Overview

Your peripheral nerves link your brain and spinal cord to other parts of your body. These nerves control your muscles so that you can walk, blink, swallow, pick things up and do other activities.

Several different types of tumors may form on the peripheral nerves. The cause of these tumors is usually unknown. Some have a genetic cause.

Most of these types of tumors are not cancerous (benign). But they can lead to nerve damage and loss of muscle control. That's why it's important to see your health care provider when you have any unusual lump, pain, tingling or numbness, or muscle weakness.

Types

Peripheral nerve tumors affect nerves by growing within them or by pressing against them. Peripheral nerve tumors that grow within nerves are called intraneural tumors. The tumors that press against nerves are called extraneural tumors. Most are benign, meaning that they are not cancerous. Different types of benign peripheral nerve tumors include:

  • Schwannoma. The most common benign peripheral nerve tumor in adults, a schwannoma can occur almost anywhere on the body. These nerve sheath tumors are called schwannomas because they are made up of Schwann cells, which are cells that surround the nerves.

    These tumors usually grow slowly. If you develop a schwannoma in an arm or leg, you might notice a mass. But you might have a schwannoma for years before noticing it.

    A schwannoma typically comes from a single bundle of nerve fibers, called a fascicle, within the main nerve. Some schwannomas grow and form unusual shapes within the spine or pelvis, such as dumbbell tumors. When a schwannoma grows, more fascicles are at risk when trying to remove the tumor safely.

    Schwannomas most commonly occur alone. Occasionally some people have several of them in the arms, legs or body. This is a condition called schwannomatosis.

    A rare schwannoma near the brainstem, known as an acoustic neuroma, can cause trouble with balance or hearing. This type of tumor also is known as a vestibular schwannoma. It sometimes occurs in people with a condition called neurofibromatosis 2 (NF2). If acoustic neuromas aren't treated and they continue to grow, they can affect nearby nerves and press on the brainstem.

  • Neurofibroma. This common type of benign nerve tumor tends to form in the center of a nerve. A neurofibroma might arise from several nerve bundles and tends to cause mild symptoms. This tumor most commonly develops in people who have neurofibromatosis 1 (NF1). This is a genetic disorder that causes tumors to grow on nerves.

    Symptoms of NF1 include color changes and benign tumors on the skin. Some people who have NF1 develop other conditions. These conditions include bone deformities, such as a curved spine, and an eye nerve tumor called an optic glioma. People with NF1 are at risk of developing a malignant peripheral nerve sheath tumor.

  • Perineurioma. This rare benign peripheral nerve tumor arises from perineurial cells, a type of cell that surrounds the peripheral nerve sheath. A perineurioma can form within a nerve, called an intraneural perineurioma. It may also form in soft next to a nerve, called an extraneural perineurioma. An intraneural perineurioma happens most often in children and young adults. It typically causes gradually progressive weakness and loss of feeling in an arm or leg.
  • Lipoma. Slow-growing fat cells cause this benign, soft lump that usually appears under the skin on the neck, shoulders, back or arms. A lipoma near a nerve can squeeze it. Usually, though, a lipoma causes no pain or other problems. Your health care provider might want to monitor a lipoma through regular checkups.
  • Ganglion cyst. Some ganglion cysts come from an injury, but most have no known cause. They commonly form near joints, such as the wrist, and can cause pain and interfere with everyday activities. Some go away without treatment, but ganglion cysts that press neighboring nerves should be removed.

Symptoms

A benign peripheral nerve tumor can cause symptoms if it presses on the nerve in which it is growing or on nearby nerves, blood vessels or tissues.

As the tumor grows, it may be more likely to cause symptoms, but even small tumors can sometimes cause symptoms. Symptoms depend on the location of the tumor and which tissues it affects. Symptoms may include:

  • Swelling or a lump under your skin
  • Pain, tingling or numbness
  • Weakness or loss of function in the affected area
  • Dizziness or loss of balance

Causes

The cause of benign peripheral nerve tumors usually isn't known. Some are passed down in families.

The most common type of benign peripheral nerve tumor is a schwannoma. A schwannoma typically starts in a single bundle inside the main nerve, shifting the rest of the nerve.

Another common type is a neurofibroma. A neurofibroma also often forms inside the nerve. Sometimes it grows from several nerve bundles.

Perineuriomas are rare and can grow from inside or outside the nerve. Tumors outside a nerve can cause problems when they press on the nerve. Other benign tumors that form outside nerves are soft lumps of slow-growing fat cells called lipomas and ganglion cysts.

By Mayo Clinic Staff