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SEVERAL PROBLEMS associated with caval interruptionprocedures are related to the anatomy of the infrarenal vena cava and its tributaries. Among these are the site of election for caval interruption, hemorrhage from unsuspected lumbar veins, difficulty in recognition of various levels of the cava in the liiiiited confines of the retroperitoneal approach, and proximal thrombosis with recurrent pulmonary embolism.The literature yields limited pertinent information. Most texts are replete with descriptions of the cava itself, but reference to its lumbar venous tributaries is usually vague and not detailed. Goss' Gray's Anatomy6 gives the impression that there are four pairs of segmental lumbar veins, but there is no description of how many actually enter the cava and the location of their orifices. Similarly there is little information concerning distance between major caval tributaries which is helpful in surgical orientation. The most explicit studies were done by Davis, Milloy, Anson, and associatesl' 2, 4 7 but these are not oriented specifically toward our objectives.One hundred necropsy dissections of the adult infrarenal vena cava and its tributaries were performed to elucidate these problems by determining distances between the major branches and documenting more precisely the number and location of lumbar veins entering the cava, the valves and tributaries of the iliofemoral segments, and anomalies. MethodDissections were performed at necropsy on 100 patients between the ages of 17 and 84 of whom 49 were males and 34 females. Sex was not recorded in the 17 original pa- After routine evisceration bilateral extensions of the autopsy incision were made into each femoral region.The vena cava was transected just below the liver well above the left renal vein. The cava and renal veins were then pinned to the vertebral column to avoid changes in their relationships after dissection. The renal vessels were transected at the kidneys and the kidneys and ureters were removed. The external iliac arteries were ligated and divided midway between the internal iliac arteries and the inguinal ligaments, the internal iliac arteries were ligated and divided, and the iliac arteries and aorta were removed leaving the infrarenal cava-iliofemoral system exposed.The following distances were measured as shown in Figure 1: from the right renal vein to the entrance of the right gonadal vein into the cava and to the caval bifurcation; and from the caval bifurcation to the intemal iliac, greater saphenous and profunda femoris veins.The inferior vena cava and its iliofemoral tributaries were opened in Y-fashion in the midline anteriorly from a point about 2 cm. above the left renal vein to a point approximately 2 cm. below the junction of the superficial and deep femoral veins.The orifices of the lumbar veins were identified, their distances from the lower border of the right renal vein were measured, and their locations were charted on a work diagram. The direction of the lumbar veins was studied in 65 patients. 740

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