Acoustic neuromas are benign tumors arising from the vestibular nerve in the base of the skull. These tumors grow slowly, expanding into the cranial cavity, compressing the brainstem and causing cranial nerve dysfunction. Affected individuals develop progressive hearing loss in one ear, ringing in the ear, a sense of imbalance, loss of sensation in the face and weakness of facial muscles. Very large tumors cause headaches, double vision and hydrocephalus. Interestingly, the surgical treatment of acoustic neuromas parallels the history of the development of neurosurgery.
Acoustic neuromas are rare. The incidence is 10 per million population per year or about 2,800 new cases in the US each year. These tumors are only rarely associated with genetic errors which are passed to succeeding generations. In Neurofibromatosis2 a genetic error is passed as an autosomal dominant trait ( one half of children maybe affected) and this error results in acoustic neuromas on both sides. Microsurgical removal and radiosurgery are effective methods of treating AN. Detailed information regarding the effects of treatment, the risks and complications, long term effects and natural history of untreated tumors form an important basis for every patient's informed decision regarding their own treatment. |
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| Several studies have detailed the growth pattern of untreated AN. About 50% of tumors grow slowly.. 1 to 2 millimeters per year. For each patient the growth rate is constant and can be predicted after 1 to 2 years of observation with serial MR scans. In about 20% the growth rate is more rapid: more than 2 mm per year. Finally tumors seem not grow in more than 30% of patients (some even become smaller). Malignancy is extremely rare. |
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The success of surgical removal of these tumors is a testament to the skills and resourcefulness of neurosurgeons and otologists. At the turn of the century, open operation was a risky proposition. The mortality rate was 80%. Now the operative mortality rate is 1% and the likelihood of surgical cure greater than 95%. In recent years surgeons have turned the emphasis from reduction of the mortality rate to reduction in complication rates and preservation of cranial nerve function. Now a days patients can expect to have near normal facial movement, sensation and sometimes even hearing preservation following microsurgical removal. A meta-analysis of the results of various microsurgical series is difficult as it is difficult to control for the many risk factors which influence the outcome of surgery. For example, the preservation of facial movement and hearing is highly influenced by tumor size. The following table summarizes several contemporary studies of microsurgery: The series of 1,000 patients personally operated by Professor Samii is a notable example of microsurgical results in the best of hands. He achieved total removal in 97.9% with a recurrence rate of 0.7% (without NF-2). Few patients had significant facial weakness before operation, while 27% had significant post op weakness. Most patients had reduced hearing prior and no hearing after operation. The mortality rate was 1.1%. Total complications were approximately 20% included cerebrospinal leak, meningitis, hemorrhage, hydrocephalus and about 4% with severe complications leading to permanent disability.
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