vena cava

The superior vena cava is formed by the union of the right and left brachiocephalic veins and drains into the right atrium. It has no valves and lies in the middle mediastinum. SVC syndrome occurs when there is obstruction (often due to bronchogenic carcinoma, lymphoma, or thrombosis from central lines) leading to facial plethora, distended neck and upper extremity veins, edema of the face/arms, and headache due to increased intracranial pressure—a medical emergency requiring prompt diagnosis.

The inferior vena cava is formed by the union of the common iliac veins (at L5) and ascends retroperitoneally, passing through the caval hiatus of the diaphragm at T8 to enter the right atrium. It receives blood from the hepatic veins, renal veins, gonadal vein (right only; left gonadal vein drains into left renal vein), and lumbar veins. IVC filters may be placed to prevent pulmonary embolism in patients with DVT who cannot receive anticoagulation. IVC thrombosis can occur with hypercoagulable states, renal cell carcinoma (which has a propensity to invade the IVC), or compression by tumors/pregnancy (causing IVC compression syndrome in pregnant patients supine, leading to hypotension).

Developmentally, the IVC forms from a complex fusion of three paired embryonic veins (subcardinal, supracardinal, and posterior cardinal veins), explaining the various anatomic variants like double IVC or left-sided IVC seen on imaging.

Clinically, understanding vena cava anatomy is essential for central line placement, IVC filter placement, and interpreting IVC collapsibility on ultrasound as a marker of volume status/right atrial pressure.