Teaching Case

Seizures, macrocephaly, heart failure

The patient was referred with seizures, developmental delay, and macrocephaly. Clinical examination revealed signs and symptoms of increased intracranial pressure and heart failure. MR imaging and MR angiography studies were performed on a 1.5 Tesla unit.

Aneurysmal dilatation of the vein of Galen occurs when the nidus of a parenchymal arteriovenous malformation, which usually is located in the thalamus or midbrain, drains into the true vein of Galen. On the other hand, recent embryologic studies suggested that the dilated venous structures at the same location, which receive direct arteriovenous fistulas, actually represent the persistent, primitive prosencephalic vein of Markowski. This persistent fetal structure does not communicate with the deep venous system, and its usual outflow is to the falcine or straight sinus. Some authors believe that there is an associated intrauterine occlusion (i.e. thrombosis) of some of the dural sinuses with or without subsequent recanalization or the sinuses can show total or partial absence, usually referred to as venous outflow restriction. This reflects a causal relationship. Herein, we intentionally use the term "aneurysm of the persistent, primitive prosencephalic vein of Markowski" instead of the generally used term "vein of Galen malformation", in order to emphasize the embryologic difference. Aneurysms of the persistent, primitive prosencephalic vein of Markowski have two types with respect to angioarchitectural analysis: the choroidal type, and the mural type. The choroidal type is more common, and consists of a plethora of small vessels from pericallosal, choroidal, and thalamoperforator arteries forming direct arteriovenous fistulas in the anterior wall of the prosencephalic vein. The mural type, however, is less common, and there are a few (usually one to four), and larger-sized arteries which form the direct arteriovenous fistula or fistulas with the prosencephalic vein. Our patient represents the mural type of the anomaly. On the other hand, development of spontaneous thrombosis is rare in such malformations. In case of spontaneous thrombosis, the usual flow-void or turbulent flow will not be seen on MRI. In the current patient, thrombosis occured in such a homogenous fashion that it was overlooked during the initial interpretation. It should be noted that in case of spontaneous thrombosis of such a malformation, evolution of the condition should be monitored, and treatment delayed.