In contrast, those tumors associated with NF II are bilateral and account for approximately five percent (5%) of acoustic neuroma patients. Approximately ninety-five percent (95%) of all acoustic neuromas are sporadic cases and are unilateral. Many patients also exhibit no tumor growth over a number of years when followed by yearly MRI scans.Īcoustic neuromas occur in two forms: sporadic and those associated with Neurofibromatosis Type II (NF II). Usually, the symptoms are mild and many patients are not diagnosed until some time after their tumor has developed. In other cases, the growth rate is more rapid and patients develop symptoms at a faster pace. In the majority of cases, these tumors grow slowly over a period of years. As the tumors enlarge, they involve surrounding structures which have to do with vital functions. The location of these tumors is deep inside the skull, adjacent to vital brain centers in the brain stem. (Figure A) These tumors are non-malignant, meaning that they do not spread or metastasize to other parts of the body. The brain stem and its vital structures are adjacent to this region.Īcoustic neuromas are benign fibrous growths that arise from the balance nerve, also called the eighth cranial nerve or vestibulocochlear nerve. The vestibulocochlear (VIIIth cranial nerve) nerve travels in a bony canal, the internal auditory canal, with the facial nerve. Illustration of the anatomy of the temporal bone and inner ear structures. This translates to roughly three thousand (3,000) newly diagnosed acoustic neuromas per year in the United States based upon a population of around three hundred million. In the United States, approximately ten (10) people per million, per year are diagnosed with an acoustic neuroma. These tumors occur in all races of people and have a very slight predilection for women over men. Acoustic neuromas, also known as vestibular schwannomas, constitute approximately six percent (6%) of all brain tumors.
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