Case 6
History:
28 year old female with unexpected abnormality seen on a routine chest radiograph.
Findings:
Frontal chest radiograph showing unusual prominence of the upper right medistanium suggestive of enlarged nodes. An enhanced CT scan of the chest shows a dilated azygous vein with absent intrahepatic portion of the inferior vena cava.
Diagnosis:
Azygos and hemiazygos continuation of the IVC
Discussion:
The azygos system is a paired paravertebral venous pathway in the posterior thorax. The azygos vein originates at the junction of the right ascending lumbar and subcostal veins, enters the chest through the aortic hiatus, and ascends along the anterolateral surface of the thoracic vertebrae At T5-T6. It arches ventrally just cephalad to the right main bronchus and drains into the SVC. Similar to the azygos vein, the hemiazygos vein originates at the junction of the left ascending lumbar and left subcostal veins and often receives tributaries from the left renal vein and inferior vena cava (IVC).
These anomalies may be isolated or associated with other anomalies. The incidence in patients with congenital heart disease undergoing cardiac catheterization ranges from 0.2 – 1.3 percent. Azygos continuation is common in patients with polysplenia (left isomerism) but rare in patients with asplenia (right isomerism). Other associated anomalies include abnormal abdominal situs and a left or duplicated IVC. The imaging features of azygos continuation of the IVC include dilatation of the azygos vein, azygos arch and SVC caused by increased flow. The hepatic veins drain into the right atrium via the suprahepatic IVC. The hepatic segment of the IVC is absent or hypoplastic, and this condition must be documented to exclude other causes of an enlarged azygos vein. Azygos continuation has also been reported in association with an azygos lobe.
