Embolization is useful in a broad spectrum of clinical situations. Embolization can be particularly effective in hemorrhage, regardless of whether the etiology is trauma, tumor, epistaxis, postoperative hemorrhage, or GI hemorrhage (see the images below). It can be performed anywhere in the body that a catheter can be placed, including the intracranial vasculature, head and neck, thorax, abdomen, pelvis, and extremities. With the availability of coaxial microcatheters, superselective embolizations can be performed. In most patients, embolization for hemorrhage is preferable to surgical alternatives.
Technique and Equipment
Embolization procedures begin with diagnostic angiography to identify the source of bleeding. For example, in epistaxis, angiography of the external carotid artery with attention to the internal maxillary artery can be helpful (see the images below). [1, 2, 3, 4] In pelvic fractures, the internal iliac arteries are examined angiographically. [5, 6]
Selective and superselective angiography is more sensitive in finding the source of bleeding than are nonselective studies. [2, 7, 8, 9, 10, 11] Consequently, clinical suspicion and the results of other imaging studies such as contrast-enhanced computed tomography (CT) scanning and radionuclide scans with technetium-99m (99mTc)–labeled red blood cells (RBCs) are important in guiding angiographic examination.
In intra-abdominal bleeding, such as after complex trauma, CT scanning may identify the site of acute bleeding, because acute bleeding often demonstrates higher density (Hounsfield units [HU]) than older blood; this is termed the "sentinel clot sign."  For angiograms of abdominal wounds, see the images below.
Hemorrhage is identified by active extravasation of contrast medium outside of the confines of the vessel lumen. The angiographic appearance depends on the rate and location of bleeding. The extravasating contrast medium may flow toward the dependent part of the viscus; in the bowel, the extravasated contrast may outline the mucosa. When the bleeding site and artery have been identified on the initial angiogram, a catheter, often a 3-French (3F) microcatheter, is placed as selectively as possible into the bleeding artery to confirm the bleeding and to stop it with embolization.
Angiography in the setting of lower gastrointestinal (GI) hemorrhage generally does not demonstrate unique diagnostic findings that explain the cause of bleeding, only the site of active bleeding. Thus, angiographic examinations during the episode of acute, brisk bleeding are required. In cases of recurrent occult GI bleeding, angiography can be performed electively in hopes of identifying a distinct finding such as angiodysplasia, arteriovenous malformations (AVMs), or intestinal varices. [12, 13]
Occasionally, provocative protocols that use angiography and infusions of lytic agents or heparin have been administered, although these techniques have provided mixed results. Carbon dioxide angiography may increase the yield of angiography in the acute GI bleeding scenario.
Pulmonary arteriovenous malformations (AVMs) usually are congenital lesions, although they may occur after surgery or trauma. The congenital form is highly associated with hereditary hemorrhagic telangiectasia, also termed Osler-Weber-Rendu Syndrome. There is a genetic predisposition to this condition. It is also associated with liver AVMs; however, preemptive treatment of the latter is presently unwarranted. Screening head CT scans or magnetic resonance images (MRIs) are important to exclude intracranial AVMs.