A 62-year-old man with a history of hypertension is brought to the emergency room with severe left chest and back pain. His blood pressure is 80/50 mm Hg. Physical examination shows pallor, diaphoresis, and a murmur of aortic regurgitation. An ECG does not show myocardial infarction. An X-ray film of the chest reveals mediastinal widening. Which of the following is the most likely diagnosis?

Aortic dissection reflects hemorrhage between and along the laminar planes of the media, with the formation of a blood-filled channel within the aortic wall. If it begins in the ascending aorta, it may extend backward toward the aortic valve or distally to involve the thoracic and abdominal aorta. More than 90% of dissections occur in men between the ages of 40 and 60 with antecedent hypertension. The second major group of patients, usually younger, has a systemic or localized abnormality of connective tissue that affects the aorta (e.g., Marfan syndrome). Although bacterial endocarditis (choice A) can result in aortic regurgitation, it does not lead to acute chest pain. The other choices are not associated with aortic regurgitation.Diagnosis: Aortic dissection