Abstract
Defective acoustic transmission in the cochlea is closely related with various auditory and vestibular symptoms. Among them, semicircular canal dehiscence (SCD) with a defective semicircular bone is typical. Currently, the pathogenesis of SCD is usually explained by the third window hypothesis; however, this hypothesis fails to explain the variability in the symptoms and signs experienced by superior SCD (SSCD) patients. We evaluated the mechanism of hearing loss in a guinea pig model of bony dehiscence with various sizes and locations along the superior semicircular canal. Auditory brainstem responses (ABRs) and laser Doppler velocimetry were used to measure hearing loss and vibration changes before and after fenestration, as well as after restorative patching. ABR thresholds at low frequencies (e.g., 1000 Hz) increased after fenestration and decreased back to the normal range after we repaired the defect. Energy leakage from the surgically introduced third window was detected in the range of 300–1500 Hz, accompanied by increased vibration at the umbo, stapes head, and the dehiscence site, while decreased vibration was observed at the round window membrane in the same frequency range. After the patching procedure, the deviant vibrations were recovered. The degree of postfenestration energy leakage was proportional to the size of fenestration and the proximity of the fenestration site to the oval window. These results suggest that the bony fenestration of the superior semicircular canal mimics the hearing loss pattern of patients with SSCD. The decrease in perilymph wave impedance likely accounts for the auditory changes.
Highlights
Superior semicircular canal dehiscence (SSCD), initially reported by Minor et al in 1998 [1], is a clinical entity associated with vestibular symptoms typically evoked by sound and pressure stimuli
We have done the whole-mount immunostaining with phalloidin, peripherin, and Ctbp2 in the apical (S1: A, D, and G), middle (S1: B, E, and H), and midbasal (S1: C, F, and I) turns of the cochlear in the surgically prepared guinea pigs, which showed the normal structure of hair cells, neural nerves, and synapses
The laser Doppler velocimetry (LDV) has become a popular device for measuring sound-induced tympanic membrane (TM) velocity in healthy ears and ears with conductive hearing loss for diagnostic purposes in the clinic [16, 17]
Summary
Superior semicircular canal dehiscence (SSCD), initially reported by Minor et al in 1998 [1], is a clinical entity associated with vestibular symptoms typically evoked by sound and pressure stimuli. Temporal-bone histopathological studies suggest that the superior canal of 1-2% of the population has abnormally thin overlying bone. Disruption of this thin layer (caused by trauma or pressure from the overlying temporal lobe of the brain) may trigger both symptoms and signs. Because patients show various clinical symptoms and many of them did not undergo highresolution CT scans, SSCD is likely to be greatly underdiagnosed [2]. Some patients exhibit conductive hearing loss at low frequencies without vestibular symptoms. Most previous investigations have focused on clinical symptoms and treatments [3,4,5]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
