Congenital absence of the inferior vena cava: a rare risk factor for idiopathic deep-vein thrombosis.

Congenital absence of the inferior vena cava (AIVC) is a rare vascular defect, commonly reported as a fortuitous finding. The presence of AIVC in patients with DVT is underestimated because AIVC cannot be detected by compression B-mode ultrasonography. By use of computed tomography, we diagnosed four cases of AIVC in young patients with idiopathic DVT over a 5 year period. Based on the occurrence of DVT in patients below 30 years in our area during the same period, we estimate that AIVC is present in about 5% of cases of DVT in young patients. Computed tomography or angiography should be used for the diagnosis of idiopathic DVT in young patients.