Unusual course of the vagus nerve passing anterior to the internal carotid artery during carotid endarterectomy

BACKGROUND: Carotid endarterectomy (CEA) is a conventional surgical technique to prevent ischemic stroke and the effectiveness for advanced lesions is established in many large studies. The vagus nerve is one of the cranial nerves that we usually encounter during CEA manipulation, which is identified as located posterior to the vessels in a position posterolateral to the carotid artery and posteromedial to the internal jugular vein. CASE DESCRIPTION: We experienced an extremely rare case of the vagus nerve passing anterior to the internal carotid artery during CEA. CONCLUSION: We should be careful not to accidentally cut off because the variation of the vagus nerve can be mistaken for an ansa cervicalis. A delicate and complete dissection to understand the variation of the vagus nerve is crucial to minimize the risk of cranial nerve injury during CEA.