Clinico-radiological study of collateral circulation after internal carotid and middle cerebral occlusion.

The intracranial collateral channels apart from the circle of Willis have been studied angiographically in 34 patients with internal carotid artery occlusion and 19 with occlusion of the middle cerebral artery. These collaterals are present in a high percentage of cases within a week of the ictus and are more common when the stroke has developed slowly. Their presence in occlusion of the middle cerebral artery seems to offer some protection against infarction but in internal carotid artery occlusion they are less important than the circle of Willis and when present suggest inadequacy of this structure.