A nerve sheath tumor is a growth that forms in the protective covering surrounding a nerve. These tumors develop from Schwann cells, which produce the insulating layer (myelin) that wraps around nerve fibers. More than 90% of nerve sheath tumors are benign, but a small percentage are cancerous and require aggressive treatment.
The Two Most Common Types
Nerve sheath tumors fall into two main categories: schwannomas and neurofibromas. Together, these account for the vast majority of cases.
Schwannomas are the most common type. They’re made entirely of Schwann cells and typically grow slowly, forming a clear border that pushes nerve fibers to the side rather than growing through them. This distinction matters because it generally makes them easier to remove surgically without damaging the nerve. Schwannomas can develop on nerves throughout the body, including the arms, legs, face, and spinal nerve roots. One well-known subtype, the vestibular schwannoma, grows on the nerve connecting the brain to the inner ear and can affect hearing and balance.
Neurofibromas are slightly more common overall, accounting for roughly 60% of nerve sheath tumors in large studies, and contain a mix of cell types including Schwann cells, nerve fibers, and connective tissue. They come in three forms. Localized neurofibromas are the most frequent, usually appearing as painless bumps under the skin, typically smaller than 2 cm, with an extremely low risk of becoming cancerous. Diffuse neurofibromas tend to show up on the head or neck as broad, thickened patches of skin. Plexiform neurofibromas are the most concerning: they wrap around multiple nerve bundles, can grow large, and carry the highest risk of transforming into a malignant tumor.
What Nerve Sheath Tumors Feel Like
Many benign nerve sheath tumors grow slowly enough that they cause no symptoms at all and are discovered incidentally during imaging for something else. When symptoms do appear, they reflect the tumor pressing on or irritating the nerve it sits on.
Common symptoms include pain at the tumor site, tingling or “pins and needles” sensations, numbness, and weakness in the muscles supplied by that nerve. A schwannoma growing on a nerve in the arm or leg can mimic carpal tunnel or tarsal tunnel syndrome. Tumors on spinal nerve roots can produce symptoms that feel identical to a herniated disc: radiating pain, numbness, or weakness in a limb. Tumors affecting facial nerves may cause facial pain, difficulty swallowing, trouble moving an eye, or loss of taste.
When a Nerve Sheath Tumor Is Cancerous
Malignant peripheral nerve sheath tumors (MPNSTs) are rare, representing only about 2% of all nerve sheath tumors. Unlike their benign counterparts, they tend to cause symptoms that worsen quickly: escalating pain, a rapidly growing lump under the skin, and progressive weakness in the affected area.
Two groups face elevated risk. People with neurofibromatosis type 1 (NF1) have a significantly higher chance of developing MPNSTs, often arising from pre-existing plexiform neurofibromas. People who received radiation therapy for a previous cancer can also develop MPNSTs in the treated area, sometimes 10 to 20 years later.
The prognosis for MPNSTs depends heavily on whether the cancer has spread. For localized tumors, the five-year survival rate is around 55%. When metastasis is present at diagnosis, that drops to roughly 22%. Patients whose tumors arise in the context of NF1 tend to have somewhat worse outcomes than those with sporadic (non-inherited) tumors.
Genetic Conditions That Raise Risk
Most nerve sheath tumors occur sporadically, meaning they develop without an inherited cause. But three genetic syndromes dramatically increase the likelihood of developing them.
Neurofibromatosis type 1 (NF1) accounts for 96% of all neurofibromatosis cases. It’s caused by a mutation in a gene on chromosome 17 that normally keeps cell growth in check. People with NF1 develop multiple neurofibromas and face an elevated risk of those tumors becoming malignant.
Neurofibromatosis type 2 (NF2) involves a different gene on chromosome 22 and makes up about 3% of cases. It predisposes people to schwannomas, particularly vestibular schwannomas affecting hearing.
Schwannomatosis is the rarest form, caused by mutations in genes called SMARCB1 and LZTR1. These mutations are found in about 85% of familial cases and up to 40% of cases without a family history. People with schwannomatosis develop multiple schwannomas, often accompanied by significant chronic pain.
How Nerve Sheath Tumors Are Diagnosed
MRI is the primary imaging tool. Radiologists look for characteristic features that help distinguish benign tumors from malignant ones. Benign tumors tend to be smaller (under 5 cm), have a uniform appearance on imaging, and show no swelling in the surrounding tissue. Malignant tumors are more likely to be larger, irregular, and surrounded by edema or areas of tissue death. However, imaging alone isn’t always definitive, and a biopsy may be needed to confirm whether a tumor is cancerous.
Treatment and Recovery
Not every nerve sheath tumor needs to be removed. Small, incidentally discovered tumors that aren’t growing and aren’t causing symptoms can simply be monitored over time. Pain medications targeting nerve pain are often tried first for symptomatic tumors, though they rarely eliminate symptoms completely, and many patients eventually choose surgery.
For symptomatic benign tumors, the standard treatment is a technique called interfascicular resection. The surgeon carefully separates the tumor from the functional nerve fibers running along its surface. When done properly, about 90% of patients with a single, non-syndromic tumor experience symptom relief while preserving nerve function. Radiation and chemotherapy are not used for benign tumors.
Malignant tumors require a more aggressive approach: wider surgical removal, sometimes combined with radiation before or after surgery, and occasionally chemotherapy.
Recovery after nerve sheath tumor surgery varies. In cases where nerve tissue is preserved, most people regain useful function. When nerve reconstruction is necessary, roughly 77% of patients recover enough motor strength to use the affected limb functionally, and over 80% regain at least protective sensation. These outcomes are comparable to nerve repair after traumatic injuries. Nerve transfers, when used, tend to produce faster recovery and better strength outcomes because they reduce the time muscles spend without nerve input. Chronic pain after reconstruction is uncommon.