A 24-year-old male, previously healthy, woke up with retroauricular pain. After 1 day, he developed left-sided facial droop and decreased taste sensation on the right side of the tongue. He experienced hyperacusis and right eye discomfort. No diplopia, tinnitus, hearing loss, or limb weakness were noted. Examination: inability to frown, raise eyebrows, or close the right eye; left-sided facial droop on grinning; decreased taste sensation on the anterior right tongue. All of the following should be considered for differential diagnosis EXCEPT: