Paradoxical embolization in patients with cryptogenic stroke
BACKGROUND: The increased prevalence of patent foramen ovale (PFO) in patients with cryptogenic stroke suggests the occurrence of paradoxical embolism. Previous studies have found paradoxical embolism to be uncommon in stroke, but few have focussed on patients with cryptogenic stroke. We therefore evaluated pelvic veins and leg veins in this population. METHODS: Eighteen patients (median age 45 years) with a cryptogenic brain ischemic event (stroke 16, TIA 2) underwent magnetic resonance venography (MRV). Evaluation consisted of time-of-flight (TOF) and phase contrast images through the pelvis. A positive MRV was defined as an intravascular decrease in signal intensity at least 15 millimeters (mm) in length contacting the wall of a vein and showing matching abnormalities on both pulse sequences. Lower extremity venous duplex examination was also performed in 17/18. RESULTS: All patients had normal cranial arteries, apart from the artery referable to the index stroke. A right-to-left intracardiac shunt was identified in 16/18. MRV was performed a median of 22 days (range, 2–416) post-event. In three patients, only the TOF was performed (all negative studies). There were three patients who had evidence for paradoxical embolism. Patient 1 had sickle cell disease and two small cortical emboli, a PFO, a 30 mm left external iliac vein clot three days post-stroke, and a right calf vein clot diagnosed 23 days post-stroke. Patient 2 had a history of right knee injury and surgery, top of the basilar embolus, a PFO, and a chronic clot in the distal right popliteal vein. Patient 3 had several hours of sudden dysarthria and confusion after pelvic surgery, a PFO, and a right calf vein clot two days post-TIA. One patient had a basilar artery embolus and a 20 mm right external iliac vein clot, but no PFO. Another patient had no DVT day 2 post-stroke, but bilateral calf vein DVT on day 10. CONCLUSIONS: Pelvic MRV has diagnostic utility in the evaluation of patients with cryptogenic stroke. Pelvic vein and calf vein thrombosis are a source of paradoxical embolism in some patients with cryptogenic stroke. The incidence of thrombus in these two sites requires further evaluation in this population.