Rare and combined vertebrobasilar dysplasias related to vascular maldevelopment at different embryonal stages.

Angiographically demonstrated combined and complex angiodysplasias of the vertebrobasilar system are rare. As in our case, they can be attributed to a vascular maldevelopment in several consecutive embryonal stages: the angioma-like arterial network of the left posterior cerebral artery and the non-union and overcrossing of the vertebral arteries in the region of the prepontine cistern represent an early defect (up to 15 mm stage); the aneurysmatic ectasia of the right vertebral artery with a second pedunculated aneurysm at its uppermost part may be due to a later defect (up to 40 mm stage) of the cerebral vascular development.