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THIRD WINDOW DISORDERS

*Third Window Disorders of the Bony Labyrinthine* Third window disorders are conditions that affect the bony labyrinth of the inner ear, creating an abnormal "third window" within the inner ear's structure. Normally, there are two main "windows" in the bony labyrinth: the oval window and the round window. These structures play crucial roles in hearing and balance. A third window disrupts the normal fluid mechanics of the inner ear, leading to auditory and vestibular symptoms. Anatomy of the Bony Labyrinth The bony labyrinth is a complex, rigid, bony structure within the temporal bone of the skull that houses the cochlea, vestibule, and semicircular canals. These components are filled with fluid (perilymph and endolymph) and are crucial for hearing and balance. The normal pathways of sound and pressure changes in the inner ear are mediated through the oval and round windows, allowing proper transmission of sound and balance signals to the brain. Pathophysiology of Third Window Disorders A third window disorder involves an abnormal opening in the bony labyrinth, leading to: Abnormal flow of inner ear fluid-disrupting normal pressure dynamics. Loss of energy in sound transmission-leading to conductive hearing loss. Altered vestibular responses- resulting in balance disturbances and vertigo. _ Common Third Window Disorders 1. Superior Semicircular Canal Dehiscence (SSCD);- 2. Enlarged Vestibular Aqueduct Syndrome (EVAS):- 3. Perilymphatic Fistula:- 4. X-Linked Stapes Gusher Syndrome: 5;-Dilated Internal Auditory Meatus (IAM)