The Laryngoscope Lippincott Williams & Wilkins © 2008 The American Laryngological, Rhinological and Otological Society, Inc. Long-Term Hearing Results in Gamma Knife Radiosurgery for Acoustic Neuromas Matthew L. Bush, MD; Jennifer B. Shinn, PhD; A. Byron Young, MD; Raleigh O. Jones, MD Objectives: There are many studies that have ex- amined functional outcomes following Gamma Knife treatment; however, few have reported long-term audio- metric data. This study analyzed the long-term hearing results of Gamma Knife radiosurgery in the treatment of acoustic neuromas. Study Design: Retrospective cohort study. Methods: Seventeen patients were selected from our acoustic neuroma Gamma Knife registry of 113 pa- tients treated from 1991 to 2005. Pretreatment audio- grams were analyzed for pure-tone average and word recognition scores and assigned a Gardner-Robertson classification score (GRC). Either a current audiogram was obtained or the most recent audiogram (if the patient was lost to follow-up) was reviewed from clinic charts and these were compared with the preoperative results. Au- diometric data of the pre- and posttreatment normal ear were obtained and used as the patient’s own control. Results: The tumor size ranged from 0.5 to 2.8 cm (mean, 1.33 cm) and patients received a range of 12.5–16 Gy (mean, 13.82 Gy) to 50% isodose line. Patient follow-up ranged from 3 to 82 months with a mean of 33.6 months. Pretreatment pure-tone average for the in- volved side group was 30.6 dB HL with a word recog- nition score of 74%. Pretreatment mean GRC was 1.76. posttreatment pure-tone average for the group was 59.7 dB HL with a word recognition score of 37%. posttreatment mean GRC was 3.29. Comparing pre- versus post-Gamma Knife radiosurgery results on the treatment ear, means were statistically significantly different for both pure-tone average and word recogni- tion scores, based on a paired-samples t test (P  .001 for both). The group “normal” ear pure-tone average was 14 dB HL and 17.75 dB HL pre- and posttreat- ment, respectively. Normal ear pre- and posttreatment word recognition score and GRC were 93% and 98%, and 1.13 and 1.31, respectively. Conclusion: Gamma Knife radiosurgery remains a noninvasive treatment option for patients with acoustic neuromas; however, they may experience a delayed hear- ing loss. Of those patients with useful audition pretreat- ment, 42% maintained useful hearing posttreatment. Key Words: Gamma Knife, acoustic neuroma, audi- ometry, radiosurgery. Laryngoscope, 118:1019 –1022, 2008 INTRODUCTION Acoustic neuromas are benign tumors originating from Schwann cells of the vestibular portion of the eighth cranial nerve. These tumors are known to cause progres- sive dysfunction of the seventh and eighth cranial nerves; however, many small tumors can remain asymptomatic. Traditionally, acoustic neuromas have been treated sur- gically, but carry significant morbidity including facial paralysis and hearing loss. Earlier diagnoses assisted by enhanced imaging and improved surgical techniques have improved postoperative functional outcomes. To decrease morbidity and mortality, as well as increase facial nerve and hearing function, less invasive modalities have grad- ually emerged. Radiotherapy has evolved as a legitimate treatment option for halting acoustic neuroma growth over the last half century. Leksell 1 first described acoustic neuroma radiation therapy in 1951. It has since developed into two main treatment routes: stereotactic radiosurgery and stereotac- tic radiotherapy. The fundamental difference between the two is that stereotactic radiosurgery involves a single high dose of radiation directed at the tumor, while stereotactic radiotherapy involves fractionated doses of radiation. Lin- ear accelerator and Gamma Knife radiosurgery (GKRS) comprise the two most popular forms of unfractionated radiation in the treatment of acoustic neuromas. Gamma Knife radiosurgery was introduced in 1969 and has been reported to range from 50% to 83% 2–6 successful at pre- serving hearing. The Gardner-Robertson classification 7 (GRC) is commonly used to describe functional hearing in these studies (Table I). This grading scale categorizes auditory function into five groups based on pure-tone av- erage (500, 1000, and 2000 Hz) and word recognition From the Departments of Surgery [Otolaryngology] (M.L.B., J.B.S., R.O.J.) and Neurosurgery (A.B.Y.), University of Kentucky College of Medi- cine, Lexington, Kentucky, U.S.A. Editor’s Note: This Manuscript was accepted for publication January 28, 2008. Selected as the 2008 First Prize, G. Slaughter Fitz-Hugh Southern Section Resident Research Award. Presented at the Southern Section Triological Society Meeting, Na- ples, Florida, January 12, 2008. Send correspondence to Matthew L. Bush, MD, University of Kentucky College of Medicine, Otolaryngology–HNS, 800 Rose Street, Suite C-236, Lexington, KY 40536-0293, U.S.A. E-mail: matthew.bush@uky.edu DOI: 10.1097/MLG.0b013e31816b8cc7 Laryngoscope 118: June 2008 Bush et al.: Gamma Knife Hearing Results 1019