Bihemisphere Ischemia Due to a Unilateral Lesion: A Case Report.

Bihemispheric ischemic strokes secondary to unilateral vessel disease are uncommon. We present the case of a 70-year-old man with multiple acute/subacute bilateral infarcts. The patient was found to have stenosis of the left internal carotid artery secondary to herpes zoster ophthalmicus vasculopathy, with involvement of the left proximal middle and anterior cerebral arteries. Angiographic studies also revealed A1 segment aplasia of the right anterior cerebral artery (ACA), thus indicating dependence on the left-sided circulation for perfusion of the bilateral ACA vascular territory. This case illustrates how A1 segment aplasia, an anatomic variant of the circle of Willis detected by angiographic studies, can contribute to bilateral infarction in the ACA vascular territory.