Cerebral arterio-venous malformations

A cerebral arterio-venous malformation (AVM) usually consists of a group of abnormal vessels (the " nidus ") formed around one or more direct connections (shunts) between the arteries and veins in the brain. The absence of capillaries at the interface between the shunts decreases vascular resistance and leads to haemodynamic perturbations at various levels : acceleration of the arterial blood flow and increase in blood flow rate,  drop in pressure in the small cerebral arteries and increased venous pressure downstream from the malformation.

An AVM can cause intracerebral bleeding.