This is a prospective, single-arm non-randomized interventional study of fetuses to assess the efficacy and safety of fetal embolization of VOGM. Subjects will receive a one-time study intervention of fetal embolization, at or after 34 weeks of gestation. After delivery, neurological assessments will be performed every 6 months for 2 years (adjusted for gestational age). Data will be compared to historical cohorts.

The study involves a single fetal intervention of maternal transuterine, fetal transcranial torcular puncture and median prosencephalic vein embolization for fetuses with vein of Galen malformations (VOGM) with a falcine sinus (FS) width of >= 7 mm (study population). Detachable platinum coils (Target XL and XXL Detachable Coil, Stryker Neurovascular) will be used to pack the prosencephalic varix. This procedure will take place in an OR at Boston Children's Hospital. Data regarding pre-delivery, delivery and post-delivery status will be collected until the subject is discharged from the hospital. After delivery, neurological assessments will be performed on the child every 6 months for 2 years (adjusted for gestational age). Data will be compared to historical cohorts.

Inclusion Criteria:

1. Pregnant woman carrying a fetus harboring a vein of Galen malformation in whom the straight sinus or falcine sinus draining the prosencephalic varix measures 7 mm or more on fetal MRI (medio-lateral diameter measured at the narrowest point of the sinus along the rostral-caudal axis, assessed on a T2-weighted coronal or axial slice).
2. Fetal gestational age of 34 weeks or more at the time of the planned fetal intervention, as determined by clinical information and evaluation of first ultrasound. The suitability for fetal treatment, in terms of technical/positional factors, will be assessed on a case-by-case basis by the MFM, ultrasonographer, and neurointerventionalist participating in the study.
3. Anatomic diagnosis of fetal vein of Galen malformation. Various cerebrovascular conditions, such as dural sinus malformation and pial arteriovenous fistula, can result in dilated intracranial vascular structures being visualized in utero. Similarly, fetal dilatation of the vein of Galen can occasionally be seen without the presence of an arteriovenous lesion at all, as a benign venous variant. This condition is readily distinguishable sonographically from VOGM by virtue of the presence of dilated arterial feeding pedicles, and by the presence of an arterial waveform within the varix. This study is aimed solely at fetuses with an established diagnosis of vein of Galen malformation.

Exclusion Criteria:

1. Extensive fetal brain parenchymal injury/gliosis, i.e. >10% of supratentorial brain volume (SFP presentation). In some cases, significant bihemispheric cerebral parenchymal injuries are seen at the time of initial fetal diagnosis of vein of Galen malformation (SFP cohort). Such fetuses rarely survive, but if they do, are profoundly neurodevelopmentally impaired: typically blind, mute, quadriparetic, often with unremitting intractable seizures, and permanently bed-bound and uncommunicative. As there is no realistic possibility of achieving a good neurological outcome in such patients, fetuses with diffuse bihemispheric brain injury will be excluded.
2. Irreversible fetal non-brain organ injury (e.g. hydrops fetalis as a manifestation of heart failure, a finding which portends fatal outcome in fetuses with vein of Galen malformation).
3. Fetus with VOGM in whom the straight sinus or falcine sinus draining the prosencephalic varix measures less than 7 mm on fetal MRI (T2-weighted coronal or axial slice, medio-lateral diameter measured at the narrowest point of the sinus along the anterior-posterior axis), fitting fetal MRI criteria for likely evolution into the IT cohort
4. Severe maternal obesity pre-pregnancy as defined by body mass index (BMI) of 40 or greater
5. Fetuses with major extracranial congenital anomalies
6. Evidence of preterm labor, rupture of membranes or abruption
7. Maternal coagulopathy: INR > 1.2; PT/PTT above normal ranges for the lab; platelets <100
8. Any maternal use of anticoagulants, whether prophylactic or therapeutic.
9. Prior maternal medical history that would preclude epidural anesthesia
10. Multi-fetal pregnancy
11. Placenta previa or accreta
12. Participation in another fetal study that influences maternal and fetal morbidity and mortality
13. Known maternal hypersensitivity to 316LM stainless steel
14. Supine hypotensive syndrome