Lesson of the month 2: A rare presentation of stroke: diagnosis made on magnetic resonance imaging.

Bilateral thalamic infarcts are uncommon posterior circulation strokes. The artery of Percheron (AOP) is a rare anatomical variant involving a singular arterial supply to both thalami and occlusion leads to bilateral thalamic infarction.We report the case of a 71-year-old man who presented with decreased consciousness (fluctuating Glasgow Coma Scale score of 5-7). He had a background of atrial fibrillation and was anticoagulated with dabigatran, a novel oral anticoagulant. Computed tomography (CT) scan showed a mildly reduced attenuation in the region of the left thamalus.Subsequent diffusion-weighted magnetic resonance imaging (MRI) showed acute brainstem infarction, extending into the thalamus bilaterally, likely due to AOP occlusion. Bilateral thalamic infarcts due to AOP occlusion may not be recognised on initial CT scan and are more readily seen using diffusion-weighted MRI, which is the most beneficial imaging modality to aid in early diagnosis and treatment. © Royal College of Physicians 2018. All rights reserved.