Stereotactic radiosurgery for acoustic tumors. 
Stereotactic radiosurgery is an important alternative treatment for carefully selected patients with acoustic tumors.  We perform radiosurgery under local anesthesia, and 91% of our patients have been discharged from the hospital within 24 hours after treatment.  All returned to their preoperative level of function or employment within 5 to 7 days after treatment.  Our current tumor control rate is 97%, but reduction in tumor size, judged by strict, objective criteria, was achieved in only 23%.  Our actuarial rate of useful hearing preservation after radiosurgery is 38% at 1 year.  Three tumors increased in size after treatment.  Only one of the three demonstrated increased mass effect on surrounding brain structures by neuroimaging criteria.  No increase has led to worsened clinical symptoms or has required surgical excision at this point in follow-up.  The 1-year rates for developing new facial or trigeminal neuropathies after radiosurgery were 30% and 33%, respectively.  Cranial neuropathies had a delayed onset, with the median onset occurring after 5 to 6 months.  The vast majority were partial at onset, and most improved over time.  Communicating hydrocephalus requiring ventriculoperitoneal shunts developed after radiosurgery in four patients.  Eight patients developed increased signal within adjacent brain parenchyma on T2-weighted MR imaging, consistent with edema or blood-brain barrier breakdown.  It is unlikely that stereotactic radiosurgery using the gamma knife will obviate the need for microsurgical removal performed by skilled and experienced microsurgeons.  However, radiosurgery is a safe and effective treatment for patients whose medical problems make surgery unacceptably dangerous, those with bilateral tumors or a tumor in their only hearing ear, those who have recurrent tumor despite surgical resection, or patients who refuse microsurgical excision.