PO066 | ONE IN TWO MILLION: A 'DOUBLE-HIT' CASE OF INFRARENAL VENA CAVA AGENESIS AND TRIPLE-POSITIVE ANTIPHOSPHOLIPID SYNDROME

N. Portesi, S. Pontoglio, G. Martini | ASST Spedali Civili di Brescia, Italy

Background. Inferior vena cava (IVC) agenesis is a rare congenital vascular anomaly, with an estimated prevalence of 0.0005%–1% in the general population. Although frequently asymptomatic, it leads to extensive collateral circulation to compensate for impaired venous return. This chronic blood stasis is a critical anatomical risk factor for deep vein thrombosis (DVT), accounting for up to 5% of idiopathic events in young adults. Antiphospholipid Syndrome (APS) is a systemic autoimmune disease characterized by persistent antiphospholipid antibodies (aPL) associated with thrombosis; its prevalence is estimated at 40-50 cases per 100,000 persons with annual incidence of 1-2 cases per 100,000. Within this spectrum, the even rarer triple-positive phenotype (LAC, anti-cardiolipin, and anti-β2-glycoprotein I) stands out as a potent biochemical driver of thrombosis, carrying the highest risk for recurrence.
Case report. A 33 years old male presented with a massive first DVT involving bilateral femoral veins and the left iliac and popliteal veins. Initial management was challenging; the patient exhibited poor response to therapeutic low-molecular-weight heparin. Clinical stabilization was achieved only after initiating Vitamin K Antagonists (VKA) within the therapeutic INR range (2.0–3.0). Despite optimal treatment, complete recanalization was never achieved. After three years of stable anticoagulation, the patient self-discontinued VKA and suffered a symptomatic recurrence within 24 hours: a superficial vein thrombosis of the right great saphenous vein extending to the saphenofemoral junction. Thrombophilic screening confirmed a high-risk triple-positive APS profile. Simultaneously, a vascular study documented an extensive compensatory network with anomalous anastomoses (apparently arterial-venous). Subsequent abdominal contrast-enhanced CT provided the definitive anatomical explanation: agenesis of the infrarenal IVC and common iliac veins, with prominent collateral circulation involving the superficial system, hypogastric veins, pelvic varicocele, and presacral drainage. Lifelong anticoagulation was indicated. In 2015, the patient was enrolled in the TRAPS study and randomized to the warfarin arm. He has since been maintained on VKA therapy, supplemented by hydroxychloroquine and low-dose aspirin following episodes of amaurosis fugax and the incidental finding of an IgM-kappa monoclonal gammopathy of undetermined significance. Currently, 17 years after the first episode, the patient remains in good clinical standing with good adherence (Time in Therapeutic Range: 90%).
Conclusions. The simultaneous occurrence of infrarenal IVC agenesis and triple-positive APS is an exceptionally rare "double-hit" model of venous thrombosis, estimated to affect fewer than one in two million individuals. This case highlights how a permanent anatomical anomaly inducing chronic stasis can act as a critical trigger in the presence of a potent autoimmune prothrombotic state. The immediate recurrence upon VKA withdrawal underscores the extreme hypercoagulability of this phenotype, which requires an extended multidisciplinary approach to ensure long-term clinical stability.