Ectasia of arteries beyond the circle of Willis.

Isolated fusiform ectasia involving branches of the carotid and vertebral arteries is very rare, only two cases have been recorded. Recently we have encountered two cases affecting the right posterior and left middle cerebral arteries. Both patients were young and there was no evidence of acquired arterial pathology. It is considered likely that the condition is a local congenital abnormality which may be related to an abnormality of the elastic substance in the arterial wall. In the first case, a selective injection of the right posterior cerebral artery clarified the nature of the lesion and provided an example of the value of the relatively new superselective technique.