Arteriovenous malformations belong to a large group of cerebrovascular malformations and are composed of a blood supply artery, a draining vein, and an intermediate arterialized vein-like vessel (arteriovenous fistula). The normal vascular transition is from the arteries to the capillaries and then to the venous system, but in patients with arteriovenous malformations, the arteries drain directly into the venous system, and the lack of a capillary layer leads to direct arterial blood drainage into the venous system. Arterial blood is very rich in oxygen and usually appears as red or bright red. Venous blood is significantly less oxygenated due to the exchange of carbon dioxide or metabolic products by the tissues and appears dark red or dark brown, with a pale blue or blue-like pattern on the venous vessels. However, in patients with arteriovenous malformations, the arterial blood, which is rich in oxygen, rushes directly into the venous system without passing through the capillary transition, causing the walls of the veins, which should appear blue, to appear red, so that the arteries and veins cannot be distinguished well during surgery. If the arteries are not treated after the draining veins are treated first, the arteriovenous malformation cluster may rupture and bleed, making the operation difficult.