A type II proatlantal artery arising from the external carotid artery: A review of neurovascular anatomy.

Background: A type II proatlantal artery is a rare congenital vascular anomaly comprised of a persistent embryologic connection between the carotid and vertebrobasilar circulations. Although generally asymptomatic and detected incidentally, its identification is of clinical importance in neurovascular assessments and interventions. Case Description: A 70-year-old male presented with acute-onset left lower extremity weakness and numbness, out of the window for thrombolytics; computed tomography angiography of the head and neck incidentally identifying a persistent left type II proatlantal artery originating from the external carotid artery and supplying the vertebrobasilar circulation. Magnetic resonance imaging of the brain the following day was unremarkable for acute infarction or other cerebrovascular pathology. Conclusion: This case underscores the significance of recognizing congenital vascular anomalies such as the type II proatlantal artery, particularly in the context of cerebrovascular assessment. Although these variants are often incidental and not associated with increased stroke risk, their presence has implications for neuroendovascular procedures and stroke evaluations. Understanding the anatomic and embryologic origins of these vascular anomalies facilitates accurate interpretation of cerebrovascular imaging and enhances clinical decision-making in patients with these anomalies.