Clinical, Experimental, and Theoretical Investigations of the Effect of Superior Semicircular Canal Dehiscence on Hearing Mechanisms

Abstract

The results suggest that superior semicircular canal dehiscence can affect hearing function by introducing a third window into the inner ear.

The effect of superior canal dehiscence on cochlear potential in response to air-conducted stimuli in chinchilla

“…Air-conducted sound causes a stapes volume velocity, which is partially shunted through the superior semicircular canal when there is a dehiscence. This shunting leads to a decrease in the stimulus to the cochlea and diminishes the round window velocity (adapted from Rosowski et al, 2004). Table 1 The mean, SD (column 2) and significance (column 3) of the dB difference of the cochlear potential magnitude between the intact (pre-SCD) condition and after the introduction of the dehiscence (post-SCD) (n = 11) NS NS denotes cases where the null hypothesis that the manipulations do not alter the CP is accepted at the 5% significance level.…”

“…Previous reports have investigated the role of SCDs on auditory sensitivity in response to boneconducted (BC) sound stimuli in an animal model Rosowski et al, 2004;Sohmer et al, 2004). These studies demonstrated that sensitivity to BC stimuli increases after the introduction of a dehiscence and that the increase is greatest at frequencies below 2 kHz .…”

“…The air-bone gap (calculated as the difference between the bone-conducted and air-conducted thresholds) observed clinically in patients with SCD syndrome has been qualitatively explained by the 'third-window hypothesis' (Minor et al, 1998;Rosowski et al, 2004) that proposes that some of the volume velocity produced by the stapes in response to air-conducted (AC) stimuli is shunted away from the cochlea, through the dehiscent canal. This shunt causes a reduction in the flow of AC sound energy into the cochlea, indicated by increases in AC hearing thresholds.…”

A possible third window for bone conducted hearing: Cochlear aqueduct vs. vestibular aqueduct

“…Here, 'x' represents the length of the BM from the stapes. For example, P a (5) indicates that the P a at the position of 5 mm from the base of the BM.…”

“…Therefore, a third window (TW), which is another fluid pathway in the cochlea except the OW and RW, was suggested as a possibile factor to explain the asymmetry of the volume velocity ratio. However, in spite of many studies for potential TWs [1,4,5], it is still unclear which opening in the real cochlea acts as the TW causing the asymmetry of the ratio. In order to further investigate the effect of the TWs on the asymmetry of the volume velocity ratio, we used a 3-D finite-element (FE) human-ear model consisting of the middle ear and the cochlea.…”