Inferior vena cava agenesia and a massive bilateral iliofemoral venous thrombosis.

The absence of the inferior vena cava is a rare congenital anomaly and represents a modest risk for deep-venous thrombosis. When associated with genetic polymorphism or other hypercoagulable states, the risk can increase several times. A case of young man with the inferior vena cava agenesia and deep-venous thrombosis of both legs triggered by the physical effort is reported. The view that the congenital inferior vena cava malformation represents a predisposition to deep-venous thrombosis in spite of well-developed collateral circulation is supported. In these circumstances, various external triggers (physical effort, hormonal contraception etc) may precipitate thrombosis. Because the patient had no other convincing and permanent risk factors for thrombosis, the lifelong anticoagulant therapy was not recommended.