Posterior Fossa Anomalies: A Detailed Review of Prenatal Findings and Management from a tertiary care centre

Abstract

Objective: Posterior fossa anomalies (PFAs) encompass a spectrum of central nervous system malformations affecting the cerebellum, brainstem, and surrounding cerebrospinal fluid spaces. This study evaluates the prenatal diagnosis, genetic findings, and pregnancy outcomes of PFAs in a tertiary care setting in India. Methods: A retrospective analysis was conducted on 35 cases of PFAs diagnosed via prenatal ultrasound and fetal MRI between January 2023 and May 2024. Anomalies were classified based on standard criteria, and genetic testing (karyotypte, chromosomal microarray analysis and whole exome sequencing) was offered. Pregnancy outcomes, including termination, live birth, and neonatal survival, were documented, with short-term neurodevelopmental follow-up conducted via telephonic inquiries. Results: The most common PFAs identified were Vermian Agenesis/Hypoplasia (VA/VH) and Cerebellar Hypoplasia (CH), each accounting for 25.71% of cases, followed by Dandy-Walker Malformation (20%). Isolated PFAs were observed in 37.14% of cases, while 62.85% had additional anomalies. Genetic testing was performed in 74.2% of cases, revealing variants in 5.71%. Karyotyping was performed in all tested cases and yielded normal results, while additional molecular testing with chromosomal microarray analysis (5 cases) and whole-exome sequencing (3 cases) detected clinically relevant variants in selected fetuses with posterior fossa anomalies. Among the 35 pregnancies, 65.71% opted for termination, facilitated by the Medical Termination of Pregnancy (MTP) Act, particularly for cases diagnosed beyond 24 weeks of gestation. Of the 9 live births, 2 neonates with vermian hypoplasia (5.71%) died within one month, while 6 (17.14%) had normal developmental milestones at 6 months including 6 babies with mega cisterna magna and one with an arachnoid cyst. One infant exhibited delayed milestones. Conclusion: PFAs present with diverse prognostic implications, necessitating detailed imaging, genetic evaluation, and individualized counseling. The MTP Amendment Act, played a crucial role in providing extended access to termination in pregnancies with severe PFAs and poor prognoses.