Sylvian fissure angle development on fetal MRI: 22-38 gestational weeks

The objective of the study was to quantify Sylvian fissure angle (SFA) development via fetal magnetic resonance imaging (MRI) and establish the reference range and growth curve during normal pregnancy.

This retrospective cross-sectional study collected 324 singleton fetuses at 22-38 weeks of gestation (GA), without abnormal signs on MRI or chromosomal defects, from January 2022 to December 2023. Six SFAs were defined and measured: Sylvian fissure plateau angle (SFPA), Sylvian fissure anterior rotation angle (SFARA), and Sylvian fissure posterior rotation angle (SFPRA) in the transthalamic axial plane, and SFPA, Sylvian fissure superior rotation angle (SFSRA), and Sylvian fissure inferior rotation angle (SFIRA) in the third ventricular coronal plane. Then, the correlation between the SFAs and GA was analyzed, and the growth curve model was used. Retrospective cortical malformation cases validated the model. The intraclass correlation coefficient (ICC) was used to evaluate interobserver variability of the SFA measurements.

ICC for SFA measurements demonstrated good reliability (0.772-0.976). The bilateral SFARA and SFSRA were significantly positively associated with GA (r = 0.914, 0.926, 0.842, 0.836, left to right, all p < 0.001). The bilateral SFPRA, SFIRA, and SFPA (both axial and coronal views) were negatively associated with GA (r value range: -0.601 to -0.145, all p < 0.001). For each SFA and GA, the quadratic curve has the best goodness of fit. The model detected cortical malformation (genetically confirmed). Except for the SFARA, all SFAs were statistically different between the two sides.

The dynamic development of the fetal SFA can be well evaluated using MRI. The SFA's reference range will enhance the accuracy of fetal brain assessment and offer a quantitative reference framework for identifying deviations suggestive of cortical malformations.