Your pathology report for schwannoma

by Bibianna Purgina, MD FRCPC
December 17, 2025

Schwannoma is a benign (non-cancerous) tumour that develops from Schwann cells, specialized cells that normally wrap around and protect nerves. Schwannoma is part of a larger group of tumours called peripheral nerve sheath tumours, which arise from the cells that support and surround nerves. In a schwannoma, Schwann cells grow slowly and form a mass along a nerve or next to it. These tumours are usually well defined and grow separately from the nerve fibres themselves.

Most schwannomas are solitary and occur sporadically. Less commonly, multiple schwannomas can be seen in people with inherited conditions such as neurofibromatosis type 2 or schwannomatosis.

Where is a schwannoma found?

Schwannomas most often arise from peripheral nerves in the skin or the tissue just beneath the skin. Common locations include the head and neck, arms, and legs, especially along flexor surfaces.

They are also commonly found along spinal nerves, where they may grow inside the spinal canal. When these tumours extend through openings in the spine, they can form a “dumbbell” shape. Schwannomas involving cranial nerves are also well recognized, especially tumours arising from the vestibular portion of the eighth cranial nerve. These are often called vestibular schwannomas and may affect hearing and balance.

Schwannomas arising within the spinal cord, brain tissue, internal organs, or bone are uncommon.

What are the symptoms of schwannoma?

Schwannomas grow slowly and many cause no symptoms. They are often discovered incidentally on imaging studies done for other reasons or as a painless lump under the skin.

When symptoms occur, they usually depend on the location of the tumour. Schwannomas involving peripheral nerves may cause localized pain, tenderness, tingling, or numbness. In people with schwannomatosis, pain can be a prominent feature even when tumours are small.

Spinal schwannomas can cause nerve-related pain that radiates along the nerve’s path, as well as weakness or sensory changes if the tumour presses on the spinal cord or nerve roots. Vestibular schwannomas often present with hearing loss, ringing in the ears, dizziness, or balance problems.

What causes a schwannoma?

In most cases, schwannomas are sporadic, which means they occur by chance and are not inherited or passed down through families. In these sporadic cases, the exact cause is not known.

Many schwannomas are associated with loss of function of the NF2 gene, which encodes the protein merlin. Merlin usually helps control cell growth. When it is lost, Schwann cells can grow uncontrolled. Changes affecting the NF2 gene are found in many sporadic schwannomas.

Some schwannomas occur as part of inherited conditions. Neurofibromatosis type 2 is characterized by multiple schwannomas, often involving both vestibular nerves. Schwannomatosis is another condition associated with multiple schwannomas, usually without vestibular nerve involvement. These conditions involve inherited gene mutations, such as those in NF2, SMARCB1, or LZTR1.

How is the diagnosis made?

The diagnosis of schwannoma is usually made by examining a tissue sample under the microscope. This may be obtained by biopsy or surgical removal of the tumour.

Under the microscope, schwannomas are composed almost entirely of Schwann cells that have a spindle cell shape. Spindle cells are long, narrow cells that taper at both ends, resembling a stretched oval or spindle. This shape is typical of cells that form supportive tissues, such as nerves.

Most schwannomas show a mixture of two growth patterns. One pattern is more compact and cellular, while the other is looser and less dense. In some areas, the spindle-shaped Schwann cells align in an orderly manner, forming characteristic structures called Verocay bodies. These features help pathologists recognize a schwannoma.

Immunohistochemistry, which uses special stains to highlight proteins in the tumour cells, strongly supports the diagnosis. Schwannomas show strong, diffuse staining for proteins such as S100 and SOX10, which are characteristic of Schwann cells. Other stains may be used to help exclude similar-appearing tumours.

Molecular testing is not usually required to diagnose schwannoma. Although NF2 gene changes are common, they are not specific enough to be diagnostic on their own.

Subtypes of Schwannoma

Several subtypes of schwannoma are recognized. All are benign, but some have features that can mimic more aggressive tumours and therefore are important to recognize.

Ancient schwannoma

This subtype shows degenerative changes, including large, atypical-appearing nuclei. These changes can look concerning under the microscope, but they are not a sign of cancer. Areas of scarring or reduced blood supply may also be present.

Cellular schwannoma

Cellular schwannoma is made up almost entirely of densely packed spindle-shaped Schwann cells and lacks the looser areas seen in conventional schwannoma. These tumours often occur near the spine or deep within the body. Despite increased cellularity and mitotic activity, supportive features such as a capsule and characteristic blood vessels help confirm the benign nature of the tumour.

Plexiform schwannoma

This subtype grows in a multinodular or branching pattern, often involving the skin or superficial soft tissues. It is more likely to appear in childhood. A well-formed capsule may be absent, and multiple nodules may be present.

Epithelioid schwannoma

In this subtype, tumour cells are rounder and resemble epithelial cells rather than typical spindle-shaped Schwann cells. The cells often grow in nests within a loose background. Rare cases show progression to a malignant tumour.

Microcystic or reticular schwannoma

This rare subtype most often occurs in internal organs, especially the gastrointestinal tract. The tumour shows a network of small spaces surrounded by bland spindle cells. Classic features such as Verocay bodies are usually absent, but strong S100 staining supports the diagnosis.

What is the prognosis for a person with a schwannoma?

Schwannomas are benign tumours and have an excellent prognosis. When completely removed, they do not usually recur. Some subtypes, such as cellular or plexiform schwannoma, can be more difficult to remove completely because of their location or growth pattern.

Malignant transformation means that a benign tumour changes over time into a cancerous tumour. Malignant transformation of a conventional schwannoma is exceptionally rare. When it occurs, it most often results in a malignant peripheral nerve sheath tumour.

Questions to ask your doctor

• Was the tumour completely removed?
• Is there a chance it could come back?
• Do I need follow-up imaging or exams?
• Should I be evaluated for a genetic condition such as neurofibromatosis or schwannomatosis?