Arteriovenous malformations

An arteriovenous malformation (AVM) is a congenital malformation of the blood vessels in which arteries are directly connected to veins without any capillaries in between.

The vascular malformation consists of a network of direct connections between the arteries supplying blood and the veins carrying blood away, whereby it is often no longer possible to precisely delineate the AVM. Due to the increased blood flow within the AVM, the blood vessels are dilated and aneurysms may form. Due to the visual structure of the malformation, an AVM is also described as a vascular tangle. The center of the seemingly knotted blood vessels is called the nidus (Latin for “nest”).

Histologically, the structure of the blood vessels in the AVM area differs from that of “healthy” blood vessels; within the AVM, some wall layers of the arteries/veins are extremely thin or missing altogether. The blood vessels of the AVM are therefore more susceptible to rupture, which can lead to (internal) bleeding.

The size of an AVM is variable; the extent of the AVM can increase or decrease over time.

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