Evaluation of ear structures on fetal MRI: A comparative analysis at 1.5-T and 3-T

To compare the visualization of fetal ear structures on 1.5-Tesla (T) and 3-T fetal MRI (feMRI) using a staging system, and to measure cochlear height (CH) at 3-T.

Between 2009-2024, 147 feMRI examinations were retrospectively evaluated; after excluding 25 suboptimal scans, 122 studies were analyzed (1.5-T = 80; 3-T = 42). The cochlea, vestibule-semicircular canals (V-SCC), middle ear-ossicular chain (ME-OC), and external auditory canal (EAC) were systematically staged by a blinded neuroradiologist. CH was measured on 3-T. Categorical and group comparisons, correlation and ROC analysis were performed.

Mean gestational week (GW) was 29.1 ± 3.7 weeks with no between-group difference (p = 0.101). Staging scores were higher at 3-T for the cochlea and V-SCC (both p < 0.001) and for ME-OC (p = 0.019), with no difference for EAC (p = 0.317). At 3-T, cochlear turns were identifiable in 83.3%, the lateral semicircular canal in 61.9%, and ossicles in 73.8%; at least one EAC was visualized in 71.4%. GW correlated with V-SCC (rₛ=0.220, p = 0.015) and EAC (rₛ=0.330, p < 0.001). ROC analysis identified 29.5 GW as the optimal cutoff for EAC visualization (AUC=0.718; 95% CI, 0.626-0.809; sensitivity, 57.3%; specificity, 75.0%; p < 0.001). At 3-T, CH averaged 5.17 ± 0.53 mm and showed no correlation with GW (r = 0.041, p = 0.794).

Compared with 1.5-T, 3-T feMRI provides superior visualization of inner and middle ear structures, with similar EAC performance. In suspected anomalies, a focused ear assessment within feMRI improves prenatal ear evaluation, alongside ultrasonography.