Multiple midline brain anomalies in a CMV-exposed fetus with successful surgical management: a case report and literature review

Introduction: Congenital arachnoid cysts (ACs) are cerebrospinal fluid collections resulting from abnormal splitting of the arachnoid membrane during embryogenesis. They may occur as isolated lesions or in association with other central nervous system (CNS) malformations. Congenital cytomegalovirus (cCMV) infection is a leading infectious cause of neurodevelopmental impairment and may contribute to complex CNS anomalies. Presentation of case: A term male infant was diagnosed prenatally at 30 weeks with midline cystic lesions, ventriculomegaly, and absent corpus callosum. Postnatal magnetic resonance imaging confirmed a large left temporal interhemispheric AC with complete agenesis of the corpus callosum, colpocephaly, absent cavum septi pellucidi, subcortical heterotopia, and mega cisterna magna. Maternal serology indicated past CMV infection, and postnatal urine PCR confirmed congenital CMV infection. Despite progressive cyst enlargement, he remained asymptomatic until neurosurgical fenestration at 5 months, after which imaging showed good decompression and neurodevelopment remained normal. Discussion: The coexistence of a large AC with multiple major structural brain anomalies and cCMV exposure is exceptionally rare and typically portends a poor prognosis. This case demonstrates that even in the presence of several high-risk features, favorable early neurodevelopmental outcomes are possible. Early detection through prenatal imaging, close postnatal monitoring, and timely surgical intervention were critical to this outcome. Conclusion: A large AC with multiple associated CNS anomalies does not invariably lead to severe neurodevelopmental impairment. This case reinforces the heterogeneity of outcomes, especially the early ones, and shows the importance of early diagnosis, tailored multidisciplinary management, and long-term developmental follow-up to guide family counseling and clinical decision-making.