Abstract
PURPOSE: The vertebral artery (VA) typically enters the subarachnoid space at the atlanto-occipital region. However, segmental variations can occur, with the VA entering the spinal canal at atypical levels. While a C3 segmental VA has been reported, no prior studies describe a C5 segmental VA. This case represents the first documented occurrence of this anomaly. METHODS: An 8-year-old girl underwent brain magnetic resonance imaging for headache screening, which incidentally revealed an abnormal VA course. RESULTS: Imaging revealed the absence of the left VA at the proximal V2 segment. Instead, a radiculomedullary artery at C4/5 entered the spinal canal and contributed to the formation of the anterior spinal artery (ASA), which ascended along the spinal cord. The right VA appeared normal; however, a radiculomedullary artery at the C3/4 level was identified, joining the contralateral radiculomedullary artery at the C1 level to form the ASA. Additionally, bilateral accessory middle cerebral arteries were observed. No clear association was found between this anomaly and the patient's headache, and she remained under observation. CONCLUSION: This anomaly may result from persistence of the fifth intersegmental artery. The vascular course resembled collateral circulation observed in acquired VA occlusion. Given its proximity to the spinal cord, potential risks include ischemic complications and spinal cord compression. This case highlights the importance of accurate imaging and careful surgical planning. Further studies on these rare vascular anomalies will enhance our understanding of VA variations and their clinical significance.