Abstract
Extensive iliocaval thrombosis is a rare manifestation of venous thromboembolism and should prompt evaluation for inherited thrombophilia in young patients. We report a previously healthy 21-year-old man with a homozygous factor V Leiden mutation who presented with bilateral groin pain, fever, and syncope two weeks after a 12-hour international flight. Imaging demonstrated extensive thrombosis involving the infrarenal and intrahepatic inferior vena cava, the bilateral common and external iliac veins, and the right renal vein with extensive collateralization. He underwent staged mechanical thrombectomy and balloon venoplasty, followed by indefinite anticoagulation. This case highlights the importance of recognizing atypical presentations of extensive iliocaval thrombosis, the synergistic risk of homozygous factor V Leiden mutation and prolonged immobility, and the need for individualized multidisciplinary management.