We described an 88-year-old woman presented with large aneurysm on the carotid siphon of the right internal carotid artery (ICA). Digital subtraction angiography showed extravasation from the distal cervical segment of the right ICA due to positioning a guiding catheter for intra-aneurysmal coil embolization. Transoral carotid ultrasonography (TOCU) showed arrested bleeding and a pseudolumen in the distal cervical segment of the right ICA. We originally described that TOCU was useful for evaluating iatrogenic extravasation and extracranial ICA dissection during neurointervention.