This procedure is done to block off or close blood vessels. This treatment can often significantly improve venous and arterivenous malformations , as well as other vascular malformation problems, such as Klippel Trenaunay or Kaposiform Hemangendothelioma . A catheter is inserted into the blood vessel and an angiogram is performed (see above.) A substance is then injected into the vessel to seal off blood flow. This substance can be tiny particles, a liquid, coils, or a gel. This procedure may also be done to minimize bleeding before surgery.