The close connection between the intracranial vascular system and the blood supply of the splan- chnocranium makes in case of stenoses or obliterations the development of a collateral circulation from the area of the external carotid artery possible. The most frequent route of communication is the ophthalmic artery into the carotid artery and the occipital artery into the vertebrobasilar area. However meningeal arteries also play an important part in the development of collateral circulati- ons. By the same route, however in a reverse direction a collateral circulation develops from the area of the neurocranium to the area of the ACE. Causes include stenoses, occlusions and embolism of the ACE, haemorrhage, vascularized tumours and AVM. Usually the collateral circulation is not of such an extent to lead to ischaemic cerebral changes. Only in extensive AVM in the area of the splan- chnocranium permanent cerebral hypoxia develops. Focal changes are rare.

        Key words: head and neck - AVM - intracranial collateral circulation - cerebral ischaemia