Abstract
Absence of the infrarenal segment of the inferior vena cava is an extremely rare anomaly. The reasons for such a developmental failure are unclear. Most researchers believe that the cause lies in embryonic dysgenesis affecting separate segments or the entire inferior vena cava. Others suggest that absence of the inferior vena cava is not embryonic in origin, rather the result of intrauterine or perinatal thrombosis. We report a case here that during a period of six months, inferior vena cava first occluded, then become redundant in a baby girl with several chromosomal and gene defects, including Down syndrome and hereditary thrombophilia, admitted to our hospital due to the swelling and redness of the right lower extremity. From this observation, we propose that the absence of the inferior vena cave was not of embryonic origin but due to thrombosis.