Types of arteriovenous malformations

Schematic drawing of Yakes classification of AVMs.

Type I – Direct artery-to-vein connection (ie, arteriovenous fistula [AVF]), typified by pulmonary AVF and renal AVF, for example. This angioarchitecture type is not specifically described in the Houdart or Do classification systems.

Type II – AVM characterized usually by multiple inflow arteries into a "nidus" pattern with direct artery-arteriolar to vein-venular structures that may not (type IIa) or may be (type IIb) aneurysmal.

Type IIIa – AVM with multiple arteries-arterioles connecting microfistulae into the wall of an enlarged aneurysmal vein with an enlarged single outflow vein.

Type IIIb – AVM with multiple arteries-arterioles connecting microfistulae into the wall of an enlarged aneurysmal vein with multiple dilated outflow veins.

Type IV – AVMs are microfistulous innumerable arteriolar structures shunting into innumerable venular connections that diffusely infiltrate a tissue (typified by ear AVMs that infiltrate the entire cartilage structure of the pinna).