Anatomical Variations of the Retrotympanum in Patients Younger Than 15 Years: A Photon-counting Detector CT Study

OBJECTIVE: To investigate the prevalence of radiologic classifications of the sinus tympani (ST), subtympanic sinus (STS), and facial sinus (FS) in a pediatric population using ultra-high-resolution photon-counting detector CT (PCD-CT). STUDY DESIGN: Retrospective, cross-sectional analysis. SETTING: Single academic medical center. PATIENTS: PCD-CT scans of 86 temporal bones from pediatric patients aged 0 to 14 years without prior otologic surgery or congenital malformations. INTERVENTION: Radiological assessment. MAIN OUTCOME MEASURES: Prevalence of ST, STS, and FS classifications (type A, B, C) based on their morphological relationship to the mastoid segment of the facial nerve. RESULTS: For the ST, type C was the most frequent classification, observed in 49 of 86 cases (57%), with its prevalence being particularly high in infants (86%). For the STS, Type A was the most common, found in 66 of 86 cases (78%). Similarly, for the FS, type A was the most prevalent, identified in 45 of 86 cases (52%). The predominance of type A for both the STS and FS was a consistent trend across all pediatric age groups. CONCLUSIONS: The pediatric retrotympanum is characterized by a high prevalence of deep, posteriorly extended (Type C) ST, which differs significantly from established adult anatomy. In contrast, the STS and FS are predominantly shallow (type A).