Inferior vena cava
The inferior vena cava has a longer course than the aorta in the abdomen. It begins opposite L5 vertebra by the confluence of the two common iliac veins behind the right common iliac artery (Fig. 5.42A). It runs upwards on the right of the aorta, grooves the bare area of the liver, and pierces the central tendon of the diaphragm on a level with the body of T8 vertebra. It lies on the bodies of the lumbar vertebrae and the right crus of the diaphragm, overlapping the right sympathetic trunk, and crossing the right renal, suprarenal and inferior phrenic arteries (Fig. 5.43). It also partly overlaps the right suprarenal gland and the coeliac ganglion. In the infracolic compartment the inferior vena cava lies
behind the peritoneum of the posterior abdominal wall; it is crossed by the root of the mesentery, the right gonadal artery and the third part of the duodenum. In the supracolic compartment it lies at first behind the portal vein, head of the pancreas and bile duct, then behind the peritoneum that forms the posterior wall of the epiploic foramen. Above this it is behind the bare area of the liver, into which it excavates a deep groove (Fig. 5.32B). With the exception of the gonadal (especially testicular)
veins, the inferior vena cava and its tributaries do not have valves. The surface marking of the inferior vena cava is a vertical
line 2.5 cm to the right of the midline from the intertubercular plane to the sixth costal cartilage.
Tributaries
The vena caval tributaries are not identical with the branches of the abdominal aorta. In particular there is none corresponding to the three ventral branches to the gut. The blood from the alimentary tract, pancreas and spleen is collected by the portal venous system, and only after passing through the liver does it reach the vena cava via the hepatic veins, the vena cava’s highest tributaries. Above its formation by the union of the two common iliac veins, the other tributaries (in ascending order) are the fourth and third lumbar veins of both sides, right gonadal, both renal, right suprarenal and both inferior phrenic veins. Each common iliac vein is formed in front of the sacroiliac joint by the union of the internal iliac vein from the pelvis (see p. 309) and the external iliac vein, the continuation of the femoral vein, which enters the abdomen on the medial side of its corresponding artery and runs along the pelvic brim. The two common iliac veins continue upwards to unite to form the vena cava behind the right common iliac artery (Fig. 5.42A). Because the vena cava is to the right of the midline, the left common iliac vein is longer than the right. It is posteromedial to its artery and joins its fellow almost at a right angle after bulging forwards across the body of L5 vertebra. It may be compressed by the overlying artery. The right common iliac vein is almost vertical and lies posterior and then lateral to its artery. Each common iliac vein receives iliolumbar and perhaps lateral sacral veins, while the left usually receives the median sacral vein which lies on the right of the corresponding artery. The lumbar veins accompany the lumbar arteries and
drain the lateral and posterior abdominal walls, with anastomotic connections anteriorly with the epigastric veins and posteriorly with the vertebral venous plexuses. The fourth and third empty into the vena cava; those from the left pass behind the aorta, and all are expected to lie behind the sympathetic trunks but occasionally one or more may be in front. The second and first do not usually reach the vena cava but join the ascending lumbar vein, which connects common iliac, iliolumbar and lumbar veins and passes vertically upwards behind psoas and in front of the lumbar transverse processes. Each ascending lumbar vein joins the subcostal vein to form the azygos (on the right) and hemiazygos (on the left) veins respectively (see p. 211). These veins enter the thorax, on the right through the aortic opening of the diaphragm, and on the left by perforating the left crus. The gonadal veins accompany the arteries (testicular
or ovarian) and each is usually paired. As they run up on psoas the two venae comitantes unite. On the right the vein usually enters the vena cava just below the renal vein at an acute angle; but the right testicular vein may occasionally join the renal vein. The left gonadal vein invariably joins the left renal vein at a right angle.
Abdomen
The testicular veins usually have valves at their terminations; they may be present in the ovarian veins. The renal veins lie in front of the renal arteries and
behind the pancreas, and join the vena cava at right angles, at the level of L2 vertebra (Fig. 5.44). Each emerges from the hilum of the kidney as five or six tributaries which soon unite. The left renal vein is three times as long as the right (7.5 cm compared with 2.5 cm) and usually crosses in front of the aorta. It receives the left suprarenal
vein and left gonadal vein and possibly a left inferior phrenic vein. In contrast the shorter right renal vein usually drains only its own kidney. The left renal vein may have to be ligated and divided
during surgery for aortic aneurysm. Provided that this is done to the right of the point of entry of the gonadal and suprarenal veins the kidney is not harmed. Rarely, the left renal vein may be double, with one vein passing anterior and one posterior to the aorta, or only a posterior vein may be present. While the left suprarenal vein runs downwards and medially to the left renal vein, the right suprarenal vein is a very short vessel that passes horizontally to the posterior aspect of the inferior vena cava behind the bare area of the liver (Fig. 5.43)—an arrangement that complicates the surgery of the right gland. The inferior phrenic veins accompany the arteries on
the lower surface of the diaphragm and normally join the vena cava just below the liver, but the left vessel may join the left renal or suprarenal vein, or even be double with different destinations. The three main hepatic veins (right, central and left)
and several accessory hepatic veins enter the vena cava as it lies in its groove on the back of the liver; they are further described on page 262.
A B
Figure 5.44 CT scans of the upper abdomen (viewed by convention from below). In A, the left renal vein crosses in front of the aorta to enter the inferior vena cava. The right crus of the diaphragm is seen beside the aorta. In B, the pelvis of the right kidney is indicated by the white opacity (representing oral contrast medium which has been absorbed and excreted by the kidney), while on the left side the ureter, similarly outlined, lies immediately medial to the lower pole of the kidney. The psoas major and quadratus lumborum muscles are seen on either side of the lumbar vertebra.