A clinicopathological study of dissecting aneurysms of the intracranial vertebral artery.

Five autopsied cases of dissecting aneurysms of the intracranial vertebral artery are reported and the literature is reviewed to clarify the clinicopathological correlations. In an autopsy series of 110 patients with subarachnoid hemorrhage (SAH), the incidence of this entity was 4.5%, with all five cases progressing rapidly to death from massive SAH. Cases of intracranial vertebral dissection can be divided clearly into two groups based on the clinical and pathological features. In the first group, the dissection is confined to the vertebral artery and a massive SAH develops caused by the rupture of the arterial wall. The plane of dissection is mainly subadventitial. In the second group, brain-stem infarction develops resulting from luminal occlusion by intramural hematoma. The plane of dissection is mainly subintimal, with the dissection extending to the basilar artery. The condition in the second group affects patients at a younger age. If the lesion is localized within the vertebral artery and does not extend to the basilar artery, the disease seems not to be fatal. The clinical features of the vertebral dissection are largely determined by the plane and extension of dissection. Vertebral artery dissection is due to many causative factors including hypertension, congenital or degenerative changes in the arterial wall, and anatomical and pathological characteristics of the vertebral artery.