Fig. 1. A : Computed tomography at admission showed a large subarachnoid hemorrhage and an intraventricular hemorrhage. B : Vertebral angiography revealed proximal narrowing with aneurysm dilatation ("string and pearl" sign) (arrow), suggesting a dissecting aneurysm at the lateral medullary segment of the left posterior inferior cerebellar artery. The artery ran in an unusual pattern, forming dual loops at the lateral medullary segment. C : Dissecting aneurysm and its parent arteries were illustrated by the senior surgeon (blinded for review). D : Occipital artery (arrowheads) is shown via common carotid artery angiography because selection of the external carotid artery failed due to its extreme tortuosity. Its distal segments, candidates for bypass graft, become abruptly narrow.