Azygos continuation of the inferior vena cava

Azygos continuation of the inferior vena cava (also known as absence of the hepatic segment of the IVC with azygos continuation) is an uncommon vascular anomaly, with prevalence about 0.2%–3%¹, and is a cause of a dilated azygos vein. 

As the name suggests, the hepatic segment of the IVC is absent and the hepatic veins join and drain directly into the right atrium. 

A common associated abnormality is duplication of inferior vena cava (IVC). On these cases, usually the left IVC typically ends at the left renal vein which crosses anterior to the aorta to join the right IVC. Then the right IVC remains as the azygos vein, missing the liver. The azygos vein joins the superior vena cava (SVC) at the normal location in the right paratracheal space.

Other arrangements in the duplicated inferior vena cava drainage can be found, such as:

• Double IVC with retroaortic right renal rein and hemiazygos continuation of the IVC;
• Double IVC with azygos and hemiazygos continuation of each duplicated IVC. 

Clinical presentation

In most cases it is found incidentally in asymptomatic patients. An association with  congenital heart disease and asplenia or polysplenia syndromes has been reported. 

It is important to recognize the enlarged azygos vein at the confluence with the superior vena cava and in the retrocrural space to avoid misdiagnosis as a right-sided paratracheal mass or retrocrural adenopathy.

Preoperative knowledge of the anatomy may be important in planning cardiopulmonary bypass and to avoid difficulties in catheterizing the heart.

Radiographic features

Plain film

On frontal chest x-ray the mediastinum is widened and the azygos arch enlarged. 

CT and MRI

Cross sectional imaging usually has no difficulty in identifying the abnormality, demonstrating the anatomy elegantly (see above). 

Treatment and prognosis

As an isolated finding, azygos continuation of the IVC requires no treatment. 

Preoperative knowledge of the anatomy may be important in planning cardiopulmonary bypass and to avoid difficulties in catheterizing the heart.