Prenatal Diagnosis and Clinical Outcomes of Isolated Mega Cisterna Magna.

Objective: The study aimed to investigate the clinical outcomes of fetuses diagnosed with isolated mega cisterna magna in utero. Methods: A multicenter retrospective cohort study was conducted across 18 university hospitals from 2010 to 2019. Cases diagnosed with isolated mega cisterna magna, defined as a cisterna magna >10 mm with a normal cerebellar vermis and no cystic dilation of the fourth ventricle, were included. Cases with other central nervous system (CNS) anomalies, extra-central nervous system anomalies, chromosomal abnormalities, or congenital infections were excluded. Maternal demographics, prenatal findings, delivery outcomes, and postnatal outcomes were analyzed. Results: The mean gestational age at initial diagnosis was 28.6 ± 3.9 weeks, and the mean anteroposterior diameter of the cisterna magna was 12.5 ± 3.2 mm. Of the 71 cases initially assessed, 48 (67.6%) showed self-regression in utero. Postnatally, 13 cases (18.3%) had persistent isolated mega cisterna magna, whereas 10 cases (14.1%) were diagnosed with other central nervous system anomalies. Among the persistent isolated mega cisterna magna cases, one child exhibited delayed neurodevelopment. There was a higher incidence of isolated mega cisterna magna in male fetuses, which exhibited a significantly larger mean cisterna magna diameter compared with female fetuses (P = .045). Conclusion: Male fetuses exhibited a higher incidence of isolated mega cisterna magna compared with female fetuses and had larger anteroposterior diameters of the cisterna magna. The study demonstrated favorable neurodevelopmental outcomes associated with isolated mega cisterna magna, with self-regression observed in two-thirds of the cases. However, consecutive prenatal and postnatal evaluations for additional central nervous system or extra-central nervous system malformations need to be performed, considering the differences between prenatal and postnatal diagnoses.