Accessory left vertebral artery with the inferior thyroid branch: A report of anatomical variant.

Background: Awareness of the anatomical variations of the vertebral arteries is critical in the diagnosis and management of the related neurovascular pathologies. This study describes a rare anatomical variant of an accessory left vertebral artery (ALVA).

Case description: An 88-year-old female with a chronic subdural hematoma was admitted to our hospital for embolization of the left middle meningeal artery. Pre-procedural imaging revealed an ALVA (medial branch) arising directly from the aortic arch between the origins of the left common carotid artery and the left subclavian artery. The ALVA runs directly from its origin toward the vertebral foramina and gives off the left inferior thyroid branch at the mid-point of its course, then unites with the left vertebral artery (LVA) (lateral branch) at C4 level and courses through the C6 foramina transversaria. The left thyrocervical trunk has no inferior thyroid branch. Digital subtraction angiography was obtained and confirmed the above-described findings. There was no evidence of stenosis or flow restriction at the anastomotic site between the ALVA and LVA. The patient has no symptoms related to the LVA anatomical variant. The right vertebral artery was larger than both LVAs. The ALVA was smaller in size as compared to the LVA.

Conclusion: This case highlights a rare anatomical variant involving an ALVA with an inferior thyroid branch. Awareness of such atypical vascular branching patterns may impact the safety and precision while treating-related neurovascular diseases of the head and neck.