Prenatal Evaluation of the Fetal Tympanic Ring Using Transverse Transoccipital Ultrasonographic Sections: A Diagnostic Study.

Objective: To establish normal fetal tympanic ring anterior-posterior diameter (TRAPD) references (12-31 + 6 weeks), analyze correlations with growth parameters, and validate TR's diagnostic utility for external auditory meatus (EAM) abnormalities.

Methods: This retrospective study analyzed 722 fetuses (704 normal, 18 abnormal) undergoing prenatal ultrasound (July 2020-August 2024). TRAPD was measured via transverse transoccipital plane imaging. Normal group data were stratified by gestational age (GA) to develop TRAPD references. TRAPD trends and correlations with GA, biparietal diameter (BPD), head circumference (HC), and auricular dimensions (ear length [EL] and ear width [EW]) were analyzed. A predictive model for EAM abnormalities was constructed.

Results: TRAPD increased nonlinearly with GA, stabilizing at 30 + 5 weeks. TRAPD correlated strongly with GA (r = 0.914), BPD (r = 0.893), EL (r = 0.904), and EW (r = 0.914; all P < .001). AUCs for TRAPD, EL, EW, and the combined model in predicting EAM anomalies were 1.000, 0.867, 0.922, and 1.000, respectively (99.78% accuracy). A bilateral TRAPD mean of <5.6 mm achieved 100% sensitivity and 99.8% specificity in diagnosing EAM anomalies at GA ≥22 weeks. All 15 EAM atresia cases lacked annular TR structure prenatally; three stenosis cases had TRAPD below the 1st percentile for GA-matched fetuses.

Conclusions: TRAPD references and morphology enable reliable prenatal screening for EAM abnormalities, offering actionable clinical thresholds.