Vestibular schwannoma is also known as acoustic neuroma. It is a benign tumor, which grows from the eighth cranial nerve. Its occurrence is relatively rare and it is estimated in about 1 man in 100,000 a year. First, it is necessary to say some basic information about the eighth cranial nerve, its anatomy and function.
The eighth cranial nerve is paired, it runs from the area of inner ear and it consists of two main components – auditory (cochlear) and statokinetic (vestibular) part. Their fibers run together, but they transfer different kind of information. Auditory nerve fibers bring information about sounds from the cochlea and vestibular nerves inform us about stability, balance and the position of our body in three-dimensional space. Both types of nerve fibers join and enter the brain a single nerve.
Vestibular schwannoma arises from peripheral covering layers of vestibular nerve fibers. The cause of the tumor occurrence is not known, but the risk factors include higher age and genetic predisposition. Vestibular schwannoma may occur on one or both sides, its bilateral occurrence is typical for a certain subtype of neurofibromatosis.
Vestibular schwannoma has variable speeds of growth from virtually non-growing to very fast growing aggressive tumors. Initially, it has no symptoms. Later, the symptoms depend of mechanical compression and damage of nearby anatomical structures. The patients suffer from auditory disorders including hearing loss and tinnitus (ringing, buzzing and hissing noises in the ear on the affected side). Damage of vestibular nerve causes balance disorders, dizziness, nausea and vomiting. Large tumors may even damage the fifth and seventh cranial nerves that are located anatomically close. These nerves provide sensitivity of the face (the fifth nerve) and mobility of mimic facial muscles (the seventh nerve). Therefore, their damage may cause unilateral (or bilateral) disorder of facial sensitivity and muscle paralysis. Advanced forms of large tumors may even increase the intracranial pressure and this situation can be fatal.
A patient with the above mentioned problems is usually examined by a neurologist and otolaryngologist. Auditory nerve can be examined by audiometric examination and the anatomical area of inner ear and the eight cranial nerve may be well-visualized by computed tomography or magnetic resonance imaging.
The tumor must be removed and the smaller it is, the better results the therapy has. Larger tumors are removed by neurosurgeons, who try to preserve the function of inner ear. Smaller acoustic neuromas may be destroyed by local irradiation using the Leksell gamma knife. The asymptomatic elderly people, where a neurosurgical operation is too risky, slowly growing schwannomas may be only carefully monitored.