De novo vertebral artery dissecting aneurysm after contralateral vertebral artery occlusion--two case reports.

Two patients developed de novo vertebral artery dissecting aneurysm after contralateral vertebral artery occlusion. A 36-year-old man presented with brainstem ischemia and was treated non-surgically. Subsequent angiography showed spontaneous vertebral artery occlusion at the site of dissection. A 45-year-old man developed subarachnoid hemorrhage due to vertebral artery dissecting aneurysm. He underwent endovascular occlusion of the vertebral artery proximal to the dissecting aneurysm. These patients developed de novo dissecting aneurysm on the contralateral vertebral artery at 13 months and 11 days after unilateral vertebral artery occlusion, respectively. These cases strongly suggest that changes in hemodynamic stress due to unilateral vertebral artery occlusion are related to de novo dissecting aneurysm on the contralateral side. The risk of de novo dissecting aneurysm may be increased by proximal occlusion or trapping of dissecting aneurysm of the contralateral vertebral artery.