Schwannoma: Understanding Your Pathology Report

Section Editor: Bibianna Purgina MD FRCPC
September 24, 2026

A schwannoma is a noncancerous tumor that develops from Schwann cells, which wrap around and protect nerves. It belongs to a group of tumors called peripheral nerve sheath tumors, and it is the most common tumor of this type.

A schwannoma grows slowly and forms a rounded mass attached to a nerve. It usually pushes the nerve fibers aside rather than growing through them, so a surgeon can often remove it while sparing the nerve. Schwannomas do not spread to other parts of the body.

Most schwannomas occur on their own, in people with no related condition. Less often, a person develops several schwannomas as part of an inherited condition.

This article explains how a schwannoma is diagnosed and what the subtype, immunohistochemistry results, and other findings in your pathology report mean.

Where does a schwannoma develop?

Schwannomas most often arise from nerves in the skin or in the tissue just beneath it. Common locations include the head and neck, the arms, and the legs, particularly on the inner surfaces of the limbs.

They also occur along the nerves of the spine, where a tumor may grow inside the spinal canal and extend out through an opening in the bone. This produces a shape that reports sometimes describe as a dumbbell.

Schwannomas of the cranial nerves are well recognized. The most common type arises from the nerve that carries hearing and balance signals and is called a vestibular schwannoma. Schwannomas that develop inside the brain, spinal cord, internal organs, or bone are uncommon.

What are the symptoms of a schwannoma?

Many schwannomas cause no symptoms and are found by chance on imaging done for another reason, or noticed as a painless lump under the skin.

When symptoms do occur, they depend on the location of the tumor:

Nerves in the arms, legs, or skin. Local pain, tenderness, tingling, or numbness. Tapping over the lump may send a brief electric sensation along the nerve.
Nerves of the spine. Pain that travels along the nerve, along with weakness or changes in sensation if the tumor presses on the spinal cord or a nerve root.
The hearing and balance nerve. Hearing loss on one side, ringing in the ear, dizziness, or problems with balance.

What causes a schwannoma?

Most schwannomas occur by chance and are not inherited. In these tumors, the Schwann cells lose the function of a gene called NF2, which makes a protein called merlin. Merlin normally helps control cell growth, and when it stops working, the cells grow into a tumor. This change happens in the tumor cells during a person’s lifetime.

A minority of people develop several schwannomas as part of an inherited condition. The names of these conditions were revised by an international group in 2022, so you may see both the old and new terms:

NF2-related schwannomatosis. This condition was previously called neurofibromatosis type 2. The name changed because people with it develop schwannomas rather than neurofibromas. It typically causes schwannomas on the hearing and balance nerve on both sides.
Schwannomatosis caused by other genes. These conditions are now named for the gene involved, such as SMARCB1-related schwannomatosis or LZTR1-related schwannomatosis. They cause multiple schwannomas, usually without tumors on both hearing nerves, and pain is often a prominent symptom.

Having a single schwannoma is not a reason to suspect an inherited condition. Genetic assessment is usually considered when a person has several schwannomas, a tumor at a young age, or a family history.

How is the diagnosis made?

The diagnosis of a schwannoma is made after a pathologist examines tumor tissue under the microscope. The tissue may come from a biopsy or from surgery that removes the whole tumor.

Under the microscope, a schwannoma is made almost entirely of spindle cells, which are long, narrow cells that taper at each end. Most schwannomas contain two patterns side by side. One area is compact and cellular, and pathologists call it Antoni A. The other is looser and less dense, and is called Antoni B. In the compact areas, the cells may line up in rows around a pink center, forming structures called Verocay bodies.

A capsule usually surrounds a schwannoma and contains thick-walled blood vessels. Together, these features and the two patterns allow a pathologist to recognize the tumor.

Immunohistochemistry

Immunohistochemistry is a test that uses antibodies to show which proteins cells make. For a schwannoma, the results strongly support the diagnosis.

S100 and SOX10. Schwann cells make these proteins. In a schwannoma, staining is strong and involves nearly all of the tumor cells.
Other stains. Additional stains may be used to rule out similar-looking tumors, including melanoma and other spindle cell tumors.

The strong, widespread staining pattern is often sufficient. In a malignant peripheral nerve sheath tumor, S100 and SOX10 are usually positive in only scattered cells or are negative.

Molecular testing is not usually needed. NF2 changes are common in schwannomas but are not specific enough to make the diagnosis on their own.

Subtypes of schwannoma

Your report may describe a specific subtype. All of these are noncancerous, and some are worth recognizing because they can look concerning under the microscope:

Ancient schwannoma. This subtype shows changes that develop in a tumor that has been present for a long time. These include large, odd-looking nuclei, scarring, and areas with reduced blood supply. These changes can look worrisome but do not indicate cancer.
Cellular schwannoma. This subtype is made almost entirely of densely packed cells, without the looser areas. It often occurs near the spine or deep in the body. Despite the crowding and increased cell division, the capsule and blood vessel pattern confirm it is noncancerous. This subtype is sometimes mistaken for a cancer.
Plexiform schwannoma. This subtype grows as multiple connected nodules, often in the skin or the tissue just beneath it. It is more common in childhood and may lack a well-formed capsule.
Epithelioid schwannoma. In this subtype, the cells are rounder and resemble epithelial cells, and they grow in nests. Rare cases have been reported to change into a cancerous tumor.
Microcystic or reticular schwannoma. This rare subtype usually develops in internal organs, especially the digestive tract. It forms a network of small spaces, and Verocay bodies are usually absent.

How is a schwannoma different from a neurofibroma?

Both are noncancerous nerve sheath tumors, and both can appear as a lump along a nerve. A neurofibroma contains a mixture of cell types and grows among the nerve fibers, which can make it harder to separate from the nerve at surgery.

A schwannoma is made of Schwann cells alone, has a capsule, and pushes the nerve aside. Under the microscope, S100 and SOX10 stain nearly all the cells of a schwannoma, while staining is patchier in a neurofibroma.

Margins

A margin is the edge of tissue cut by the surgeon. Your report may note whether tumor reaches the cut edge.

For a schwannoma, a positive margin does not carry the meaning it does for cancer. Surgeons sometimes leave a small amount of tumor behind on purpose to protect the nerve, which can prevent numbness or weakness. When this happens, doctors usually monitor the remaining tumor rather than treat it.

What is the prognosis?

The outlook is excellent. A schwannoma is noncancerous and does not spread. Once completely removed, it usually does not come back.

Some subtypes are harder to remove completely because of their location or growth pattern, particularly cellular and plexiform schwannomas, and these come back more often. A tumor that comes back is still noncancerous.

Change into a cancerous tumor is exceptionally rare. When it does happen, the result is usually a malignant peripheral nerve sheath tumor. This is rare enough that it is not a reason for concern with a typical schwannoma.

What happens after the diagnosis?

Treatment depends on the size and location of the tumor and on the symptoms it causes.

Observation. A small schwannoma that causes no symptoms may be monitored with exams and imaging.
Surgery. Removal is the usual treatment when a tumor causes symptoms or is growing. The surgeon works to remove the tumor while preserving the nerve, although some numbness or weakness can occur afterward.
Treatment for vestibular schwannoma. Options include observation, surgery, and focused radiation. The choice depends on the size of the tumor, your hearing, and your symptoms.
Follow-up. Imaging may be repeated if part of the tumor was left behind or if you have an inherited condition associated with multiple schwannomas.

Questions to ask your doctor

Was the whole tumor removed?
Which schwannoma subtype does my report describe?
Was any tumor left behind to protect the nerve?
Is there a chance this tumor could come back?
Should I expect any lasting numbness or weakness?
Do I need follow-up imaging, and for how long?
Should I be assessed for an inherited condition such as schwannomatosis?