A 70-year-old right-handed woman comes to the emergency department with left-sided visual loss that she noticed on awakening in the morning. She has no headache, slurred speech, difficulty swallowing, weakness, or difficulty walking. Her other medical problems include hypertension, atrial fibrillation, and hyperlipidemia. Blood pressure is 170/102 mm Hg and pulse is 90/min and irregular. On neurologic examination, she is alert and oriented to person, place, and time. Her speech is fluent, and she follows complex commands. Examination of her visual fields shows left homonymous hemianopia with macular sparing. There is decreased sensation over the left side of her body. The remainder of the neurologic examination is within normal limits. Non-contrast head CT demonstrates an area of focal parenchymal hypoattenuation, as shown in the image below.