Supplementary Material for: Fetal Sylvian Fissure Charts to Evaluate the Development of Fetal Brain using Prenatal MRI

Objective: To assess fetal sylvian fissure (SF) development via MRI to early detect cortical abnormalities by quantifying the morphological characteristics.
Methods: This study retrospectively evaluated the prenatal MRI of 324 normal singleton pregnancies at 22-38+6 weeks of gestation (GA). Biparietal diameter (BPD), insula depth (ID), sylvian fissure width (SFW), uncovered insula length (UIL), uncovered insula rate (UIR), sylvian fissure depth (SFD), sylvian fissure anterior depth (SFAD), sylvian fissure posterior depth (SFPD), sylvian fissure superior depth (SFSD) and sylvian fissure inferior depth (SFID) were obtained in the axial and coronal positions. Reproducibility was assessed using 40 cases and verified using the intraclass correlation coefficient (ICC). Correlations with GA were analyzed, and growth charts were drawn using optimal curve fitting. A paired-sample t-test was used to compare the left-right disparities, and an independent-sample t-test was used to compare the differences between SFAD and SFPD, and between SFID and SFSD. To evaluate clinical utility, we applied the normative charts to two fetuses with genetically confirmed cerebral cortical malformations.
Results: Interobserver agreements were reproducible (ICC: 0.870-0.988). Reference ranges for sylvian fissure parameters were established. All SF parameters showed a significant correlation with GA (|r| = 0.386 - 0.965, p < 0.05). Axial measurements showed left-right differences in SFW and UIR. SFPD was longer than SFAD bilaterally (p < 0.05). In comparison, SFID was significantly longer than SFSD only on the left side (p < 0.05). The model detected two genetically confirmed cases of polymicrogyria at 26+6 and 30 weeks of gestation and identified subtle focal structural abnormalities undetectable by routine imaging, revealing widespread asymmetrical sylvian fissure defects.
Conclusion: The development of the sylvian fissure is dynamic throughout gestation and is a reliable feature of fetal cortex gyration. We provide certain reference standards of prenatal MRI to assist in diagnosing abnormal fetal cerebral cortex development.