Nomograms of the Fetal Sylvian Fissure and Insular Lobe throughout Gestation: A Multicentric, Ultrasonographic Cross-Sectional Study

Introduction: Anomalies in cortical development are often associated with an adverse outcome, but prenatal diagnosis is often impeded by the limited knowledge about normal sulci biometries throughout fetal brain development. Our aim was to provide two-dimensional ultrasonographical (2D US) nomograms of the depth of the Sylvian fissure (SF) and insular lobe (IL), as well as of the SF ratio throughout gestation in a large number of fetuses. Materials and Methods: This was a prospective cross-sectional study of 329 normal singleton pregnancies. Measurements of the SF, IL, and SF ratio were obtained in a standard transthalamic plane of the fetal head. The SF ratio was defined as SF\SF + IL. All measurements were expressed by regression equations as a function of gestational age (GA) according to the method described by Royston and Wright. The first 38 measurements were repeated twice by 2 examiners to assess the reproducibility through the intraclass correlation coefficient (ICC). Results: A significant correlation was found between GA and SF (r = 0.79; p < 0.0001) as well as IL (r = 0.77; p < 0.0001). Similarly, the SF ratio also showed a significant correlation with GA (r = 0.39; p < 0.0001). When interobserver variability was assessed, ICC was 0.97. Conclusions: Prenatal 2D US measurements of SF and IL as well as the SF ratio may be feasible and reproducible using a standard view of the fetal head. Our nomograms may be used as a reference for assessing cortical development throughout pregnancy.