Vein of Galen aneurysm is a rare formof arteriovenous malformation in which the embryonic precursor to the vein of Galen, a vein at the base of the brain, dilates causing too much blood to rush to the heart. This can lead to rapid heart failure. Other features may include increased head circumference resulting from hydrocephalus, unusually prominent veins on the face and scalp, developmental delay, persistent headache, and other neurological findings. Vein of Galen aneurysm is often recognized on an ultrasound late in pregnancy. In other cases, it is diagnosed after birth. Although the exact cause remains unknown, this condition appears to result from a defect in early fetal development. Treatment is aimed at decreasing the blood flow through the malformation while maximizing the blood supply to the brain. Minimally invasive surgical techniques are preferred, such as endovascular embolization. The disease is Monarch Disease Ontology identifier MONDO_0015196 (vein of Galen aneurysm). Also known as: vein of Galen arteriovenous malformations.