Aplasia of the left common carotid artery with internal and external carotid arteries lacking separate origins and concomitant carotid–anterior cerebral artery anastomosis: a rare case report and literature review

Aplasia of the common carotid artery (ACCA) is a rare vascular anomaly. Patients are typically asymptomatic unless accompanied by other vascular abnormalities. This condition is usually associated with independent origins of the internal and external carotid arteries, whereas cases without separate origins are particularly rare, with fewer than ten reported in the literature. Carotid–anterior cerebral artery (ACA) anastomosis is a rare embryological vascular variant characterized by an anomalous connection between the pre-ophthalmic segment of the internal carotid artery and the A1 segment of the ACA. To the best of our knowledge, no cases of concomitant ACCA and carotid–ACA anastomosis have been reported to date. A 24-year-old man was incidentally found to have aplasia of the left common carotid artery during imaging evaluation for scoliosis. The left internal carotid artery and external carotid artery lacked separate origins and instead arose a normal carotid bifurcation at the C4 vertebral level. In addition, the brachiocephalic artery was absent, with the aortic arch sequentially giving rise to the right common carotid artery, right subclavian artery, and left subclavian artery. Extensive collateral circulation among the left deep cervical artery, occipital artery, and ascending cervical artery was observed at the C2 vertebral level, accompanied by retrograde flow within the left external carotid artery and superior thyroid artery. Intracranial CTA further revealed multiple anatomical variations of the circle of Willis, including a trident-shaped anterior communicating artery, aplasia of the left posterior communicating artery, a right-sided partial fetal posterior cerebral artery, and a right-sided carotid–ACA anastomosis with ipsilateral ACA A1 segment hypoplasia. As the patient was asymptomatic, no vascular intervention was performed. Ultrasonography is the first-line diagnostic modality, while computed tomography angiography with three-dimensional reconstruction provides complementary and comprehensive anatomical assessment. Accurate recognition of such vascular anomalies is crucial, as it can reduce the risk of iatrogenic injury associated with atypical vascular pathways and facilitate evaluation of potential cerebrovascular complications. Not applicable.