An 84-year-old man with a lengthy history of smoking survived a small myocardial infarction 2 years ago. He now reports chest and leg pain during exercise. On physical examination, his vital signs are temperature, 37.1deg C; pulse, 81/min; respirations, 15/min; and blood pressure, 165/100 mm Hg. Peripheral pulses are poor in the lower extremities. There is a 7-cm pulsating mass in the midline of the lower abdomen. Laboratory studies include two fasting serum glucose measurements of 170 mg/dL and 200 mg/dL. Which of the following vascular lesions is most likely to be present in this patient?