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The inferior vena cava (IVC) is a large retroperitoneal vessel formed by the confluence of the right and left common iliac veins. Anatomically this usually occurs at the L5 vertebral level. The IVC lies along the right anterolateral aspect of the vertebral column and passes through the central tendon of the diaphragm around the T8 vertebral level. The IVC is a large blood vessel responsible for transporting deoxygenated blood from the lower extremities and abdomen back to the right atrium of the heart. It has the largest diameter of the venous system and is a thin-walled vessel. These anatomic characteristics make it ideal for transporting large quantities of venous blood. Many veins contain one-way valves to ensure the forward flow of blood back toward the heart. The IVC, however, does not contain such valves, and forward flow to the heart is driven by the differential pressure created by normal respiration. As the diaphragm contracts and creates negative pressure in the chest for the lungs to fill with air, this pressure gradient pulls the venous blood from the abdominal IVC into the thoracic IVC and subsequently into the right heart. The IVC enters the right atrium of the heart after coursing through the diaphragm, entering the posterior inferior aspect of the atrium. The IVC enters the right atrium inferior to the entrance of the superior vena cava (SVC). The IVC is a mostly symmetric vessel with a few exceptions. Due to the IVC residing on the right side of the vertebral column the vessels entering the IVC from the left side of the body, like the left renal vein, are longer than their anatomic counterparts on the right. Other left-sided veins, like the left adrenal and left gonadal vein, first join the left renal vein before joining the IVC and continuing as venous flow returning to the heart. This differs from the right side of the body where the right adrenal and right gonadal vein directly join the IVC without first joining the right renal vein. Anatomic variants venous of anatomy involving both right and left sides have been described.[1]

The IVC is a mostly symmetric vessel with a few exceptions. Due to the IVC residing on the right side of the vertebral column the vessels entering the IVC from the left side of the body, like the left renal vein, are longer than their anatomic counterparts on the right. Other left-sided veins, like the left adrenal and left gonadal vein, first join the left renal vein before joining the IVC and continuing as venous flow returning to the heart. This differs from the right side of the body where the right adrenal and right gonadal vein directly join the IVC without first joining the right renal vein. Anatomic variants venous of anatomy involving both right and left sides have been described.[1] Blood from the left and right femoral veins enters the IVC via the left and right common iliac veins, respectively. Blood from the abdominal viscera travels into the portal vein and enters the IVC via the hepatic veins after traversing the liver and its sinusoids. Venous blood from the abdominal wall reaches the IVC through lumbar veins. Ascending lumbar veins connect lumbar veins to the azygos vein and this provides some collateral circulation between the inferior vena cava and the superior vena cava.[2] This potential for a collateral flow could be critical if either of the larger veins becomes obstructed. Below is a list of (most common) vertebral levels at which different veins enter the IVC. T8: Hepatic veins, inferior phrenic veins L1: Right suprarenal vein, renal veins L2: Right gonadal vein L1-L5: Lumbar vertebral veins L5: Right and left common iliac veins