A schwannoma, also called neurilemmoma, is a benign, slow-growing mass or tumor arising from the schwann cells. Schwann cells are components of myelin sheaths, which cover the axons or branches of nerve cells. They are involved in the proper functioning of nerve cells, in their development and regeneration, and in the conduction of nerve impulses throughout the body. The cause of schwannoma is still unknown, although certain factors, such as genetic predisposition, can increase the risk for the development of the tumor. For instance, individuals who have a family history of neurofibromatosis or von Recklinghausen disease have a higher risk for developing this condition.
Cranial nerves in the brain are often affected by schwannoma. Among the 12 cranial nerves, the most commonly affected include the vestibular nerves, which are found in the ears for hearing sensation; the trigeminal nerve, which is involved in facial sensation and motor functions such as chewing and swallowing; and the glossopharyngeal nerve, which supplys taste sensation to the tongue. When a schwannoma develops in one of the cranial nerves, loss of function usually follows, although sometimes the tumor can present with no symptoms and is seen incidentally only during a computed tomography (CT) scan or magnetic resonance imaging (MRI) done for other medical reasons.
Several symptoms are generally experienced by patients with cranial nerve schwannomas, often depending on the nerve involved. As the tumor enlarges, it may compress the nerve and other adjacent structures in the brain. In a vestibular schwannoma or acoustic neuroma, the patient may experience ringing in the ears, numbness of the face, gradual loss of hearing, and loss of balance. A glossopharyngeal schwannoma may manifest with hoarseness and swallowing difficulty. Trigeminal schwannomas may present with facial pain and double vision.
Aside from the cranial nerves, a schwannoma may also develop in the nerves of the legs, arms, and lower back. Pain is sometimes felt as the tumor gradually grows in size. Tinel shock, described as an electric-like shock, may also be felt when the affected area is touched.
A biopsy is usually needed to diagnose the tumor and to rule out a malignant schwannoma. Treatment includes the removal of the tumor by surgically separating it from the nerve, ideally without causing damage to the nerve's function. Radiotherapy and chemotherapy are also incorporated to shrink the tumor or hinder its further growth. The tumors, however, can recur in the same place after surgical removal if they are not completely removed.