We present a case of vein of Galen aneurysmal malformation in an adult, the rupture of which caused a fatal hemorrhage. Macroscopic examination, together with plastination of specimen with S10, and microscopic examination showed connection of the aneurysm with the right thalamoperforating artery and, bilaterally, with the posterior choroidal and mesencephalic arteries. Histology also showed thinning of the aneurysmal wall, due to marked reduction of the muscular media at the point of rupture, and its connection with an arteriovenous malformation of the left thalamus. A review of the anatomy of the Galenic system shows that the medullary veins curve at an acute angle to form the paired internal cerebral veins, with a sudden change in flow and that, from late fetal life, the vein of Galen curves around the splenium to enter the straight sinus at an angle opposing its flow. Based on anatomical study and a review of the literature, we suggest that aneurysmatic dilatation of the vein of Galen may result from a combination of pathological and predisposing anatomical factors. The anatomical characteristics of the origin of the internal cerebral veins and of the entry of the vein of Galen into the straight sinus make particularly susceptible to the hemodynamic effects of arteriovenous shunts the vein of Galen itself, which is situated in the cisterna ambiens, an anatomical space that does not impede its enlargement.