Bone-conduction hyperacusis induced by superior canal dehiscence in human: the underlying mechanism

Abstract

Our ability to hear through bone conduction (BC) has long been recognized, but the underlying mechanism is poorly understood. Why certain perturbations affect BC hearing is also unclear. An example is BC hyperacusis (hypersensitive BC hearing)—an unnerving symptom experienced by patients with superior canal dehiscence (SCD). We measured BC-evoked sound pressures in scala vestibuli (PSV) and scala tympani (PST) at the basal cochlea in cadaveric human ears, and estimated hearing by the cochlear input drive (PDIFF = PSV – PST) before and after creating an SCD. Consistent with clinical audiograms, SCD increased BC-driven PDIFF below 1 kHz. However, SCD affected the individual scalae pressures in unexpected ways: SCD increased PSV below 1 kHz, but had little effect on PST. These new findings are inconsistent with the inner-ear compression mechanism that some have used to explain BC hyperacusis. We developed a computational BC model based on the inner-ear fluid-inertia mechanism, and the simulated effects of SCD were similar to the experimental findings. This experimental-modeling study suggests that (1) inner-ear fluid inertia is an important mechanism for BC hearing, and (2) SCD facilitates the flow of sound volume velocity through the cochlear partition at low frequencies, resulting in BC hyperacusis.

Endoscope-Assisted Superior Semicircular Canal Dehiscence Repair: Single Institution Outcomes

“…However, dehiscence location has previously been shown to not influence AC threshold, ABG, or inner-ear sound transmission in cadaveric temporal bones-which have been shown to approximate the soundtransmission mechanics in SCD patients. [17][18][19] While the location of dehiscence may be correlated to the amount of hearing loss at 250 Hz, we did not find this to be the casealthough this may be the result of a skewed sample size as only 1 patient had a complete "downslope" defect. [20][21][22] This study has several limitations.…”

First‐Side and Second‐Side Repair of Bilateral Superior Canal Dehiscence

“…Among these patients, we suspect that dehiscence repair, despite mechanically narrowing the ABG and curtailing the BC-hyperacusis Laryngoscope 134: April 2024 Yang et al: First-Side versus Second-Side Repair effect, may not have completely eliminated the abnormal passage of acoustic energy through the third window. 22 Hence, surgery on the contralateral side would likely also not yield symptom resolution. The precise mechanism responsible for our observation warrants further research.…”

Buegangsdehiscens

“…De e regnes som den sannsynlige årsaken til både det mekaniske hørselstapet og vertigo utløst av trykk og lyd. Samtidig blir vaesken i det indre øret mer bevegelig, slik at vibrasjoner i skallen (inkludert benledet lyd) forårsaker unormalt kraftig stimulering av cochlea (6). Illustrasjon: Frederik Kragerud Goplen.…”

“…Illustrasjon: Frederik Kragerud Goplen. Den unormalt kraftige opplevelsen av benledet lyd (konduktiv hyperakusis) forklares vanligvis av at cochleas reduserte impedans gir økt følsomhet for vibrasjoner i hodeskallen (6).…”