Air-Bone Gap Component of Inner-Ear Origin in Audiograms of Cochlear Implant Candidates *†Joseph Attias, ‡§David Ulanovski, *Rafael Shemesh, §kLiora Kornreich, ‡§Benny Nageris, ‡§Michal Preis, †Miriam Peled, †Michal Efrati, and ‡§Eyal Raveh *Department of Communication Sciences and Disorders, University of Haifa, Haifa; ÞInstitute of Audiology and Clinical Neurophysiology, þDepartment of Otorhinolaryngology, Schneider Children’s Medical Center of Israel and Rabin Medical Center, Petach Tikva; §Sackler School of Medicine, Tel Aviv University, Tel Aviv; and kDepartment of Imaging, Schneider Children’s Medical Center of Israel and Rabin Medical Center, Petach Tikva, Israel Background: Experimental studies have shown that creating a window in the bony cover of the cochlea and vestibular parts of the inner ear, with preservation of membranous and middle-ear functions, induces an air-bone gap (ABG). This study sought to determine if a similar mechanism explains the ABG frequently observed in audiograms of cochlear implant candidates. Method: The study group included 47 candidates for a cochlear implant (94 ears) attending a university-affiliated tertiary medical center who had an ABG component in the audiogram in the absence of external or middle-ear abnormalities. Air- and bone- conduction thresholds on pure-tone audiometry were analyzed for 250 to 8,000 Hz and 250 to 4,000 Hz, respectively. In the 25 patients operated on during the study period, differences in the ABG and in cerebrospinal fluid (CSF) leak were com- pared between those with and without anomalies on computed tomography. Results: Imaging revealed an abnormal inner-ear structure in 46% of cases, mostly a large vestibular aqueduct, alone or combined with other cochlear or vestibular malformations. ABG was evident over high and low frequencies and was significantly larger at low frequencies and in ears with structural anomalies. A high rate of CSF leak was observed in patients with an ABG and structural anomalies imaging as well as in those with an ABG and normal imaging findings. Conclusion: In cochlear implant candidates, the presence of a third window could cause an ABG because of stapes motion- induced shunting of acoustic energy outside the cochlear duct in response to air-conducted stimuli while bone conduction is preserved. Key Words: Air-bone gapsVCochlear implantV Cerebrospinal fluid leakVInner ear anomaliesVThird window. Otol Neurotol 33:512Y517, 2012. Our clinical experience in the Cochlear Implant Pro- gram of a tertiary pediatric medical center indicates that air-bone gaps (ABGs), primarily in the low frequencies, are common in candidates for cochlear implants with normal middle-ear function. Typically, the audiogram shows severe-to-profound hearing loss at high frequen- cies and better auditory thresholds at low frequencies. According to various studies, 20% to 30% of patients with profound sensorineural hearing loss have inner-ear abnormalities (1Y5). In a recent series of animal studies, our group found that creating a window in the bony cover of the cochlea and vestibular parts of the inner ear, with preservation of membranous and middle ear functions, induced an ABG on auditory brainstem response (ABR) tests (6Y9). To explain these findings, we suggested that when a third window is present in the inner ear, a portion of the acoustic energy introduced by stapes motion during air conduction is shunted away from the cochlea through vibrations of the additional membrane, thereby increasing the air-conduction threshold. However, because bone- conducted vibrations are induced by multiple forces of compression and inertia from bony, membranous, and fluid structures in the cranium, these would act in con- junction with the vibrations of the third membrane, pre- serving or even improving bone-conduction thresholds. The deterioration in air-conduction threshold, together Address correspondence and reprint requests to Joseph Attias, D.Sc., Institute of Audiology and Clinical Neurophysiology, Schneider Chil- dren’s Medical Center of Israel, Petach Tikva 49202, Israel; E-mail: attiasj@netvision.net.il The authors disclose no conflicts of interest. No funding was received for this study. Otology & Neurotology 33:512Y517 Ó 2012, Otology & Neurotology, Inc. 512 Copyright © 2012 Otology & Neurotology, Inc. Unauthorized reproduction of this article is prohibited.