Crossing the Septum: May-Thurner Syndrome and Patent Foramen Ovale as a Dual Mechanism for Recurrent Ischemic Stroke

May-Thurner syndrome (MTS) is an anatomic venous compression disorder in which the left common iliac vein is compressed by the overlying right common iliac artery, predisposing patients to venous stasis and thrombosis. A patent foramen ovale (PFO) is a persistent interatrial communication that may permit paradoxical embolization when right-to-left shunting occurs. Although each condition is independently recognized, their coexistence as a potential mechanism for recurrent ischemic stroke is uncommon and may be overlooked when routine lower-extremity venous imaging is unrevealing. We present the case of a 70-year-old female with prior ischemic stroke, pulmonary embolism, and deep vein thrombosis (DVT) on chronic apixaban who presented with two days of isolated left upper extremity weakness. Brain magnetic resonance imaging (MRI) demonstrated an acute ischemic infarct in the right high frontal lobe involving the precentral gyrus. Bilateral lower-extremity venous duplex ultrasound was negative for acute DVT and did not demonstrate definite chronic post-thrombotic changes in the visualized femoropopliteal segments; however, this did not exclude proximal iliac venous pathology. Transesophageal echocardiography (TEE) demonstrated a PFO with right-to-left shunting. Pelvic magnetic resonance angiography demonstrated narrowing of the left common iliac vein from extrinsic arterial compression, consistent with MTS. The patient underwent balloon venoplasty of the left iliac vein and was referred for outpatient PFO closure evaluation. This case highlights the importance of expanded venous and cardiac evaluation in selected patients with recurrent or cryptogenic stroke and prior venous thromboembolism.