Gestational Growth Dynamics of the Falcine Sinus in Fetal Vein of Galen Malformation

BACKGROUND AND PURPOSE: Vein of Galen malformation (VOGM) is the most common fetal cerebrovascular anomaly, charactered by arteriovenous shunting between choroidal arteries and the persistent median prosencepahlic vein of Markowski. A widened embryonic falcine sinus (FS) is associated with postnatal hemodynamic instability and adverse outcomes, with a threshold width of >7mm used as an inclusion cutoff for a current fetal surgical trial. However, growth dynamics of the FS during gestation have not been studied, and it is unknown whether narrower early measurements predict later enlargement to 7 mm, and thereby ultimately to poor clinical outcome. This study aims to demonstrate longitudinal fetal FS growth and ascertain whether early measurements predict an ultimate FS width > 7mm before birth, and thereby high risk of poor clinical outcome. MATERIALS AND METHODS: We retrospectively reviewed all fetal patients diagnosed radiographically with VOGM at Boston Children's Hospital (Sep. 2002 - Aug. 2025), including those with ≥2 fetal MRI scans with measurable FS width. Two pediatric neurointerventionalists independently reviewed each scan, and the mean values were recorded for analysis. Longitudinal changes were analyzed using generalized estimating equations to account for repeated measures. Predictive performance for final FS > 7mm was assessed using receiver operating characteristic. RESULTS: Thirty-five fetuses met inclusion criteria (20-38 weeks' gestation; median 31 weeks). Mean FS width increased from 4.9mm before 28 weeks to 7.4mm between 32-35 weeks and rose linearly with gestational age by 0.23mm per week (p < 0.001). Predictive accuracy for final FS > 7 mm improved with gestation, reaching discrimination between 33-36 weeks (AUC = 0.93-0.98). A FS width > 4.5mm before 34 weeks predicted final FS > 7mm with 94% sensitivity and 80% specificity (AUC = 0.956, 95% CI: 0.87-1.00). By 35 weeks, a FS > 6.1mm had 95% sensitivity and 100% specificity (AUC = 0.979, 95% CI: 0.93-1.00). CONCLUSIONS: The fetal FS enlarges across gestation in VOGM. A FS width > 4.5mm by 34 weeks serves as an early predictor of future FS width >7mm. Measurement of FS width on fetal MRI may assist in prenatal counseling, risk stratification, and clinical decision-making for fetuses with VOGM.