Case Presentation: A 45 years old Vietnamese male was diagnosed with left leg deep vein thrombosis about 2 years ago in Vietnam for which he was taking herbal supplements without improvement. Soon after immigrating to the United States six months ago, he was urgently admitted to hospital for an episode of bilateral leg swelling and pain, left greater than right and diagnosed with DVT. CT abdomen and pelvis revealed congenital atresia of inferior vena cava and of the bilateral common iliac veins, resulting in multiple venous collaterals in the abdomen, retroperitoneum and subcutaneous tissue. IVC atresia was believed to be strongly associated with deep vein thrombosis in our patient. He had been a lifelong nonsmoker and did not have family history of thrombotic disorders. Workup for hypercoagulable disorders including Factor V Leiden mutation, Prothrombin gene mutation, Anticardiolipin antibody panel, and antithrombin 3 activity were all unremarkable. Subcutaneous weight based enoxaparin and warfarin overlap for anticoagulation was initiated with plan for lifelong therapy. As his work schedule precluded him to obtain regular INR checks, he was recently switched to novel anticoagulant Rivaroxaban. Unfortunately, he failed treatment with Rivaroxaban and presented back to our hospital with worsening left lower extremity pain and swelling. On exam, left leg was swollen, erythematous and had superficial ulcerations. Doppler ultrasound showed extensive thrombosis in left common femoral vein, proximal femoral vein, proximal profundal vein, and popliteal vein. Acute superficial thrombophlebitis was found in the left great saphenous vein at the proximal calf and in a branch at the left proximal calf. He was evaluated by vascular surgery and hematology teams. No surgical intervention was warranted. He was restarted on overlap regimen of enoxaparin and warfarin. As leg swelling and pain improved, he was discharged home in good condition.

Discussion: Inferior Vena Cava atresia is a rare vascular anomaly with an estimated prevalence of 1% in general population. At 4-6 weeks of gestation, regression and fusion of three sets of paired veins- posterior cardinal, subcardinal, and supracardinal veins forms IVC. Failure of these paired veins to fuse results in IVC anomaly. Patients with IVC atresia develop robust collateral deep venous system with or without azygous and hemizygous continuation in the IVC. During physical exertion these collaterals inadequately drain the lower limbs, thus causing venous stasis, superficial ulcerations and deep vein thrombosis (DVT). In young patients with unexplained DVTs, recurrent lower extremity ulcers, and enlarged abdominal veins, IVC atresia should be considered as a differential diagnosis. It is estimated that congenital anomalies of the IVC cause approximately 5% of cases of DVT in patients less than 30 years old. CT angiography is the best study to diagnose IVC anomalies. Lifelong anticoagulation may be necessary as there remains irreversible risk of thrombosis.

Conclusions: IVC atresia was believed to be the culprit for recurrent deep vein thrombosis in our patient. Clinicians should consider IVC anomalies as a possible cause in young patients with unexplained, extensive and bilateral deep vein thrombosis. There are no standard guidelines about treatment of DVT related to IVC atresia but life long anticoagulation may be necessary in these patients given the nature of the anomaly.