Benign peripheral nerve tumor


Nerves provide electrical messages from the brain to the rest of the body. They are made up of nerve cell bundles. These nerves govern the muscles, allowing people to move, blink, swallow, pick things up, and perform other tasks. Tumors may form on these peripheral nerves. Typically, the cause of these tumors is unknown. Some are caused by a genetic mutation.

Peripheral nerve tumors can cause nerve damage and loss of muscle control. Therefore, it is critical to have a proper diagnosis when there are any strange lumps, pain, tingling or numbness, or muscular weakness. In most cases, peripheral nerve tumors are benign or non-cancerous.

Peripheral nerve tumors are classified into two main categories: intraneural and extraneural. These tumors influence nerves by developing within or pressing against them. Intraneural tumors are peripheral nerve tumors that form within nerves. Extraneural tumors are tumors that press against nerves. The most common types of peripheral nerve tumors:

  • Schwannoma: These are made up of Schwann cells, the cells that surround the nerves. Schwannomas are encapsulated, which means they are confined and covered by a thin layer of tissue. These tumors are always benign and slow growing.

Schwannomas may develop practically anywhere on the body. The vestibular nerve in the inner ear is affected by around 60% of Schwannomas. Nerve sheath tumors are commonly found in the arms, legs, head, and torso. Schwannomas tend to develop alone. One could have a schwannoma for years before discovering it.

A schwannoma is often formed by a one bundle of nerve fibers within the main nerve, known as a fascicle. Some schwannomas, known as dumbbell tumors, grow and form unusual shapes within the spine or pelvis. As a schwannoma grows, the number of fascicles that may be endangered during a safe tumor removal procedure increases.

An acoustic neuroma, also known as vestibular schwannoma, is an uncommon schwannoma in the brainstem that affects the balance and hearing nerves. Acoustic neuromas can harm surrounding nerves and impinge on the brainstem if they are not treated and continue to grow. It can happen in patients who have a disorder called neurofibromatosis 2 (NF2).

  • Neurofibroma: These tumors affect numerous types of nerve sheath tissue, including Schwann cells, endoneurium, and perineurium. They usually form in the nerve’s center and may appear as nodules or lumps under the skin. However, they can also harm deeper nerves. Unlike schwannomas, they are not encapsulated or contained and can develop from multiple nerve bundles and cause minor symptoms.

The majority of neurofibromas are not malignant. Approximately 5% to 10% develop malignant peripheral nerve sheath tumors, which are cancerous tumors. People with neurofibromatosis type 1 (NF1) are more likely to develop a malignant peripheral nerve sheath tumor. NF1 is a hereditary condition that causes nerve tumors to form.

Color changes and benign tumors on the skin are symptoms of NF1. Some people with NF1 develop additional conditions including bone malformations, such as a bent spine, and optic glioma, a type of eye nerve tumor.

  • Perineurioma: This type of tumor can be classified into intraneural and extraneural perineuriomas. Intraneural perineurioma develops within a nerve, while extraneural develops in soft tissue near a nerve. Intraneural perineurioma is most common in children and young adults, which can lead to progressively increasing loss of feeling and weakness in an arm or leg. Perineuriomas are rare benign peripheral nerve sheath tumors that originate in the perineurial cell.
  • Lipoma: A lipoma rarely causes symptoms. However, it may require regular checkup and monitoring. A lipoma is a benign, soft lump caused by slow-growing fat cells. It can form under the skin on the neck, shoulders, back, or arms. A lipoma near a nerve can compress it.
  • Ganglion cyst: These are most common near the joints, such as the wrist, and can cause pain and interfere with daily activities. If the ganglion cysts press on nearby nerves, treatment may be necessary. In some cases, it resolves on its own. Ganglion cyst may be caused by an injury. However, in most cases, the cause is unknown.


Nerve sheath tumors frequently cause no pain or other symptoms. If the tumor expands in size or pushes on a nerve, it might cause symptoms. Symptoms vary depending on where the tumor is located and which tissues it affects. The tumor’s size may also increase the likelihood of symptoms. However, even small tumors might induce symptoms.

Common symptoms may include:

  • Swelling or a lump beneath the skin
  • Numbness
  • Muscle weakness
  • Aching, burning, or severe pain
  • A tingling sensation
  • Dizziness or a lack of balance


Some peripheral nerve tumors have an unknown cause. In some cases, it may be influenced by genetic alterations. The NF2 gene is linked to schwannomas, while the NF1 gene is linked to neurofibromas. These can be genetically handed down in families.

Most of the time, these genetic mutations are sporadic and occur at random. A small percentage of schwannomas and neurofibromas are caused by neurofibromatosis, a rare hereditary condition that runs in families. A schwannoma often begins in a single bundle within the main nerve, causing the rest of the nerve to move. A neurofibroma is a type of tumor that grows inside the nerve. It can grow from numerous nerve bundles at times. (1, 2)

Another benign peripheral nerve tumor is perineurioma. Although uncommon, it can develop from either inside or outside the nerve. When tumors outside a nerve impinge on it, they might cause issues. Other benign tumors that occur outside of nerves include ganglion cysts and lipomas, which are soft lumps of slow-growing fat cells.