Q. A 55-year-old woman is brought to the emergency department because of a sudden onset of hemiparesis and blurred vision. On examination, she has left-sided facial palsy, horizontal left gaze palsy, and right-sided hemiparesis with increased deep tendon reflexes on the same side. She has a history of hypertension, type 2 diabetes mellitus, and asthma. She has smoked two packs of cigarettes daily for the past 20 years. What is the most likely cause of these symptoms?