Cranial Nerve Preservation After Stereotactic Radiosurgery for Small Acoustic Tumors

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Abstract
Objective: To assess those factors associated with and predictive of cranial nerve preservation after stereotactic radiosurgery in patients with small acoustic tumors identified by magnetic resonance imaging. Design: We performed a retrospective analysis of our experience with 31 patients with preserved hearing and acoustic tumors measuring 10 mm or smaller (pons-to-petrous dimension). All patients underwent clinical and audiologic evaluations varying from 6 to 48 months (mean, 20 months) after stereotactic radiosurgery performed with use of the 201 source cobalt 60 gamma unit. Results: Stabilization or reduction in tumor volume was achieved in 29 of 31 patients. One patient required delayed microsurgical resection. Useful hearing (pure tone average ≤50 dB and speech discrimination score ≥50%) preservation was achieved in 10 of 10 patients immediately postoperatively, eight of 10 patients at 6 months, six of 10 patients at 1 year, and five of 10 at 2 years. Preservation of some measurable hearing was possible in all patients immediately after radiosurgery, in 84% and in more than half of patients at 2 years. Preoperative facial nerve function was preserved in 19 of 20 patients at 2 years after radiosurgery. All patients returned to their preoperative employment status within 2 to 5 days after radiosurgery. Conclusion: Stereotactic radiosurgery performed with current technology (multiple radiation isocenters and magnetic resonance imaging guidance) is a safe and effective management strategy for patients with small acoustic tumors. The risk of facial and trigeminal neuropathy after gamma knife radiosurgery is low, and useful hearing can be preserved in up to 50% of patients with useful preoperative hearing. Stereotactic radiosurgery is a valuable alternative strategy to surgical removal for many patients with newly diagnosed small acoustic tumors.

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