Special types — Arteriovenous malformation

An arteriovenous fistula (AVF) is an abnormal, direct and simple connection between an artery and a vein as opposed to a typical AVM where the connections are multiple complex, net-like structures. In this condition, the capillary bed that normally connects arteries and veins is bypassed, creating a short-circuit connection (shunt). An arteriovenous fistula can be congenital or acquired, e.g., through trauma.

A congenital arteriovenous fistula is the simplest form of arteriovenous malformation (AVM) with a direct connection. Like all vascular malformations, congenital AVFs are not acquired. The vessels that form the short-circuit connections between the arterial and venous systems in an arteriovenous malformation can vary in number, diameter, length and configuration, and are collectively referred to as the nidus.

On account of the rapid flow of blood within an arteriovenous fistula and an arteriovenous malformation, these are classified as fast-flow lesions. Peripheral arteriovenous malformations that are not located in the central nervous system may occur in any organ system and may have superficial, deep or combined forms of extension. This variability is also reflected in the broad range of clinical appearances of arteriovenous malformations. The most common anatomical locations of an arteriovenous malformation are the neck/head area (47.4%) and the extremities (28.5%).

This is a rare, often autosomal dominant disease which, in contrast to the more widespread spontaneously occurring arteriovenous malformation, is characterized by a mutation in the RASA-1 gene. Multiple, rather small capillary malformations of the skin usually occur in several family members with the simultaneous presence of one or more arteriovenous malformations in different locations. The spectrum ranges from uncomplicated capillary changes to the skin to the simultaneous presence of large, multiple arteriovenous malformations.