Variations in the Basal Vein. A, The most common pattern of venous drainage is posterior (46%). The anterior and deep MCVs join to form the striate segment of the basal vein, which receives the drainage of the anterior and deep middle cerebral and striate veins. The peduncular vein marks the transition between the striate and anterior peduncular segments, and the inferior ventricular vein marks the transition between the anterior and posterior peduncular segments. The anterior peduncular segment connects the striate with the posterior peduncular segment and is also called the anterior basal anastomotic vein, which is well developed in this case. The anterior hippocampal vein runs in the uncal sulcus, and the anterior longitudinal hippocampal vein runs in the fimbriodentate sulcus. They are both tributaries of the inferior ventricular vein or the basal vein at the junction of the anterior and posterior peduncular segments. At the level of the lateral mesencephalic vein, the basal vein continues along the posterolateral midbrain as the proximal mesencephalic segment and receives the pulvinar veins. The distal mesencephalic segment travels posterior to the level of the colliculi in the quadrigeminal cistern, may receive the lateral atrial and anterior calcarine veins, and drains into the vein of Galen. The proximal mesencephalic segment connects the posterior peduncular segment with the distal mesencephalic segment, and is also called the posterior basal anastomotic vein, which is well developed in this case. B, The most common variation of the basal vein is a combination of anterior and posterior venous drainage (32%). In this case, the anterior peduncular segment (anterior anastomotic vein) is rudimentary, and, therefore, the striate segment, including the peduncular, striate, anterior cerebral, and deep middle cerebral veins, drains anteriorly through the preuncal vein into the sphenoparietal sinus or, less commonly, into the cavernous or tentorial sinuses. The inferior ventricular vein and the posterior peduncular and mesencephalic segments drain posteriorly into the vein of Galen. C, Another common variation of the basal vein is a combination of inferior and posterior drainage (13%). In this case, there is a well-developed anterior basal anastomotic vein (anterior peduncular segment) but a rudimentary mesencephalic segment (posterior anastomotic vein). As a consequence, the striate and peduncular segments drain inferiorly through a prominent lateral mesencephalic vein into the superior petrosal sinus. The lateral atrial and anterior calcarine tributaries of the distal mesencephalic segment drain directly into the vein of Galen or internal cerebral veins. (Images courtesy of AL Rhoton, Jr.)