Vestibular schwannoma
A vestibular schwannoma (VS), also called acoustic neuroma, is a benign tumor that develops on the vestibulocochlear nerve that passes from the inner ear to the brain. The tumor originates when Schwann cells that form the insulating myelin sheath on the nerve malfunction. Normally, Schwann cells function beneficially to protect the nerves which transmit balance and sound information to the brain. However, sometimes a mutation in the tumor suppressor gene, NF2, located on chromosome 22, results in abnormal production of the cell protein named Merlin, and Schwann cells multiply to form a tumor. The tumor originates mostly on the vestibular division of the nerve rather than the cochlear division, but hearing as well as balance will be affected as the tumor enlarges.
| Vestibular schwannoma | |
|---|---|
| Other names | Acoustic neuroma, acoustic neurilemmoma, perineural fibroblastoma, neurinoma of the acoustic nerve, neurofibroma of the acoustic nerve, schwannoma of the acoustic nerve |
| Bilateral schwannomas in a patient with neurofibromatosis 2 | |
| Specialty | Neuro-oncology |
| Symptoms | Gradual hearing loss, dizziness, tinnitus |
| Complications | Brain tumor growth; unilateral facial paralysis, single-sided hearing loss |
| Types | Sporadic vestibular schwannoma (VS); Neurofibromatosis type II (NF2) |
| Diagnostic method | Hearing exam, MRI exam |
| Prevention | Tumor management |
| Treatment | Radiosurgery and radiotherapy |
| Prognosis | Variable, based on size of tumor; larger brain tumors may result in brainstem compression, headache, vomiting, vertigo, fatigue, mental disorientation, coma, and death; results in less acute circumstances by advanced specialists in the field have reduced mortality rates to near 1% |
| Frequency | Very rare |
The great majority of these VSs (95%) are unilateral, in one ear only. They are called "sporadic" (i.e., by-chance, non-hereditary). Although non-cancerous, they can do harm or even become life-threatening if they grow to press on other cranial nerves and vital structures such as the brainstem. Variations in the mutation determine the nature of the tumor's development. The only environmental exposure that has been definitely associated with the growth of a VS is therapeutic radiation exposure to the head.