Left vertebral artery arising from the external carotid artery: an uncommon anatomical variant.

Purpose: To report an uncommon origin of the vertebral artery with embryological and clinical emphasis.

Methods: A 55-year-old male with sepsis presented with altered level of consciousness. Head computed tomography (CT), and CT angiography of head and neck vessels (CTA) were performed in the stroke code setting. An analysis of his vertebral artery system on CTA with 3D modeling was performed to assess the embryology of a vertebral artery arising from the external carotid artery, RESULTS: CTA revealed a dominant left vertebral arising from the left external carotid artery, the artery enters the transverse foramen at C2 and curves back behind the lateral mass of C1 entering the skull through the foramen magnum. The right vertebral artery was hypoplastic.

Conclusion: Anatomical variants of the vertebral artery origin are asymptomatic, and they are the result of the persistence of anomalous anastomosis during early fetal life. Vertebral artery origin from the external carotid artery as seen in our case is explained by the persistence of the second cervical intersegmental artery. Awareness of this anatomical variant is essential to avoid misdiagnosis, and for surgical and endovascular treatment planning.