To evaluate the sylvian fissure plateau by sylvian fissure plateau angle (SFPA) and explore the cut-off value of the SFPA in screening for fetal cortical developmental abnormalities.

From June 2018 to July 2020, a prospective ultrasound evaluation was conducted on 180 normal and 3 abnormal singleton pregnant women at 23-28 weeks of gestation in Shenzhen Maternity and Child Healthcare Hospital. All cases were assessed in three axial planes of the fetal brain (transthalamic, transventricular, and transcerebellar) using transabdominal two-dimensional images. The SFPA of all cases was measured between the brain midline (BM) and a line drawn along the sylvian fissure plateau. Non-parametric test was used to compare the differences of the measured SFPA values on the three axial planes. Intraclass correlation coefficient (ICC) was used for assessing the intra- and inter-observer repeatability of the SFPA measurements.

The SFPA in normal cases in the transthalamic, transventricular, and transcerebellar planes were all greater than 0°, while in abnormal cases they were smaller than 0°. However, there was no major difference in the angles measured on the transthalamic and transventricular planes (8.28°±3.00° vs 7.98°±2.86°, P>0.05). There was a major difference in the SFPA on the transcerebellar plane (10.20°±3.46°) and transthalamic/transventricular plane (H=-87.458 and -103.208, respectively, P<0.05). The intra- and inter-observer ICC were excellent at 0.971 (95% confidence interval [CI]: 0.945-0.984) and 0.936 (95%CI: 0.819-0.979), respectively.

The SFPA of normal cases in the three axial views are stable at 23-28⁺⁶weeks of gestation and 0° may be a good cut-off value for evaluating abnormal SFPA. We recommend the SFPA on the transthalamic plane to be used to evaluate the sylvian fissure in clinical work.