The inferior venacava conveys blood to the right atrium from all the structures below the diaphragm. It is formed by the union of common iliac veins at fifth lumbar vertebral level. Then it ascends up anterior to the vertebral column, passing through the posterior surface of the liver, pierces the diaphragm and ascends up and reaches the inferoposterior part of the right atrium. It has got 2 parts ---1.Abdominal part 2.Thoracic part

RELATIONS---
Abdominal part
Anteriorly--- Root of mesentry with its vessels, head of pancreas, superior part of duodenum. Above the duodenum it is covered by peritoneum of posterior surface of epiploic foramen. Above this the liver is anterior.
Posteriorly--- Lower three lumbar intervertebral bodies, anterior longitudinal ligament and right psoas major muscle.
Right lateral--- Right ureter, descending part of duodenum, medial border of right kidney and right lobe of liver.
Left lateral--- Aorta and caudate lobe.

Thoracic part---
It is partly outside and partly inside the pericardial sac. The extra pericardial sac is separated from right pleura and lung by right phrenic nerve. The intra pericardial part is covered except posteriorly by inflected serous pericardium.

SURFACE ANATOMY---
It begins just below the transtubercular plane, ends behind the sternal end of sixth right costal cartilage.
Variations---
1. May be placed below the level of renal veins.
2. Complete visceral transposition, inferior venacava is situated left of aorta.

Superficial connections
Epigastric vein, circumflex iliac vein, lateral thoracic vein, thoracoepigastric vein, internal thoracic vein, lumbovertebral anastomotic vein.
Deep connections
Azygos vein, hemiazygos vein and lumbar veins.
Tributaries—
Common iliac vein, lumbar veins, right testicular or ovarian vein, renal vein, right suprarenal vein, inferior phrenic and hepatic veins.

CLINICAL ANATOMY---
1. Thrombosis of veins---
Thrombosis of inferior venacava is usually presented as swelling of either one leg or both legs and back without ascites and increase of temperature. Collateral circulation is soon established by the enlargement of deep and superficial veins.
Deep vein thrombosis is a life threatening condition. Main site of thrombosis is the lower limbs. It is usually unilateral but may be bilateral when they are extensive and extends into pelvis and inferior venacava.

Factors leading to venous thrombosis—
1. Change in the vessel wall with damage to endothelium due to injury or inflammation.
2. Dimnished rate of blood flow in veins, occurs during and after operation and in debilitating conditions like stroke and myocardial infarction.
3. Increased coagulability of blood following surgery in thepresence of infection or systemic malignancy.

Causes of swollen leg—
1. Venous thrombosis.
2. Calf haematoma.
3. Cellulitis.
4. Baker’s cyst rupture.
5. Pelvic disease obstructing lymphatic or venous return.
6. Hypoalbuminaemia

Investigation of venous diseases---
1. Venography.
2. Doppler ultrasound.
3. Photoplethysmography
4. Duplex ultrasound imaging

Management of Deep vein thrombosis---
1. Heparin therapy.
2. Prevent pulmonary embolism.
3. Compression stockings.
4. Avoid prolonged standing.
5. Keep the limbs elevated.

2. Portal hypertension---
Prolonged elevation of portal venous pressure(normal 2-5 mm of Hg) above 12 mm of Hg. Increased portal vascular resistance is the main factor causing portal hypertension.
Causes—
1. Extrahepatic post-sinusoidal --- Budd-Chiari syndrome.
2. Intrahepatic post-sinusoidal --- Venoocclusive disease.
3. Sinusoidal --- Cirrhosis.
4. Intrahepatic presinusoidal --- Sarcidosis, Schistosomiasis.
5. Extrahepatic presinusoidal --- Portal vein thrombosis.
Due to increased portal vascular resistance, there will be development of collateral vessel, bypassing the liver and enters the systemic circulation through the inferior venacava. Main site of collateral vessel formation are at lower end of oesophagus, stomach, rectum, anterior abdominal wall and renal, lumbar, ovarian and testicular vasculature.

Clinical features---
1. Splenomegaly.
2. Hypersplenism.
3. Thrombocytopenia.
4. Caput medusa.
5. Bleeding varices.
6. Fetor hepatis.

3. Thrombophilia---
Condition in which severe deficiency of antithrombin III, protein C and protein S leads to episodes of venous thrombosis.

4. Pulmonary embolism---
Fatal complication of lower limb deep vein thrombosis. Aclot from the lower limb vein detached from its site and passes via the inferior venacava and right heart to pulmonary arteries.

REFERENCES
1.Clinically oriented anatomy by Keith.L.Moore. 2. Gray’s anatomy.
3.Grant’s method of anatomy 4. Davidson’s principles and practice of medicine.