Abstract
Third window disorders are structural abnormalities in the bony otic capsule that establish a connection between the middle/inner ear or the inner ear/cranial cavity. Investigated extensively in adults, they have hardly been studied in children. This study is a retrospective study of children (aged 5–17 years) diagnosed with rare third window disorders (third window disorders reported rarely or not reported in children) in a tertiary pediatric vestibular unit in the United Kingdom. It aimed to investigate audiovestibular function in these children. Final diagnosis was achieved by high resolution CT scan of the temporal bones. Of 920 children attending for audiovestibular assessment over a 42 month period, rare third windows were observed in 8 (<1%). These included posterior semicircular canal dehiscence (n = 3, 0.3%), posterior semicircular canal thinning (n = 2, 0.2%), X linked gusher (n = 2, 0.2%), and a combination of dilated internal auditory meatus/irregular cochlear partition/deficient facial nerve canal (n = 1, 0.1%). The majority of them (87.5%) demonstrated a mixed/conductive hearing loss with an air-bone gap in the presence of normal tympanometry (100%). Transient otoacoustic emissions were absent with a simultaneous cochlear pathology in 50% of the cohort. Features of disequilibrium were observed in 75% and about a third showed deranged vestibular function tests. Video head impulse test abnormalities were detected in 50% localizing to the side of the lesion. Cervical vestibular evoked myogenic potential test abnormalities were observed in all children in the cohort undergoing the test where low thresholds and high amplitudes classically found in third window disorders localized to the side of the defects in 28.5%. In the series, 71.4% also demonstrated absent responses/amplitude asymmetry, some of which did not localize to the ipsilesional side. Two children presented with typical third window symptoms. This study observes 2 new rare pediatric third window phenotypes and the presence of a cochlear hearing loss in these disorders. It emphasizes that these disorders should be considered as an etiology of hearing loss/disequilibrium in children. It also suggests that pediatric third window disorders may not present with classical third window features and are variable in their presentations/audiovestibular functions.
Highlights
The human ear consists of 2 mobile normal windows for transmission of sound between the middle and the inner ear, namely the oval window and the round window
The diagnosis of the X linked gusher group was by typical high resolution computerized tomographic scans (HRCT) findings and a typing of the POU3F4 genetic mutation in a family of 2 children with the same mother
In the current study we concentrated on rare third window disorders in children, the definition of which we have described in our Methods section
Summary
The human ear consists of 2 mobile normal windows for transmission of sound between the middle and the inner ear, namely the oval window and the round window. There are other windows called third windows that are present, and these windows connect the inner ear to the cranial cavity, for example, the cochlear aqueduct, the vestibular aqueduct, and the numerous bony channels that conduct the nerves and vessels entering or exiting the inner ear from/to the posterior cranial fossa [1]. Pathological third windows, on the other hand, do interfere with transmission of the cochlear traveling wave generated at the oval window, as these windows do not offer high impedance to acoustic transmission They shunt or deviate the acoustic energy from the middle ear, thereby leading to a drop in air conducted sound thresholds and improve the bone conduction thresholds as they provide an alternate low impedance path, bypassing the oval-round window classical low impedance pathway [1]. These third windows are due to defects in the bony otic capsule
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