Isolated Fluid Enlargements of the Posterior Cranial Fossa: Antenatal Diagnosis and Postnatal Outcome: A Series of 53 Cases

Abstract Blake's pouch cyst (BPC), mega cisterna magna (MCM), and arachnoid cyst (AC) are common fluid enlargements of the posterior cranial fossa (PCF) detected prenatally. Differentiating these anomalies on fetal imaging can be difficult, and although they are frequently identified, few studies focus on isolated forms without associated anomalies. This study aims to better characterize isolated PCF fluid enlargements to improve prenatal counseling. We conducted a retrospective, bicentric study of all antenatal diagnoses of isolated fluid enlargements of the PFC between January 2010 and April 2022. Postnatal neurodevelopment was assessed through pediatric neurology follow-up and health records, with a maximum follow-up of 12 years. Children were classified into two groups: normal or delayed psychomotor development. Fifty-three children were included (21 MCM, 20 AC, 12 BPC), with a male preponderance (65%). ACs were associated with larger cisterna magna measurements, distal elevation of the cerebellar tentorium, and mass effect on the vermis. Postnatal imaging was normalized in 8 cases (16%). Forty three children (86%) had normal neurodevelopment. Seven presented with psychomotor delay. Three AC cases (15%) required surgery in the first year due to hydrocephalus. Our study highlights the favorable prognosis of isolated fluid enlargements. Detailed prenatal classification and postnatal monitoring are essential to optimize counseling.