Delayed diagnosis of congenital inferior vena cava agenesis presenting as post-thrombotic syndrome: a case report

Abstract Introduction Congenital anomalies of the inferior vena cava (IVC) are rare and may remain clinically unrecognized for years. Inferior vena cava agenesis or aplasia is most commonly identified in younger patients presenting with unprovoked deep vein thrombosis (DVT), often after delayed or incomplete diagnostic evaluation. Case report We report a 37-year-old man admitted for evaluation of post-thrombotic syndrome with a history of bilateral unprovoked lower-extremity DVT diagnosed five years earlier. Previous anticoagulant therapy had been administered for two years. Laboratory evaluation, including thrombophilia screening, autoimmune testing, and oncological workup, showed no clinically significant abnormalities. Compression Doppler ultrasound demonstrated chronic bilateral venous thrombosis with partial recanalization. Contrast-enhanced CT of the abdomen and pelvis initially suggested inferior vena cava thrombosis with extensive collateral circulation. However, further radiological reassessment and thoracic CT demonstrated complete absence of the inferior vena cava with prominent azygos and hemiazygos collateral drainage, consistent with congenital IVC agenesis. Long-term anticoagulation with apixaban and compression therapy were initiated. Conclusion Congenital absence of the inferior vena cava should be considered in younger patients with unprovoked or recurrent DVT, particularly in the absence of identifiable thrombophilic conditions. This case illustrates how easily the diagnosis may be overlooked and emphasizes the importance of clinical suspicion, comprehensive imaging, and multidisciplinary evaluation in patients with atypical thrombotic disease.