Quiz case: a clinical reasoning challenge in the emergency stroke setting.

A right-handed woman in her 80s was admitted to the emergency department 1 h after sudden-onset global aphasia and right-sided hemiparesis. Medical history included arterial hypertension, dyslipidemia, hyperuricemia, aortic stenosis, osteoporosis, and recent pulmonary embolism. Medication consisted of apixaban, bisoprolol, hydrochlorothiazide, allopurinol, fenofibrate, and vitamin D. Vital parameters (blood pressure, heart rate, body temperature, oxygen saturation) and glycemia were all within normal range. Electrocardiogram showed a first-degree atrioventricular block. The patient was promptly transported to the emergency computed tomography (CT) scanner. Non-contrast brain CT revealed a unilateral hyperdensity in the left caudate and lentiform nuclei. No other intracranial lesion was visualized. Laboratory studies were not yet available at the time of imaging. What is your diagnosis?