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

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).

Retrospective, cross-sectional analysis.

Single academic medical center.

PCD-CT scans of 86 temporal bones from pediatric patients aged 0 to 14 years without prior otologic surgery or congenital malformations.

Radiological assessment.

Prevalence of ST, STS, and FS classifications (type A, B, C) based on their morphological relationship to the mastoid segment of the facial nerve.

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.

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).