[A characteristic magnetic resonance image of a dissecting aneurysm in the vertebrobasilar system].

Recently several reports of dissecting aneurysm in the vertebrobasilar system have been published. We report the effectiveness of MRI for the detection of a dissecting aneurysm in the vertebrobasilar distribution system. A 47 year-old male [correction of female] was admitted to our hospital due to right occipitalgia and the right Wallenberg's syndrome. Computed tomography disclosed no abnormalities. Cerebral angiogram showed the pearl and string sign of the right vertebral artery, which suggested a dissecting aneurysm. MRI exhibited the infarct area at the right dorsolateral part of the medulla oblongata, which corresponded to right Wallenberg's syndrome. It disclosed high intensity ring-like findings circumscribing a low intensity spot of the lumen of the right vertebral artery. This high intensity was thought to be the hematoma between the intima and the media at the subacute stage. Its high intensity corresponded to the site of the dissecting aneurysm and of Wallenberg's syndrome. These findings are thought to be useful in the diagnosis of a dissecting aneurysm of the vertebral artery.