Brainstem Stroke Presenting as Wake-Up Diplopia in a Patient With an Incomplete Circle of Willis

We present the case of a 65-year-old patient who suffered a wake-up brainstem stroke. The only symptom reported by the patient was double vision. Upon examination, she was found to have left internuclear ophthalmoplegia and ipsilateral downbeat nystagmus. Magnetic resonance angiography revealed a unilateral partial fetal posterior cerebral artery and unilateral posterior communicating artery hypoplasia. The patient was ineligible for intravenous thrombolysis: she evolved favorably with anti-platelet medication and was discharged after five days. We put forth a discussion on the clinical significance of these physical exams and magnetic resonance imaging findings.