A 70 year-old semiretired janitor with a history of hypertension, went to work one morning and at 7:00 am he had sudden onset of nausea, vomiting, and unsteadiness. He was taken to the emergency room, where his exam was notable for slurred speech with slowed tongue movements, dysmetria on finger nose testing on the left, dysmetria on heel shin testing on the left, and left dysdiadochokinesia. Upon attempting to stand, he fell to the left, even when he kept his eyes open. The remainder of the exam was unremarkable.
Localization and differential diagnosis
1. On the basis of the signs and symptoms shown in bold above, where is the lesion?
2. What is the most likely cause?