Schwannomas

These relatively rare benign tumours are nonetheless the most common tumour of the peripheral nerves, and may affect any nerve in the body. They arise from the sheath surrounding the nerve (Schwann cells). In Schwannomas, cells are not organized like Schwann cells around the axons but instead in swirls and streaks across and among themselves. Schwannomas do not invade the nerve and can usually be surgically removed without damage to the adjacent nerve.
Schwannomas usually grow very slowly but they can become very large. Very large tumours can be seen or felt as a bulge under the skin.
Schwannomas (like neurofibromas) can occur singly or multiply. Multiple Schwannomas can occur on many different nerves or be limited to only one nerve or to one extremity.
Schwannomas (and neurofibromas) are seen in association with Neurofibromatosis (‘von Recklinghausen’s disease’). Schwannomas and neurofibromas look very similar on MR.
Although Schwannomas are benign (they do not metastasise), a small number (5-15% quoted in the literature) are more aggressive and some can even become malignant (malignant transformation) and very rarely metastasise. Watching with serial imaging and clinical examination is a reasonable approach but surgery may be best if there is any increase in size or more aggressive appearance. Schwannomas can often be removed with little injury to the nerve that they grow on, as opposed to neurofibromas whose removal usually requires division of the nerve around the tumour.