[A 74-year-old man who underwent carotid artery stenting with symptomatic right internal carotid artery stenosis with congenital agenesis of the left internal carotid artery].

A 74-year-old man visited our hospital with a 1-month history of awareness of wobbling while walking. Head MRI revealed fresh cerebral infarction in the territory of the right middle cerebral artery, and cervical carotid ultrasonography revealed severe stenosis at the origin of the right internal carotid artery. No left internal carotid artery could be confirmed, and no carotid canal was evident on CT of the head, suggesting congenital agenesis of the left internal carotid artery. Carotid artery stenting was performed for the stenosed right internal carotid artery that was refractory to medical treatment, obtaining a good outcome. Patients with congenital internal carotid artery agenesis show unique hemodynamics and anatomical features. Particularly in cases with cerebral infarction, an understanding of the etiology and complicated classification of disease types is needed, in addition to familiarity with comorbidities.