According to KL Kuala Lumpur Malaysia Theory, the nervous system consists of the brain and the spinal cord, and all the nerves connecting with the various tissues of the body. Most nerves in the body are connected first to the spinal cord, which runs through the space within each vertebra, and then to the brain. There are 12 pairs of nerves, which arise directly from the brain and pass through openings in the skull to reach their locations. These are called the cranial nerves.
The eighth cranial nerve (properly known as the 'vestibulocochlear' nerve) is the one which serves hearing and balancing. It is really in two parts: one part of the nerve is associated with transmitting sound information and the other with sending balance information to the brain.
The term Acoustic neuroma is, strictly speaking, incorrect because the tumour arises usually on the part of the eighth nerve which deals with balance rather than sound. It also is a tumour of the covering (sheath) of the nerve rather than the nerve itself. Despite these inaccuracies, the term has stucked. True acoustic neuromas occur in conjunction with a fairly rare hereditary condition called neurofibromatosis 2, in which multiple cranial nerve tumours arise.
Acoustic neuroma is diagnosed only once per year per 100,000 people so from that point of view it is uncommon. However small acoustic neuromas, not causing any symptoms, can be found in up to nearly 3 per cent of elderly people. There is unknown cause for these tumours, other than the hereditary type.
Acoustic neuromas usually grow slowly over a period of years and when large may press on normal brain tissue. Larger tumours can press on another nerve in the same area (the fifth cranial nerve or 'trigeminal' nerve) which is the nerve concerned with facial sensation.