ASCENDING AORTIC DISSECTION CAUSING UNILATERAL ABSENCE OF PERFUSION ON LUNG-SCANNING

A case of an ascending aortic dissection occurring in a patient 8 year s after an aortic valve replacement is presented. The patient's initia l clinical presentation was thought to be due to pulmonary embolism, a nd a ventilation-perfusion lung scan demonstrated mismatched absence o f perfusion to the entire right lung. Aortography and findings at surg ery demonstrated a type A dissection of the ascending aorta. The anato mic relationship of the aorta and pulmonary artery and their common tu nica adventitia make the right pulmonary artery susceptible to extrins ic compression after aortic dissection. Although uncommon, dissection of the ascending aorta needs to be considered in patients who have und ergone previous aortic valve surgery and demonstrate mismatched unilat eral absence of perfusion to the right lung. Because anticoagulation i s contraindicated in patients with acute aortic dissection, confirmati on of the diagnosis with angiography usually is required.