CPT code 35508 represents an open surgical carotid-to-vertebral artery bypass graft used to restore vertebrobasilar perfusion by bypassing an occluded vessel. This complex vascular procedure is important nationally because it addresses high-risk cerebrovascular insufficiency where endovascular options may be limited or have failed. The code captures a resource-intensive operative service with implications for hospital utilization, surgical specialty billing, and payer medical necessity review. Key payers covered in the national analysis include Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare. Readers will learn the clinical context for use of 35508, typical sites of service, and payer coverage patterns. The publication also summarizes common modifiers and documentation elements used in billing, discusses expected surgical service lines and specialties involved, and highlights benchmarking considerations and policy factors that affect prior authorization and reimbursement. Data not available in the input is indicated where applicable.