Intracranial arteriovenous malformations: histopathological features

Arteriovenous malformations (AVM) are congenital abnormalities that consist of tangled masses of tortuous arteries, veins and abnormal connecting channels, that apparently result from the lack of development of the local capillary bed. Because of their propensity to bleed, arteriovenous malformations clinically constitute the most significant group of vascular malformations and the most frequent type in surgical specimens. On histologic study, the lesion is composed of arteries with muscular and elastic laminae, veins dilated by the pressure to which they are exposed because of the shunting and ambiguous vessels with both arterial and venous characteristics called arterialized veins. The pathological blood vessels are separated by brain parenchyma that often shows gliosis and hemosiderin pigmentation. The histologic composition of AVM generally permits confident recognition. The pathogenesis of vascular malformations likely involves the abnormal assembly, differentiation of vascular smooth muscle cells in association with dysmorphic vessel wall. AVM exhibit distinct pattern of expression of molecular markers of differentiation and maturity of VSMC as well as vascular endothelial growth factors and their receptors.