Extensive Left Sided Venous Thrombi and Bilateral Pulmonary Emboli in the Context of May-Thurner Syndrome for a Patient Presenting with Acute Flank Pain: A Case Report

May-Thurner syndrome is an underappreciated differential in the context of deep venous thrombosis. It is a symptomatic congenital abnormality resulting from compression of the left common iliac vein, sometimes also referred to as iliac vein compression syndrome in the literature. This case reports the presentation of a female with acute flank pain to the emergency department following a recent laparotomy for a complicated tubo-ovarian abscess. She was subsequently diagnosed with a sub-acute thrombus extending from the left common femoral vein into the left inferior vena cava, as well as new bilateral pulmonary emboli. As the patient had relative contraindications to thrombolysis, a shared decision was made with the vascular team to opt for conservative management only. In this instance, this included long-term oral anticoagulant therapy and compression stockings. This case asserts that clinicians should maintain a high index of suspicion for May-Thurner syndrome in the context of extensive left-sided thrombus formation.