Schwannoma (Neurilemmoma) are benign tumours of the nerve sheath, which are cells and tissues covering the nerves. It is also known as schwannoma as the tumours arise from Schwann cells, which produce the myelin sheath that covers nerve fibres.
The peripheral nervous system is the network of nervous tissues outside the brain and spinal cord. Neurilemmomas may affect any location in the peripheral nervous system, for instance, the major nerve of the leg (the sciatic nerve), the nerves at the top of the arm (the brachial plexus), the lower back (the network of nerves called the sacral plexus) or any other network of nerves for a body part.
There is no known cause of schwannomas and these tumours are usually benign (not cancerous). The most common type of benign schwannoma is the acoustic neuroma, which affects the nerves that control hearing and may cause deafness. Only very few of the schwannomas become malignant and cancerous. The tumour cells grow very slowly with neurological symptoms (symptoms due to a nerve being affected) show up after many years. In some cases, a palpable mass that can be felt may be present.