(597) The Artery of Percheron: A Rare Anatomical Variant of Thalamic Infarcts

Introduction: The artery of Percheron (AOP) is an uncommon posterior cerebral branch, that is present in approximately 4%-12% of the population. We present a case of an elderly male with acute encephalopathy from bilateral thalamic infarcts of the artery of Percheron.

Description: An elderly male presented with acute encephalopathy. Physical examination was significant for bilateral pinpoint pupils, Glasgow Coma Scale score of eight and was therefore intubated for airway protection. Initial CT of the brain was concerning for a small acute infarct in the left thalamus. The patient was admitted to the intensive care unit for the management of an acute ischemic thalamic infarct. MRI without contrast was significant for bilateral thalamic infarcts associated with a left thalamic hemorrhage, with additional CT angiogram confirming ischemic changes in the AOP. After extubation, the patient was persistently noted to have bilateral vertebral gaze palsy, consistent with the bilateral thalamic infarcts.

Discussion: The AOP is a rare anatomical variant, from the P1 branch of the posterior cerebral artery, with an overall low incidence rate of all ischemic strokes. This artery supplies the bilateral thalamus and midbrain, which are highly sensitive to ischemic changes. Described in literature, are four subtypes of blood supply to the thalamus and midbrain. Type IIb contains the AOP and occurs in 25% of the general population, therefore making it the only identifiable source to cause bilateral thalamic infarcts in our patient. Due to the varying presence, diagnosis of an AOP infarct remains challenging, rendering it an imaging diagnosis. Up to 67% of patients with AOP infarction may demonstrate T2 FLAIR and DWI signal hyperintensity along the surface anterior medial midbrain, coined the “V sign”, however not demonstrated in this case. Differential for bilateral thalamic and basal ganglia restricted diffusion includes multiple etiologies including vaso-occlusive disorders (e.g., top of the basilar syndrome), infectious and toxic-metabolic pathologies. AOP infarction should be kept high in the differential, especially for cases in which other etiologies do not fit the clinical picture. In this case, clinical history and visualization of the rare artery on CT angiography cinches the diagnosis.