Third-window anomalies in children: an imaging-based educational review

Third-window anomalies represent a heterogeneous group of inner ear disorders characterized by abnormal openings in the bony otic capsule, resulting in altered cochlear and vestibular fluid mechanics. By creating an alternative pathway for inner ear fluid motion due to a new opening in addition to the oval and round windows, these lesions disrupt normal sound transmission and vestibular function. In pediatric patients, recognition of third-window anomalies is particularly important, as early and accurate diagnosis supports appropriate clinical assessment and management. High-resolution computed tomography of the temporal bone is the primary imaging modality for evaluating third-window anomalies, enabling detailed assessment of the bony labyrinth. However, many of these abnormalities are subtle and may be underestimated or misinterpreted on standard axial images. The use of anatomy-oriented multiplanar reconstructions tailored to the suspected defect significantly improves lesion conspicuity and diagnostic confidence. This educational review summarizes the anatomic and pathophysiologic principles underlying third-window phenomena in children and illustrates the imaging features of major entities, including semicircular canal dehiscence, enlarged vestibular aqueduct, and less common cochlear dehiscence. The aim is to provide a clear and practical imaging-based framework to support radiologists involved in the evaluation of pediatric inner ear abnormalities.