by Bibianna Purgina, MD FRCPC
October 1, 2022
Schwannoma is a non-cancerous type of nerve tumour and the most common type of nerve tumour in adults. The tumour is made up of specialized nerve cells called Schwann cells. This tumour can occur at any age and in any location in the body. Schwannomas that develop inside the ears are called acoustic neuromas. Other names for this tumour include neurilemoma and neurinoma.
Most schwannomas are sporadic, meaning doctors do not know why they occur. However, people with the genetic syndrome neurofibromatosis type 2 (NF-2) are more likely to develop multiple tumours as a result of the loss of the normal activity of the gene NF2.
Because they are slow-growing, most schwannomas do not result in any symptoms until the tumour becomes large enough to put pressure on surrounding organs and tissues. However, some patients with this type of tumour experience mild symptoms such as pain or tingling in the area of the tumour.
Schwannomas are non-cancerous tumours. However, a very small number of tumours (less than 5%) will turn into a type of cancer called malignant peripheral nerve sheath tumour (MPNST) over time. Tumours that turn into cancer are usually very large and have been present for many years.
A pathologist may make a diagnosis of schwannoma after a small sample of the tumour is removed in a procedure called a biopsy. The diagnosis can also be made after the tumour is removed completely without a biopsy.
Under the microscope, schwannomas are made of spindle cells that look very similar to the Schwann cells that make up a normal nerve. When pathologists perform a test called immunohistochemistry, the tumours stain strongly for the markers S100 and SOX-10.
Most schwannomas are called “conventional” because they show very typical microscopic features. Schwannomas that show less common microscopic features are called histologic subtypes and each subtype is given a special name. Histologic subtypes include ancient schwannoma, cellular schwannoma, melanotic schwannoma, epithelioid schwannoma, and plexiform schwannoma.