A revised concept of the congenital nature of cerebral arteriovenous malformations.

SUMMARY: Cerebral arteriovenous lesions are in general considered to be congenital in nature despite the fact that there is no evidence that the AV shunts diagnosed in adults are present at birth in a similar format. Construction of a vascular structure is the result of complex biological influences starting in the embryo, and continuing in the foetus, the neonate and the young infant. This vascular tree has to be maintained, repaired and modified according to metabolic demands, requiring over time the renewal of the entire structure. This is also genetically programmed and controlled. Both construction and maintenance involve repetitive steps and feedback towards the vascular tree according to the demands. Alterations in the programme or in the cellular logistics to achieve it, will create a different construction of the blood vessel wall. Analysis of the origin of the cerebrofacial endothelial cell would suggest that, the earlier a causative event occurs the larger the area of impact, and the higher the chances of apparent multifocality will be. The later the trigger occurs the more focal the defect and the smaller the lesion. If so, growth of an AVM as such should not occur; large nidi will not result from the growth of smaller ones. The impact of Rendu-Osler-Weber (ROW) disease on the venous endothelial cells and the polymorphism observed in cerebral arteriovenous shunts in ROW patients may outline the role played by the veins as the primary target in the development of cerebral AVMs. The venous and arterial angiopathy related to chronic high flow (or flow changes beyond normal equilibrium) impact a normally reacting vasculature which has been "abnormally" triggered by an AVM. This intraluminal trigger represents a "stress trigger" which can be flow, pressure or "other" related factors. This interpretation identifies the so-called AVMs to be the expression of various diseases rather than the disease itself They are the result and negative impact of biological dysfunction of the remodelling process at the capillarovenous junction.