Congenital agenesis of inferior vena cava: a rare cause of unprovoked deep venous thrombosis.

Congenital anomalies of the inferior vena cava (IVC), although rare, are a risk factor for lower limb deep venous thrombosis (DVT). A 19-year-old male presented with a left flank and groin pain caused by iliofemoral venous thrombosis. Vascular imaging by computed tomography (CT) scanning and venography demonstrated agenesis of the IVC. Catheter-directed thrombolysis via a popliteal vein was attempted but did not alter the patency of the common femoral vein outflow collaterals into the retroperitoneal azygous venous system. The patient was anticoagulated using systemic heparin infusion and clinical symptoms resolved within 5 days. He was transitioned to oral Coumadin anticoagulation, and follow-up venous duplex testing demonstrated no infrainguinal DVT and phasic venous flow with respiration in the femoral vein indicating patent collateral veins. Anomalies of the IVC are present in 0.3-0.5% of otherwise healthy individuals. Agenesis of the IVC has an incidence of 0.0005-1% in the general population but is found in almost 5% of patients <30 years of age with unprovoked lower limb DVT. In adults, IVC agenesis anomaly can cause diagnostic problems in the paravertebral area because of the tumor-like appearance of the azygous venous collaterals on noncontrast CT imaging. In young adults presenting with unprovoked lower limb DVT, the presence of an IVC anomaly should be considered and evaluated for by venous duplex testing and if necessary CT venography.