Investigation of Mechanisms in Bone Conduction Hyperacusis With Third Window Pathologies Based on Model Predictions

Abstract

A lumped element impedance model of the inner ear with sources based on wave propagation in the skull bone was used to investigate the mechanisms of hearing sensitivity changes with semi-circular canal dehiscence (SSCD) and alterations of the size of the vestibular aqueduct. The model was able to replicate clinical and experimental findings reported in the literature. For air conduction, the reduction in cochlear impedance due to a SSCD reduces the intra-cochlear pressure at low frequencies resulting in a reduced hearing sensation. For bone conduction, the reduced impedance in the vestibular side due to the SSCD facilitates volume velocity caused by inner ear fluid inertia, and this effect dominates BC hearing with a third window opening on the vestibular side. The SSCD effect is generally greater for BC than for AC. Moreover, the effect increases with increased area of the dehiscence, but areas more than the cross section area of the semi-circular canal itself leads to small alterations. The model-predicted air-bone gap for a SSCD of 1 mm 2 is 30 dB at 100 Hz that decreases with frequency and become non-existent at frequencies above 1 kHz. According to the model, this air-bone gap is similar to the air-bone gap of an early stage otosclerosis. The normal variation of the size of the vestibular aqueduct do not affect air conduction hearing, but can vary bone conduction sensitivity by up to 15 dB at low frequencies. Reinforcement of the OW to mitigate hyperacusis with SSCD is inefficient while a RW reinforcement can reset the bone conduction sensitivity to near normal.

Current Trends, Controversies, and Future Directions in the Evaluation and Management of Superior Canal Dehiscence Syndrome

“…The low-frequency decrease in air conduction hearing (higher air conduction thresholds) is due to volume velocity shunting via the SCD ( Figure 1B ) ( 9 , 10 ). The low-frequency increase in bone conduction hearing (lower bone conduction thresholds) is due to altered inner-ear volume velocities and pressures in response to vibration of the skull and altered mass of the inner ear fluid as determined recently in Guan et al ( 11 , 18 ).…”

“…ABG has shown to increase with decreasing frequency, and larger ABG is associated with larger SCD size ( 9 , 12 , 48 , 54 ). Furthermore, some SCD patients will have supranormal low frequency (<1 kHz) bone conduction thresholds at −5 to −10 dB HL ( 8 , 11 , 18 , 50 , 53 ). Low-frequency ABG due to SCD are caused by the combined effects of two separate mechanisms verified by consistency of clinical, temporal bone, and computational modeling data.…”

“…Dural pulsations across the dehiscence are the likely cause of pulsatile tinnitus (a common auditory symptom in SCDS patients). The pathophysiology of SCDS remains incompletely understood, especially with regard to the variability in symptomatology among patients, but remains the focus of a number of research studies ( 8 – 11 , 17 , 18 ).…”

Review of Whole Head Experimental Cochlear Promontory Vibration with Bone Conduction Stimulation and Investigation of Experimental Setup Effects

“…Several different pathways have been recognized and suggested as contributors for BC hearing: ear canal sound pressure, middle ear ossicles inertia, inner ear fluid inertia, compression and expansion of inner ear space, and pressure transmission through the skull interior (Stenfelt, 2012a(Stenfelt, , 2015Stenfelt & Goode, 2005a). However, their relative importance is still debated (Stenfelt, 2016(Stenfelt, , 2020.…”

The Effect of Stimulation Position and Ear Canal Occlusion on Perception of Bone Conducted Sound

“…With BC, skull vibrations transmit the sound signals to the cochlea. BC has been suggested to have the following five main transmission pathways (Stenfelt & Goode, 2005a): a) sound radiation in the ear canal that is subsequently transmitted to the cochlea via the middle ear (Stenfelt et al, 2003;Surendran & Stenfelt, 2021); b) inertial motion of the ossicular chain (Stenfelt, 2006;Stenfelt et al, 2002); c) inertial motion of the cochlear fluids (Stenfelt, 2015(Stenfelt, , 2020; d) vibration of the bone around the inner ear leading to compression and expansion of the inner ear space (Stenfelt, 2015); e) sound pressure transmission from the cerebrospinal fluid (Roosli et al, 2016;Sohmer et al, 2000). Moreover, the human head is a complex mechanical system with multiple vibration modes during BC stimulation (Dobrev et al, 2017;Stenfelt & Goode, 2005b).…”