EMBOLIZATION TECHNIQUES AND
APPLICATIONS
33
Sara Chen Gavenonis, MD, and
S. William Stavropoulos, MD
1. Describe embolotherapy and some of its indications.
Embolotherapy is temporary or permanent vascular occlusion induced by the intravascular administration of materials
via a percutaneous route. Embolization has various clinical applications, including control of bleeding; treatment of
vascular malformations; and tumor or organ ablation for curative, palliative, or preoperative purposes.
2. What materials are most commonly used for embolization?
Various embolic materials are commercially available. The most widely used embolic materials are absorbable gelatin
sponge (Gelfoam), a temporary agent; metallic coils; and polyvinyl alcohol (PVA) particles. Specific clinical situations may
warrant the use of other agents, such as absolute ethanol, synthetic microspheres, or liquid  glues.
3. What is Gelfoam, and how is it used?
Gelfoam is a reabsorbable gelatin that is most widely used in its sheet form. Wedges (1 to 2 mm) of Gelfoam are divided
from the larger sheets. The Gelfoam can be injected as  torpedoes through a catheter placed in a blood vessel, or the
Gelfoam can be suspended in a contrast/saline slurry, which can be injected.
4. How does Gelfoam work? When is it used?
Gelfoam causes vascular occlusion by mechanically obstructing vessels, serving as a matrix for thrombus formation,
and by causing endothelial inflammation that incites further thrombus formation. Gelfoam is reabsorbed in 5 to 6 weeks,
during which time vessel recanalization is anticipated. Clinical situations in which temporary vascular occlusion is
preferred include pelvic arterial hemorrhage after trauma, priapism, peripartum hemorrhage, and some cases of upper
gastrointestinal (GI) bleeding. The rationale for using Gelfoam in these situations is based on the belief that the use of
a temporary agent would minimize the long-term ischemic effect on the end organ.
5. What are metallic coils?
Metallic coils are made of either stainless steel or platinum. Dacron fibers are woven into some coils to promote
thrombosis. Coils are available in a wide variety of shapes, sizes, and configurations. Special wires are used to push
the coils through catheters that have been placed into the vessel intended to be embolized. Coils occlude vessels by
causing mechanical obstruction, inducing clot formation, and provoking an inflammatory reaction.
6. When are coils preferred?
One way to classify embolic materials is based on whether they cause permanent or temporary occlusion. Another
way is based on the size (diameter) of the vessel where the occlusion occurs. Coils cause vascular occlusion in vessels
that are 1 to 2 mm in diameter and larger. Coils are preferred in clinical situations in which permanent occlusion is
intended in vessels of this size. This includes the treatment of arteriovenous fistulas, GI bleeding, aneurysms, endoleaks
after endovascular repair of abdominal aortic aneurysms, and traumatic vascular injuries in the proper clinical settings.
Coils should not be used if occlusion is desired in vessels smaller than 1 mm, including situations in which the target of
the embolization is an organ. When embolizing the uterus or performing chemoembolization of the liver, coils are not used.
PVA particles or ethanol can be used to cause microvascular thrombosis, depending on the specific clinical situation.
7. What happens when coils are the wrong size?
Although there is no TV show called  When Coil Embolization Goes Bad, any experienced interventional radiologist
can tell a good tale about inappropriately sized coils. When coils are undersized, they can remain mobile after they are
pushed out of the catheter and continue to travel with the flow of blood until they embolize to a vessel that is smaller
than the diameter of the coil. If this happens while a venous embolization is being performed, the coils travel back
toward the right heart and often out the pulmonary artery before lodging in a small vessel. The lungs are also a likely
final destination for coils that inadvertently pass through an arteriovenous fistula. When deployed in an artery, coils
that are too small can migrate into distal branches or into another vascular distribution. This migration may result in
241
C
H A P T E R
242 EMBOLIZATION TECHNIQUES AND APPLICATIONS
nontarget embolization and decreased efficacy of the intended embolization. Coils that are too large can partially recoil
into the parent vessel or cause the catheter to back out of the proper vessel. Retrievable coils are now available and
allow optimization of positioning, configuration, and sizing before full deployment.
8. When are PVA particles used?
PVA particles range in size from 50 to 2000 źm. Their mechanism of action is to obstruct vessels physically and incite
extensive granulation tissue formation. PVA particles result in permanent occlusion. The size of the particle used is
based on the location of desired thrombosis. The smaller the particles are, the more distal the embolization. Particle
selection is often based on the experience of the operator. If the particles selected are too small, end-organ ischemia
and necrosis may occur. If the particles are too large, collateral vessels may quickly reconstitute blood flow to the target
organ, significantly decreasing the efficacy of the procedure. The smallest particles are reserved for tumor embolization
or preoperative devascularization of other tissues because they can cause significant tissue ischemia via occlusion
down to the capillary level.
9. When performing an embolization procedure, why is it recommended always to place
a vascular sheath at the access site?
A vascular sheath assists in catheter exchanges during the procedure. More importantly, the sheath maintains vascular
access in the event the embolic agent clogs the delivery catheter, and the catheter needs to be removed.
10. What is postembolization syndrome?
Postembolization syndrome is an expected set of symptoms, including pain, fever, nausea, vomiting, and leukocytosis,
that patients may experience after an embolization. The cause is likely secondary to organ ischemia/infarction.
Prophylactic antibiotics to prevent superinfection of the ischemic tissue and pain control and antiemetic agents are
helpful in treating postembolization syndrome. The syndrome is transient and should resolve within 3 to 5 days after
the procedure.
11. How can nontarget embolization be minimized?
Meticulous pre-embolization diagnostic angiography can ensure proper selective catheterization of the desired vessel.
12. When performing an embolization procedure for an upper GI bleed, what information
from the endoscopy report is essential?
Because clinically significant upper GI bleeding may be intermittent or too slow to be identified angiographically,
arteriograms performed in this setting often display normal results. Empiric embolizations are commonly performed
even when arteriograms have normal results. Embolization of an arteriographically  normal vessel can be performed
safely because of the redundant collateral supply to the stomach and duodenum. Ischemic complications of such
embolizations are rare unless the patient has a compromised network of collaterals from previous surgery. Before
the procedure, it is necessary to know exactly where the patient is bleeding. If the source is duodenal, the gastroduodenal
artery is embolized. If the source is gastric, the left gastric artery is embolized.
13. Can a lower GI bleed be treated with empiric embolization?
The colon and small bowel lack the extensive collateral network present in the stomach and duodenum. Empiric
embolization of a vascular distribution would cause extensive ischemia and bowel necrosis. The approach to lower GI
bleeds is much different. To perform an embolization, the site of bleeding must be identified on the angiogram. Nuclear
medicine scans to detect bleeding are often performed before an arteriogram. These scans are noninvasive and can
detect intermittent bleeding and hemorrhage that is much slower than that which can be detected on an arteriogram.
If the nuclear medicine scan shows negative results, it is of virtually no value to perform an arteriogram. If the nuclear
medicine scan shows positive results, and the site of hemorrhage can be identified on the arteriogram, embolization can
be attempted.
14. In the setting of pelvic trauma or peripartum hemorrhage in a patient with an
unstable condition, is superselective embolization always indicated?
In emergent settings, with a patient with an unstable condition, the goal is efficient hemostasis and stabilization of the
patient s condition. Embolization of the entire internal iliac artery, if necessary, can be performed, usually with Gelfoam.
The time saved by avoiding further catheterization may be lifesaving. If the patient s condition is stable, selective
embolization may be performed to reduce ischemic complications (Fig. 33-1).
15. Name some clinical indications for angiography in patients with pelvic trauma.
The human pelvis represents a very large potential space, often able to accommodate 4 to 5 L of blood. Traumatic
diastasis of the symphysis pubis can double the effective potential space of the pelvis. Pelvic bleeding can be difficult
to control surgically. Splinting and external fixation are usually performed first to help reduce bleeding. Indications for
INTERVENTIONAL RADIOLOGY 243
A B
AB C
Figure 33-1. A, Digital subtraction angiography (DSA) after a gunshot wound reveals acute hemorrhage from a branch of the left deep
femoral artery (arrow). B, Delayed image from DSA prominently shows the hemorrhage (arrow). C, DSA after successful coil embolization of
the injured artery shows cessation of bleeding (arrow).
arteriography include open pelvic fracture, expanding pelvic hematoma, and transfusion requirement greater than 4 U
over 24 hours.
16. Is empiric embolization indicated in pelvic trauma?
In the setting of a pelvic fracture, bleeding may be from numerous sources. Venous bleeding is the most common
etiology. Bleeding from the periosteal surface of fractured bones is the next most common etiology, followed by arterial
hemorrhage. In the setting of an arteriogram with normal results, arterial embolization is not usually performed.
17. In bronchial artery embolization for hemoptysis, vigilance for which vessels is
imperative?
Anterior spinal arteries arising from bronchial arteries must be identified to prevent nontarget embolization and
subsequent paraplegia. Anterior spinal artery branches that arise from bronchial arteries have a classic  hairpin
appearance, traveling cranially for 1 cm or so before forming a loop and doubling back to travel caudally over the
midline of the spine.
18. Why should coils not be used in the bronchial arteries?
Life-threatening hemoptysis is often caused by chronic lung disease, such as sarcoidosis or cystic fibrosis. Because of
the chronic nature of the lung disease, hemoptysis is likely to recur. Embolization with coils makes future access to the
embolized vascular territory difficult, if not impossible. Particulate agents such as PVA are preferred.
19. Why is it necessary to embolize both sides of a pseudoaneurysm, aneurysm, or
arteriovenous fistula?
Significant reconstitution of flow via collaterals can occur and cause recurrence of the lesion. If only the
proximal feeding vessel to a pseudoaneurysm is embolized, flow may reverse in the outflow vessel and feed the
pseudoaneurysm. Embolizing both sides of a pseudoaneurysm, aneurysm, or arteriovenous fistula is called  embolizing
the front and back door of a lesion and is also sometimes needed when embolizing bleeding vessels.
20. What should always be placed when absolute ethanol is being used for renal artery
sclerosis?
An occlusion balloon must always be placed to prevent reflux of absolute ethanol into the aorta. The balloon should also
be distal to the origin of the adrenal and gonadal arteries because catecholamine release or gonadal ischemia can result
if ethanol is instilled into the respective arteries.
21. How is chemoembolization theorized to work?
Embolization of tumor vessels causes ischemia. This ischemia disables tumor cell membrane ion pumps and exocytosis
functions, and increases capillary permeability. As a result, there is increased intracellular accumulation and dwell time
of the concomitantly delivered chemotherapeutic agent, leading to increased tumor cell apoptosis.
244 EMBOLIZATION TECHNIQUES AND APPLICATIONS
Key Points: Embolization Techniques and Applications
1. Embolotherapy has various clinical applications, including control of bleeding; elimination of vascular
malformations; and tumor or organ ablation for curative, palliative, or preoperative purposes.
2. Postembolization syndrome is a transient and expected set of symptoms, including pain, fever, nausea,
vomiting, and leukocytosis, probably secondary to organ ischemia/infarction.
3. Meticulous pre-embolization diagnostic angiography to ensure appropriate selective catheterization of the
desired vessel is required to minimize nontarget embolization.
4. Embolization on both sides of a pseudoaneurysm, aneurysm, or arteriovenous fistula is necessary to prevent
reconstitution of flow via collaterals, which causes recurrence of the lesion.
5. Gas in the target organ within 3 to 5 days postembolization is thought to arise from tissue necrosis and does
not automatically equal infection.
22. What happens when the cystic artery is embolized during hepatic lesion
embolization/chemoembolization?
A transient chemical cholecystitis may result. This condition can be self-limited and may resolve with conservative
management. Incidental embolization of the cystic artery is believed to contribute to postembolization pain in patients
undergoing hepatic chemoembolization.
23. What happens if the left or right gastric artery is embolized during hepatic
chemoembolization?
Injecting chemotherapeutic agents directly into the bowel can cause irreversible gastric ischemia and eventual
necrosis. Meticulous attention to possible variants in gastric/bowel vascular supply is necessary when performing
pre-embolization diagnostic arteriograms.
24. What is the significance of gas in the target organ postembolization?
There is little significance. Gas is often present in the target organ after embolization and, as mentioned earlier, is
thought to arise from tissue necrosis. The presence of gas does not always indicate infection. Resorption of the gas may
take weeks.
25. What findings suggest that postembolization gas is due to infection?
Beyond 5 days postprocedure, when postembolization syndrome is expected to resolve, persistent fever, elevated serum
markers of inflammation (erythrocyte sedimentation rate, C-reactive protein), or a fluid level in the embolized area
suggests superinfection of the embolized tissue.
26. When is uterine artery embolization used in a nonemergent setting?
Uterine fibroids causing menorrhagia or pelvic pain can be treated effectively with bilateral uterine artery embolization.
Uterine artery embolization can be performed with permanent particles.
BIBLIOGRAPHY
[1] D.M. Coldwell, K.R. Stokes, W.F. Yakes, Embolotherapy: agents, clinical applications, and techniques, Radiographics 14 (1994) 623 643.
[2] M. Gee, M.C. Soulen, Chemoembolization for hepatic metastases, Tech. Vasc. Interv. Radiol. 5 (2002) 132 140.
[3] K.D. Murphy, Embolotherapy, in: D.S. Katz, K.R. Math, S.A. Groskin (Eds.), Radiology Secrets, Hanley & Belfus, Philadelphia, 1998,
pp. 502 510.
[4] J.P. Pelage, O. Le Dref, J. Mateo, et al., Life-threatening primary postpartum hemorrhage: treatment with emergency selective arterial
embolization, Radiology 208 (1998) 359 362.
[5] R.S. Salem, J.J. Borsa, R.J. Lewandowski, et al., Arterial embolotherapy, in: Proceedings of the Society of Interventional Radiology
Workshop, 29th Annual Meeting, 2004, pp. 237 249.
[6] I. Wells, Internal iliac artery embolization in the management of pelvic bleeding, Clin. Radiol. 51 (1996) 825 827.
[7] M. Wojtowycz, Handbook of Interventional Radiology and Angiography, second ed., Mosby, St Louis, 1995, pp. 229 251.