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Findings:Chest X-Ray: There is an abnormal convex soft tissue density in
the region of the azygous vein.
MRI: The azygous vein is dilated. There is absence of the
intrahepatic portion of the IVC with the infrarenal IVC
continuing into the thorax via the azygous vein. The
hepatic veins drain directly into the base of the right atrium.
Diagnosis: Interrupted IVC with azygous continuation.
Discussion: The IVC is formed by the junction of the two common iliac veins at the L5 level. It ascends to the right of midline within the abdomen to terminate at the posterior-inferior aspect of the right atrium within the thorax. The average IVC diameter is 2.5 cm and is valveless except for a rudimentary valve, the eustachius valve, at its junction with the right atrium. Tributaries include the ascending lumbar, renal, adrenal, gonadal, inferior phrenic, and hepatic veins.
The retroperitoneal venous system develops embryologically from three paired venous fetal veins. The posterior cardinal veins, which do not contribute to the formation of the IVC, the subcardinal veins, which from the prerenal IVC and the supracardinal veins, which form the postrenal IVC, as well as contributing to the formation of the azygous and hemiazygous veins. Absence of the intrahepatic portion of the IVC results from failure of the right subcardinal vein to anastomose with the hepatic veins.
Other congenital anomalies of the vena cava include a duplicated IVC and left-sided IVC. Duplication of the IVC results from persistence of the right and left supracardinal veins and has a 2- 3% incidence in the general population. The paired IVCs typically join at the level of the renal veins. Left-sided IVC is rate, occurring in approximately 0.5% of the population, and is a result of persistence of the supracardinal vein (rather than the right). The left IVC joins the left renal vein, which subsequently crosses the midline to join with the normal right- sided suprarenal IVC.
References:
Johnsrude IS et al: A practical approach to angiography, Boston,
1987, Little Brown.
Kadir S: Atlas of normal and variant angiographic anatomy,
Philadelphia, 1991, WB Saunders.
Sonin AH, Mazer MJ, Powers TA: Obstruction of the Inferior Vena
Cava: A Multimodality Demonstration of causes, Manifestations,
and Collateral Pathways, Radiographics, 12: 309-322, 1992.
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