Collateral pathways in Budd-Chiari syndrome: CT and venographic correlation.

B udd-Chiari syndrome (BCS) is a diverse group of conditions associated with obstruction of hepatic venous outflow at the level of the large hepatic vein or the extrahepatic segment of the inferior vena cava (IVC). BCS is classified as primary or secondary, depending on the cause and pathophysiologic manifestations. Although BCS in Western countries is most often due to thrombotic obstruction of the hepatic vein or IVC caused by systemic disease or malignant tumors, primary membranous or segmental obstruction of the IVC is the most common cause of BCS in Asian countries ( 1. 21. Because primary BCS is chronic. several pathways of collateral vessels commonly develop. Development of collateral circulation is contingent on the level of obstruction and the length of the obstructed segment. Collateral pathways of upper caval obstruction have not been as carefully studied as other areas; findings have mostly relied on venography. Although Cf scans are the most common primary method for evaluating abdominal abnormalities, several CT studies of BCS have dealt largely with changes in liver parenchyma. With knowledge of vascular anatomy on abdominal CT, it is relatively easy to outline the collateral vessels because of their larger caliber due to vascular engorgement [3]. The purpose of this essay is to classify and illustrate the collateral pathways of BCS in abdominal CT scans. Left Renal-Hemiazygos Pathway Anatomically. the left renal vein is more complex than the right because of multiple vessels (the inferior phrenic. capsular. adrenal. and gonadal veins) that join the left renal vein. In addition, the left renal vein communicates with the retroperitoneal vein (by the lumbar. ascending lumbar, and hemiazygos veins) in two thirds of cases 141In fact, the left renalhemiazygos route may constitute the main central pathway. although infrequently (Fig. I ). On Cf scans, such communication may be mistaken for a paraaortic mass.