Background: Spontaneous occlusion of a giant aneurysm with its parent artery is relatively rare. Complete occlusion of a giant aneurysm at the basilar bifurcation and a basilar artery due to the dissection of the basilar artery has never been reported.
Case description: This 62-year-old man presented with left hemiparesis and right oculomotor palsy. Radiographic study showed a giant aneurysm at the basilar artery bifurcation with hemorrhage in its wall and an ischemic area in the right midbrain. Subsequent study revealed that thrombosis of the aneurysm rapidly progressed and that the parent basilar artery caused the dissection. Finally the giant aneurysm and the basilar artery were completely thrombosed.
Conclusion: The dissection was considered to occur in the aneurysm wall first by the hemorrhage in it and progress proximally along the basilar artery. Intramural hemorrhage in the wall of a giant aneurysm can be a cause of dissection of its parent artery. This seems to be one of the mechanisms by which a giant aneurysm and its parent artery are spontaneously thrombosed.