Neurofibroma

by Bibianna Purgina MD FRCPC
June 7, 2023

What is a neurofibroma?

A neurofibroma is a common non-cancerous type of tumour that starts from the cells normally found in a nerve. It is the most common type of benign peripheral nerve sheath tumour.

What is a nerve?

Nerves are like long wires made up of groups of cells called neurons. Nerves transmit information (such as temperature, pressure, and pain) between your brain and your body. Nerves are found throughout your body. Some nerves are very small (like those just under the surface of the skin) while others are very large (like those that go to muscles).

What are the symptoms of a neurofibroma?

Most neurofibromas present as a painless, slow-growing lump just below the surface of the skin. Deeper tumours involving larger nerves may cause weakness or changes in sensation such as tingling, pain, or numbness.

What causes a neurofibroma?

At present, doctors do not know what causes a neurofibroma. However, it is well-established that people with the genetic syndrome neurofibromatosis type 1 (NF1) are at higher risk of developing multiple neurofibromas throughout their lifetime. Neurofibromas associated with NF1 are also more likely to change over time into a type of cancer called a malignant peripheral nerve sheath tumour (MPNST).

Where are neurofibromas found in the body?

Most neurofibromas arise from small nerves just below the surface of the skin. Less commonly, neurofibromas can arise from medium-sized nerves deeper within the body. Neurofibromas located close to the spinal cord are more common in people with NF1.

How do pathologists make this diagnosis? 

A pathologist may make a diagnosis of neurofibroma after a small sample of the tumour is removed in a procedure called a biopsy. Or a pathologist may make the diagnosis of neurofibroma if it is removed completely at first, without a biopsy.

What does a neurofibroma look like under the microscope?

Under the microscope, neurofibromas are made of spindle cells that look very similar to the cells in a normal nerve.  The tissue surrounding the tumour cells may be described as myxoid if it is light blue. The tumour cells may show mild cytologic atypia but mitotic figures (tumour cells dividing to create new tumour cells) are usually rare. If immunohistochemistry is performed, the tumour cells are typically positive for S100, SOX-10, and CD34.

Are there different types of neurofibromas?

Yes. Pathologists divide neurofibromas into different types depending on where in the body the tumour starts and how the tumour grows.

• Cutaneous neurofibroma – These tumours develop close to the skin.
• Intraneural neurofibroma – These tumours develop on the inside of a nerve.
• Diffuse neurofibroma – These tumours tend to grow a little deeper into the fat just below the skin.
• Plexiform neurofibroma – These tumours have an irregular shape and are often associated with NF1.