Clinical Reasoning: A 76-year-old man with acute-onset left-sided weakness and numbness

A 76-year-old right-handed man with no known medical problems presented 2 hours after falling at work due to the acute onset of left-sided weakness and numbness. He had experienced left knee pain the previous day, but denied vertigo, headache, neck pain, chest pain, abdominal pain, or back pain. On examination, his blood pressure was 230/118 mm Hg; pulse and respiratory rate were normal. He was anxious with normal mentation, no carotid bruits, normal cardiac rate and rhythm, clear lung fields, normal cranial nerves including facial strength, weakness in his left leg (2/5 power) and arm (4/5 power), sensory loss to painful stimuli in his left face, arm, and leg, and normal deep tendon reflexes with plantar responses bilaterally.