Case History: Case K

A 68-year-old man had a 10-year history of poorly controlled hypertension. He awoke one morning with right-sided weakness, especially involving his right hand. His condition progressed over the next few hours, and in the emergency department he had dense paralysis of the right upper extremity, weakness of the right lower extremity, and difficulty speaking (he could utter "yes," "no," and a few other words, and could understand spoken language). CT scan was unremarkable (see image). Based on the history, what is the most likely diagnosis?