Acoustic neuroma also known as vestibular schwannoma is a rare benign (noncancerous) tumor that grows on the main nerve that extends from the inner ear to the brain. Branches from the main nerve influence balance and hearing thus pressure on the nerve from an acoustic neuroma may cause unsteadiness, loss of balance and hearing loss.
The tumor may grow slowly or not at all; however in rare cases it may develop rapidly causing large pressure and interference with vital functions.
The symptoms of an acoustic neuroma result from the tumor pressing onto the main nerve or adjacent nerves, blood vessels or brain structures.
Symptoms are more likely to occur as the tumor grows although it is possible for a small tumor to also cause serious signs and symptoms:
- Hearing loss (usually gradual but in some cases it may be sudden and more present on one side)
- Ringing in the affected ear
- Loss of balance
- Dizziness (vertigo)
- Facial numbness or weakness in rare cases
In some rare cases a large enough acoustic neuroma may compress the brainstem and become life threatening.
Early diagnosis of this condition will keep the tumor from growing and avoid serious consequences such as complete hearing loss or fluid buildup in the skull.
Acoustic neuromas are caused by a gene malfunction on chromosome 22. The purpose of the gene is to produce a protein that controls the growth of Schwann cells that cover the nerves. The reason for the gene malfunction is still undetermined; however, the faulty gene is inherited in neurofibromatosis type 2, which is a rare disorder involving tumor growths on balance nerves on both side of the head (bilateral vestibular schwannomas).
The only risk factor associated with acoustic neuromas is a parent with neurofibromatosis type 2 disorder, which is a genetic autosomal dominant condition meaning that the disorder can be passed on by the parent carrying the dominant gene. There is a 50-50 chance of a child inheriting this mutation from an affected parent.
An acoustic neuroma may cause a few permanent complications:
- Hearing loss
- Unsteadiness or loss of balance
- Ringing in the ear
- Facial numbness/weakness
Large acoustic neuromas may cause pressure on the brainstem obstructing the normal fluid flow between the brain and the spinal cord (cerebrospinal fluid). The obstruction of the normal flow of cerebrospinal fluid can cause a fluid build up in the head called hydrocephalus, which can increase the pressure in the skull to a dangerous level.