A 56yo pt w/DM and HTN who smokes complains of the acute onset of vertigo, nausea, vomiting and unsteady gait. Examination shows decreased sensation to pinprick in the left side of the face, ataxia of the left upper and lower extremities, nystagmus and hoarseness. As the patient walks, they veer to the left. The most likely diagnosis is:
Select one of the following: