SUPERIOR SEMICIRCULAR CANAL DEHISCENCE AND BONE CONDUCTION IN CHINCHILLA

Abstract

Superior semicircular canal dehiscence (SSCD) syndrome is primarily associated with vertigo and disequilibrium induced by loud sounds (Tullio’s phenomenon) and middle-ear pressure changes. SSCD syndrome may also cause increased bone-conduction sensitivity and decreased air-conduction sensitivity leading to an air-bone gap. The abnormalities in both air and bone sensitivities are typically greatest at frequencies below 2 kHz. Understanding the mechanisms that cause this air-bone gap may aid in the diagnosis of SSCD syndrome and in understanding the pathology that causes the symptoms. We examined the effects of SSCD on responses to bone-conduction stimuli in a chinchilla model by measuring the motion of the fluid wit,hin the dehiscence and the cochlear pot,ential. In siirgically itidiiccd dcliiscciiccs wv foulid difrcrci1i~i;d i l io i . io t i l)ci.wc.cn (.lie iiiiicr-ciLr fliiid and t.he adjacerii. boiic i i i response 1.0 boiic-coiidrici.ior1 st.itiiiili for frcqiiciicies froiri 561) 1 lz 2440 Hz. An increase in sensitivity to bone-conducted stimuli (as measured by cochlear potential) near 500 Hz of 8 dB was also found. The sensitivity to bone-conducted stimuli is dependent on the size of the dehiscence. Increased CP in chinchillas with surgically induced SSCD is consistent with lower bone-conduction thresholds in SSCD syndrome patients suggesting that bone-conduction hypersensitivity is an indicator of a SSCD.