A right eye amaurosis patient with congenital absence of the internal carotid artery

Rationale: Absence or hypoplasia of the internal carotid artery (ICA) are rare developmental anomalies. Usually, patients with ICA agenesis are asymptomatic due to collateral circulation, but they may present with seizures, headache, or transient ischemic attack. We report a patient with right ICA absence in whom “paroxysmal right eye amaurosis” was the main symptom. Patient concerns: A 76-year-old male patient suffered from “paroxysmal right eye amaurosis for 3 years”. Three years prior, the patient had suffered sudden one-minute right eye amaurosis without any obvious cause. The attack reoccurred 1–2 times/year until one week before admission when he experienced two sudden right eye amaurosis. Diagnosis: Congenital absence of the right ICA was diagnosed. In this patient with congenital absence of the right ICA, the ipsilateral anterior cerebral artery (ACA) was compensated by the anterior communicating artery (ACOM), and the ipsilateral middle cerebral artery (MCA) emerged from the carotid siphon of the contralateral ICA. Interventions: The patient was given antiplatelet treatment consisting of aspirin and atorvastatin after admission and instructed to maintain the treatment after discharge. Outcomes: No symptom onset was observed during follow-up. Lessons: Here, we report the patient's clinical manifestations and imaging findings and analyze the cause of the condition to provide a clinical reference for the study of congenital absence of the ICA.