that involves an incision. Instead, it uses a precise beam of radiation delivered through your skin to destroy or shrink the tumor.
How are malignant peripheral nerve sheath tumors treated?
What are possible complications of nerve sheath tumor surgery?
General complications of surgery include:
- Local infection.
Surgery involving the nerves also carries a risk of nerve damage and permanent 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.
Can I prevent nerve sheath tumors?
There isn’t a known way to prevent these types of tumors. Your healthcare provider may recommend genetic testing to better understand you and your family’s risk if you:
- Have a family history of nerve sheath tumors.
- Develop multiple nerve sheath tumors, which may be a sign of neurofibromatosis.
Outlook / Prognosis
What is the outlook for nerve sheath tumors?
Most nerve sheath tumors are noncancerous. They’re treatable with surgery and rarely come back. If your tumor can’t be completely removed surgically, you’ll require ongoing monitoring.
About 3 in 4 patients treated for vestibular schwannoma will retain their ability to hear.
The risk of nerve sheath tumors becoming cancerous is very low. The greatest risk is for people with NF1 who develop plexiform neurofibroma. Malignant peripheral nerve sheath tumors have a poor prognosis, especially if the tumor is larger than 2 inches. Fewer than half of people with this condition live five years after diagnosis.
When should I see my healthcare provider?
Call your healthcare provider if you notice any lumps under your skin or if you experience symptoms that might indicate a nerve sheath tumor. You should also let your healthcare provider know if these types of tumors run in your family.
A note from Cleveland Clinic
Nerve sheath tumors are usually noncancerous. They grow slowly, and your healthcare provider may opt for observation if you're not having any symptoms. When a tumor requires removal, surgery is usually highly effective. Rarely, surgical complications such as incomplete removal of the tumor or damage to the nerve can occur. Very rarely, a tumor can turn into cancer. Your healthcare provider will work with you to develop a plan for treatment and follow-up care to successfully manage your condition.
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