Third Window Lesions.

Third window abnormalities are bony defects of the inner ear that enable abnormal communication with the middle ear and/or cranial cavity. Vestibular symptoms include vertigo and nystagmus induced by loud noises or increases in pressure. Auditory symptoms involve "pseudo-conductive" hearing loss with a low-frequency air-bone gap at audiometry, resulting from decreased air and increased bone conduction. High-resolution temporal bone computed tomography is the first-line imaging modality for evaluation of third window pathology and is critical for accurate diagnosis and management. This article reviews the fundamental mechanisms of the third window phenomenon and describes imaging findings and differential diagnosis.