Q. A 78-year-old male was admitted two days ago following a ST-segment elevated myocardial infarction for which he underwent cardiac catheterization. The patient has a past medical history of hypertension, hyperlipidemia, and a previous myocardial infarction 5 years ago. His left coronary artery was found to have a significant stenosis in the proximal portion. Angioplasty and stenting was performed with good results. Left ventricular ejection fraction was measured at 40 percent. His right coronary artery was found to have moderate stenosis in the mid portion. The aorta and both iliac arteries showed severe atherosclerosis. There was no significant left to right shunting or evidence of right heart failure. The patient remains in the cardiac care unit, and staff report no hemodynamic issues overnight. While examining the patient this morning you note the patient has developed moderate weakness of his left upper extremity, left facial paralysis, and left homonymous visual loss. You order a contrast CT of the patient’s head and neck (see image). Based on the information you have at this point in time, what is the most likely underlying etiology of this patient’s new symptoms?