Complex Vertebral Artery Variation at the Craniovertebral Junction With V3 Segment Fenestration and External Carotid Artery-Derived Collateral Reconstruction

Background: The vertebral artery (VA) develops through a complex embryological process, and various anatomic variations may be encountered in adults. Vertebral artery fenestration (VAF) is a rare congenital vascular anomaly that may mimic vertebral artery dissection on imaging and requires careful differentiation based on vascular morphology and imaging findings. The coexistence of vertebral artery origin nonopacification, fenestration, and external carotid artery-derived collateral circulation is uncommon. Case Presentation: A 45-year-old man with no history of cerebrovascular disease or conventional vascular risk factors underwent magnetic resonance angiography (MRA) during a routine health examination. MRA revealed multiple cerebrovascular abnormalities, including bilateral vertebral artery stenosis, terminal basilar artery fenestration, persistent fetal-type right posterior cerebral artery, distal stenosis of the bilateral posterior cerebral arteries, stenosis at the bilateral anterior cerebral artery A1/A2 junctions, and cerebral atherosclerotic changes. The patient was asymptomatic, without neurological manifestations such as headache, dizziness, nausea, vomiting, diplopia, rotational vertigo, choking during drinking, dysphagia, or bowel and bladder dysfunction. Whole-brain digital subtraction angiography (DSA) was subsequently performed to further characterize the vascular anatomy. Digital subtraction angiography demonstrated nonopacification of the origin of the right vertebral artery, suggesting proximal occlusion. Selective right external carotid artery angiography revealed collateral vessels originating from branches of the deep cervical artery, costocervical trunk, and occipital artery. These vessels provided collateral supply to the V3 segment of the right vertebral artery through muscular anastomoses, resulting in reconstitution of the distal vertebral artery and visualization of the posterior circulation. Conclusion: This case demonstrates a rare pattern of complex vertebral artery anatomic variation. DSA not only identified the location of vertebral artery occlusion but also demonstrated the origin of abnormal collateral circulation and the pattern of vascular reconstruction, providing important diagnostic information for complex vertebral artery variations.