Two cases of aneurysmal malformations of the vein of Galen (AVG) with spontaneous thrombosis are reported. Angiogram and MRI before thrombosis demonstrated AVGs with slow arteriovenous shunts and associated stagnation of contrast in the venous sac secondary to severe outflow restriction. Based on these findings, one patient was managed conservatively, and the other underwent placement of a ventriculoperitoneal shunt. Surveillance of the lesions with subsequent MRIs revealed spontaneous thrombosis of the AVGs with excellent clinical outcomes. Proposed mechanisms of spontaneous thrombosis include slow flow shunts, obstruction of the venous outflow or obstruction of the feeding artery. Similar cases in the literature are reviewed with special emphasis on diagnostic tests, symptomatology, mechanisms of thrombosis and therapeutic options.