Sonographic Cortical Development and Anomalies in the Fetus: A Systematic Review and Meta-Analysis

The aim of this systematic review is to report the normal cortical development of different fetal cerebral fissures on ultrasound, describe associated anomalies in fetuses with cortical malformations, and evaluate the quality of published charts of cortical fissures. The inclusion criteria were studies reporting development, anomalies, and reference charts of fetal cortical structures on ultrasound. The outcomes observed were the timing of the appearance of different cortical fissures according to different gestational age windows, associated central nervous system (CNS) and extra-CNS anomalies detected at ultrasound in fetuses with cortical malformation, and rate of fetuses with isolated anomaly. Furthermore, we performed a critical evaluation of the published reference charts for cortical development on ultrasound. Random-effect meta-analyses of proportions were used to combine the data. Twenty-seven studies (6875 fetuses) were included. Sylvian fissure was visualized on ultrasound in 97.69% (95% CI 92.0-100) of cases at 18-19, 98.17% (95% CI 94.8-99.8) at 20-21, 98.94% (95% CI 97.0-99.9) at 22-23, and in all cases from 24 weeks of gestation. Parieto-occipital fissure was visualized in 81.56% (95% CI 48.4-99.3) of cases at 18-19, 96.59% (95% CI 83.2-99.8) at 20-21, 96.85% (95% CI 88.8-100) at 22-23, and in all cases from 24 weeks of gestation, while the corresponding figures for calcarine fissure were 37.27% (95% CI 0.5-89.6), 80.42% (95% CI 50.2-98.2), 89.18% (95% CI 74.0-98.2), and 96.02% (95% CI 96.9-100). Malformations of cortical development were diagnosed as an isolated finding at ultrasound in 6.21% (95% CI 2.9-10.9) of cases, while they were associated with additional CNS anomalies in 93.79% (95% CI 89.1-97.2) of cases. These findings highlight the need for large studies specifically looking at the timing of the appearance of the different brain sulci. Standardized algorithms for prenatal assessment of fetuses at high risk of malformations of cortical development are also warranted.