Fenestration of the vertebrobasilar junction.

A fenestration of the vertebrobasilar junction was found in an 80-year-old man during autopsy. It was associated with thrombosis of the vertebral arteries which had caused a left Wallenberg syndrome. The left limb of the fenestration presenting the same transverse diameter as that of the remaining part of the basilar artery appeared to be its direct (true) origin. The right limb had a lesser transverse diameter and appeared to bridge the lateral surface of the rostral end of the right vertebral artery and the basilar trunk. According to the authors, this fenestration could have been caused by the persistence of the cranial part of a primitive lateral vertebrobasilar anastomosis, rather then by the usual incomplete fusion of the primitive paired basilar arteries.