Bilateral thalamic developmental venous variations (DVVs) draining into same internal cerebral vein: a case report and review with emphasis on DVVs with outflow restriction

Developmental venous variations (DVVs) are anatomic variations of normal transmedullary veins which are often discovered incidentally. Although they are accepted as benign compensatory venous drainage systems, they may become symptomatic or clinically significant due to flow-related causes. The fragile venous drainage systems increase vulnerability to in–out flow alterations. Increased inflow or decreased outflow causes rise in venous pressure, which may subsequently produce ischemic symptoms. Obstruction or stenosis of the collector vein is the most common cause of decreased outflow of a DVV. However, in the absence of collecting vein stenosis, venous hypertension may still exist due to volume overload. In case of multiple DVVs with single combined drainage pathway, functional outflow restriction may occur due to diminished capability of the vessel to adapt to pressure changes. In this report, we present a case with bilateral thalamic DVVs, which cause parenchymal amorphous calcification and drain into the left internal cerebral vein. A review of the literature on DVVs with outflow restriction including pathophysiological mechanisms is also discussed.