Congenital atresia of the inferior vena cava and antithrombin III deficiency in a young adult: compounding risk factors for deep vein thrombosis.

Atresia, or absence, of the inferior vena cava (AIVC) is a rare, usually fortuitous finding on advanced imaging that predisposes patients to deep venous thrombosis (DVT). In young adults who lack predisposing risk factors but nonetheless develop extensive or bilateral DVTs, AIVC should be considered. We describe a case of a previously healthy 17-year-old male patient who developed an extensive renal vein thrombus due to the absence of the superior portion of his IVC compounded with previously undiagnosed antithrombin III deficiency. We discuss the diagnosis and management of this complicated condition.