Abstract
Third window abnormalities are defects in the integrity of the bony structure of the inner ear, classically producing sound-/pressure-induced vertigo (Tullio and Hennebert signs) and/or a low-frequency air-bone gap by audiometry. Specific anatomic defects include semicircular canal dehiscence, perilabyrinthine fistula, enlarged vestibular aqueduct, dehiscence of the scala vestibuli side of the cochlea, X-linked stapes gusher, and bone dyscrasias. We discuss these various entities and provide key examples from our institutional teaching file with a discussion of symptomatology, temporal bone CT, audiometry, and vestibular-evoked myogenic potentials.
Highlights
Normal sound conduction is transmitted through the oval and round windows, which serve as fluid interfaces between air in the middle ear and perilymphatic fluid spaces of the inner ear
At Massachusetts Eye and Ear Infirmary, 5 patients (8 ears) with posterior semicircular canal dehiscence were included in the teaching file from 2000 to 2011
At Massachusetts Eye and Ear Infirmary, 43 patients (60 ears) with perilabyrinthine fistula of the semicircular canals, vestibule, and/or scala vestibuli side of the cochlea were included in the teaching file from 2000 to 2011
Summary
Normal sound conduction is transmitted through the oval and round windows, which serve as fluid interfaces between air in the middle ear and perilymphatic fluid spaces of the inner ear. Potential third windows include bony dehiscence of the semicircular canals, enlargement of the opening of the vestibular aqueduct, dehiscence of the scala vestibuli side of the cochlea, and abnormal bony thinning between the cochlea and vascular channels.
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