A ruptured dissecting aneurysm of the vertebral artery: comparison of angiographic and histological findings.

We present autopsy findings in a patient with a dissecting aneurysm of the vertebral artery causing subarachnoid haemorrhage. We sectioned the artery longitudinally and compared it with the angiogram, which showed the "pearl-and-string". Histological examination showed a pseudoaneurysm covered by adventitia alone, forming the "pearl". Internal elastic lamina and media were destroyed, and haematoma extended in the subadventitial space of the wall of the pseudoaneurysm. Media thickened by haematoma caused the "string", narrowing the parent artery. Alcian blue staining showed that stratified internal elastic lamina in the aneurysm and the parent artery, had undergone marked mucoid degeneration, which may have been responsible for the dissection.