Embolization

Embolization
Embolization
	Micrograph of embolic material in the artery of a kidney. The kidney was surgically removed because of cancer. H&E stain.
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Last updated December 29, 2024

Embolization refers to the passage and lodging of an embolus within the bloodstream. It may be of natural origin (pathological), in which sense it is also called embolism, for example a pulmonary embolism; or it may be artificially induced (therapeutic), as a hemostatic treatment for bleeding or as a treatment for some types of cancer by deliberately blocking blood vessels to starve the tumor cells.

In the cancer management application, the embolus, besides blocking the blood supply to the tumor, also often includes an ingredient to attack the tumor chemically or with irradiation. When it bears a chemotherapy drug, the process is called chemoembolization. Transcatheter arterial chemoembolization (TACE) is the usual form. When the embolus bears a radiopharmaceutical for unsealed source radiotherapy, the process is called radioembolization or selective internal radiation therapy (SIRT).

Uses

Embolization involves the selective occlusion of blood vessels by purposely introducing emboli, in other words deliberately blocking a blood vessel. Embolization is used to treat a wide variety of conditions affecting different organs of the human body.

Embolization is commonly used to treat active arterial bleeding. Embolization is rarely used to treat venous bleeding as venous bleeding can stop on its own or with packing or compression.^[1]^[2]

Bleeding

The treatment is used to occlude:

Recurrent coughing up of blood
Cerebral aneurysm ^[3]
Gastrointestinal bleeding
Nosebleed
Varicocele
Primary post-partum bleeding ^[4]
Surgical bleeding ^[5]
Traumatic bleeding such as splenic rupture or pelvic fracture

Growths

The treatment is used to slow or stop blood supply thus reducing the size of the tumour:

Kidney lesions
Liver lesions, typically hepatocellular carcinoma (HCC). Treated either by particle infarction or transcatheter arterial chemoembolization (TACE).
Uterine fibroids
Arteriovenous malformations (AVMs)
Arteriovenous fistula
Juvenile Nasopharyngeal Angiofibroma

Malignant hypertension

It could be useful for managing malignant hypertension due to end stage kidney failure.^[6]

Other

Portal vein embolization prior to liver resection.^[7]

Technique

First developed by Sadek Hilal in 1968, embolization is a minimally invasive surgical technique.^[8] The purpose is to prevent blood flow to an area of the body, which can effectively shrink a tumor or block an aneurysm.

The procedure is carried out as an endovascular procedure by an interventional radiologist in an interventional suite. It is common for most patients to have the treatment carried out with little or no sedation, although this depends largely on the organ to be embolized. Patients who undergo cerebral embolization or portal vein embolization are usually given a general anesthetic.

Access to the organ in question is acquired by means of a guidewire and catheter(s). Depending on the organ this can be very difficult and time-consuming. The position of the correct artery or vein supplying the pathology in question is located by digital subtraction angiography (DSA). These images are then used as a map for the radiologist to gain access to the correct vessel by selecting an appropriate catheter and or wire, depending on the 'shape' of the surrounding anatomy.

Once in place, the treatment can begin. The artificial embolus used is usually one of the following:

Coils: Guglielmi Detachable Coil or Hydrocoil
Particles
Foam
Plug
Microspheres or Beads

Once the artificial emboli have been successfully introduced, another set of DSA images are taken to confirm a successful deployment.

Agents

Liquid embolic agents – Used for AVM, these agents can flow through complex vascular structures so the surgeon does not need to target the catheter to every single vessel.

Butyl cyanoacrylate (NBCA) – This material is approved by FDA in 2000 for embolisation of cerebral arteriovenous malformation. When exposed to an environment containing anions such as blood or water, it polymerises quickly. Catheters should be flushed with dextrose 5% to prevent premature polymerisation within the catheter. NBCA completely occludes vessels and is permanent. However, the polymerisation can spread distally or proximally of the intended location.^[9]
ethiodol – Made from iodine and poppyseed oil, this is a highly viscous agent. It is usually used for chemoembolizations, especially for hepatomas, since these tumors absorb iodine. The half life is five days, so it only temporarily embolizes vessels.
Ethylene Vinyl Alcohol Copolymer, soluted in Dimethyl-Sulfoxide (DMSO) under the trade name Onyx. Depending on the desired character of the liquid, the concentration can be varied: For example, 6% EVOH (trade name Onyx 18) or 8% EVOH (trade name Onyx 34). Micronized tantalum powder is added in order to maintain Radiopacity.

Sclerosing agents – These will harden the endothelial lining of vessels. They require more time to react than the liquid embolic agents. Therefore, they cannot be used for large or high-flow vessels.

ethanol – This permanent agent is very good for treating AVM. The alcohol does need some time to denature proteins of the endothelium and activate the coagulation system to cause a blood clot. Therefore, some surgeons will use a balloon occlusion catheter to stop the blood flow and allow time for ethanol to work. Ethanol is toxic to the system in large quantities and may cause compartment syndrome. In addition, the injections are painful.
ethanolamine oleate – This permanent agent is used for sclerosing esophageal varices. It contains 2% benzyl alcohol, so it is less painful than ethanol. However it does cause hemolysis and kidney failure in large doses.
sotradecol – This agent is used for superficial lower extremity varicose veins. It has been around for a very long time and is a proven remedy. However, it does cause hyperpigmentation of the region in 30% of patients. It is less painful than ethanol.

Particulate embolic agents – These are only used for precapillary arterioles or small arteries. These are also very good for AVM deep within the body. The disadvantage is that they are not easily targeted in the vessel. None of these are radioopaque, so they are difficult to view with radiologic imaging unless they are soaked in contrast prior to injection.

Gelfoam hemostasis – It is made of animal-derived gelatin and is shaped into a sponge-like form. It can be made into a paste applied over a surface or made into small particles that can be injected via syringe.^[10] Gelfoam sheets can be cut into 1–3 mm pledgets, mixed with contrast materials for embolization. Gelfoam temporarily occludes blood vessels for 3 to 6 weeks. Each particle sized from 10 to 100 micrometers.^[11] Gelfoam use is associated with small risk of infection due to trapped air bubbles.^[11]
polyvinyl alcohol (PVA) – These are permanent agents. They are tiny balls 50–1200 um in size. The particles are not meant to mechanically occlude a vessel. Instead they cause an inflammatory reaction. Unfortunately, they have a tendency to clump together since the balls are not perfectly round. The clump can separate a few days later, failing as an embolic agent.
Embolization microspheres – These are superior permanent or resorbable particulate embolic agents available in different well-calibrated size ranges for precise occlusion. Embolization microspheres may comprise additional functionality such as drug loading and elution capability, specific mechanical properties, imageability or radioactivity

Mechanical occlusion devices – These fit in all vessels. They also have the advantage of accuracy of location; they are deployed exactly where the catheter ends.

coils – These are used for AVF, aneurysms, or trauma. They are very good for fast-flowing vessels because they immediately clot the vessel. They are made from platinum or stainless steel. They induce clots due to the Dacron wool tails around the wire. The coil itself will not cause mechanical occlusion. Since it is made of metal, it is easily seen in radiographic images. The disadvantage is that large coils can disrupt the radiographic image. The coil may also lose its shape if the catheter is kinked. Also, there is a small risk of dislodging from the deployed location.
detachable balloon – Treats AVF and aneurysms. These balloons are simply implanted in a target vessel, then filled with saline through a one-way valve. The blood stops and endothelium grows around the balloon until the vessel fibroses. The balloon may be hypertonic relative to blood and hence rupture and fail, or it may be hypotonic and shrink, migrating to a new location.

Advantages

Minimally invasive
No scarring
Minimal risk of infection
No or rare use of general anesthetic
Faster recovery time
High success rate compared to other procedures
Preserves fertility and anatomical integrity

Disadvantages

User dependent success rate
Risk of emboli reaching healthy tissue potentially causing gastric, stomach or duodenal ulcers.^[12] There are methods, techniques and devices that decrease the occurrence of this type of adverse side effect.^[13]
Not suitable for everyone
Recurrence more likely

Related Research Articles

An arteriovenous malformation (AVM) is an abnormal connection between arteries and veins, bypassing the capillary system. Usually congenital, this vascular anomaly is widely known because of its occurrence in the central nervous system, but can appear anywhere in the body. The symptoms of AVMs can range from none at all to intense pain or bleeding, and they can lead to other serious medical problems.

An intracranial aneurysm, also known as a cerebral aneurysm, is a cerebrovascular disorder characterized by a localized dilation or ballooning of a blood vessel in the brain due to a weakness in the vessel wall. These aneurysms can occur in any part of the brain but are most commonly found in the arteries of the cerebral arterial circle. The risk of rupture varies with the size and location of the aneurysm, with those in the posterior circulation being more prone to rupture.

Angiography or arteriography is a medical imaging technique used to visualize the inside, or lumen, of blood vessels and organs of the body, with particular interest in the arteries, veins, and the heart chambers. Modern angiography is performed by injecting a radio-opaque contrast agent into the blood vessel and imaging using X-ray based techniques such as fluoroscopy. With time-of-flight (TOF) magnetic ressonance it is no longer necessary to use a contrast.

Interventional radiology (IR) is a medical specialty that performs various minimally-invasive procedures using medical imaging guidance, such as x-ray fluoroscopy, computed tomography, magnetic resonance imaging, or ultrasound. IR performs both diagnostic and therapeutic procedures through very small incisions or body orifices. Diagnostic IR procedures are those intended to help make a diagnosis or guide further medical treatment, and include image-guided biopsy of a tumor or injection of an imaging contrast agent into a hollow structure, such as a blood vessel or a duct. By contrast, therapeutic IR procedures provide direct treatment—they include catheter-based medicine delivery, medical device placement, and angioplasty of narrowed structures.

Hereditary hemorrhagic telangiectasia (HHT), also known as Osler–Weber–Rendu disease and Osler–Weber–Rendu syndrome, is a rare autosomal dominant genetic disorder that leads to abnormal blood vessel formation in the skin, mucous membranes, and often in organs such as the lungs, liver, and brain.

Cerebral angiography is a form of angiography which provides images of blood vessels in and around the brain, thereby allowing detection of abnormalities such as arteriovenous malformations and aneurysms. It was pioneered in 1927 by the Portuguese neurologist Egas Moniz at the University of Lisbon, who also helped develop thorotrast for use in the procedure.

Transcatheter arterial chemoembolization (TACE) is a minimally invasive procedure performed in interventional radiology to restrict a tumor's blood supply. Small embolic particles coated with chemotherapeutic drugs are injected selectively through a catheter into an artery directly supplying the tumor. These particles both block the blood supply and induce cytotoxicity, attacking the tumor in several ways.

<span class="mw-page-title-main">Uterine artery embolization</span> Medical intervention

Uterine artery embolization is a procedure in which an interventional radiologist uses a catheter to deliver small particles that block the blood supply to the uterine body. The procedure is primarily done for the treatment of uterine fibroids and adenomyosis. Compared to surgical treatment for fibroids such as a hysterectomy, in which a woman's uterus is removed, uterine artery embolization may be beneficial in women who wish to retain their uterus. Other reasons for uterine artery embolization are postpartum hemorrhage and uterine arteriovenous malformations.

<span class="mw-page-title-main">Selective internal radiation therapy</span>

Selective internal radiation therapy (SIRT), also known as transarterial radioembolization (TARE), radioembolization or intra-arterial microbrachytherapy is a form of radionuclide therapy used in interventional radiology to treat cancer. It is generally for selected patients with surgically unresectable cancers, especially hepatocellular carcinoma or metastasis to the liver. The treatment involves injecting tiny microspheres of radioactive material into the arteries that supply the tumor, where the spheres lodge in the small vessels of the tumor. Because this treatment combines radiotherapy with embolization, it is also called radioembolization. The chemotherapeutic analogue is called chemoembolization, of which transcatheter arterial chemoembolization (TACE) is the usual form.

Acute limb ischaemia (ALI) occurs when there is a sudden lack of blood flow to a limb within 14 days of symptoms onset. On the other hand, when the symptoms exceed 14 days, it is called critical limb ischemia (CLI). CLI is the end stage of peripheral vascular disease where there is still some collateral circulation that bring some blood flow to the distal parts of the limbs. While limbs in both acute and chronic limb ischemia may be pulseless, a chronically ischemic limb is typically warm and pink due to a well-developed collateral artery network and does not need emergency intervention to avoid limb loss, whereas ALI is a vascular emergency.

Interventional neuroradiology (INR) also known as neurointerventional surgery (NIS), endovascular therapy (EVT), endovascular neurosurgery, and interventional neurology is a medical subspecialty of neurosurgery, neuroradiology, intervention radiology and neurology specializing in minimally invasive image-based technologies and procedures used in diagnosis and treatment of diseases of the head, neck, and spine.

Hepatic artery embolization, also known as trans-arterial embolization (TAE), is one of the several therapeutic methods to treat primary liver tumors or metastases to the liver. The embolization therapy can reduce the size of the tumor, and decrease the tumor's impact such its hormone production, effectively decreasing symptoms. The treatment was initially developed in the early 1970s. The several types of hepatic artery treatments are based on the observation that tumor cells get nearly all their nutrients from the hepatic artery, while the normal cells of the liver get about 70-80 percent of their nutrients and 50% their oxygen supply from the portal vein, and thus can survive with the hepatic artery effectively blocked. In practice, hepatic artery embolization occludes the blood flow to the tumors, achieving significant tumor shrinkage in over 80% of people. Shrinkage rates vary.

Interventional oncology is a subspecialty field of interventional radiology that deals with the diagnosis and treatment of cancer and cancer-related problems using targeted minimally invasive procedures performed under image guidance. Interventional oncology has developed to a separate pillar of modern oncology and it employs X-ray, ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI) to help guide miniaturized instruments to allow targeted and precise treatment of solid tumours located in various organs of the human body, including but not limited to the liver, kidneys, lungs, and bones. Interventional oncology treatments are routinely carried out by interventional radiologists in appropriate settings and facilities.

Portal vein embolization (PVE) is a preoperative procedure performed in interventional radiology to initiate hypertrophy of the anticipated future liver remnant a couple weeks prior to a major liver resection procedure. The procedure involves injecting the right or left portal vein with embolic material to occlude portal blood flow. By occluding the blood flow to areas of the liver that will be resected away, the blood is diverted to healthy parts of the liver and induces hyperplasia. This may allow for a more extensive resection or stage bilateral resections that would otherwise be contraindicated resulting in better oncological treatment outcomes.

Endovascular and hybrid trauma and bleeding management is a new and rapidly evolving concept within medical healthcare and endovascular resuscitation. It involves early multidisciplinary evaluation and management of hemodynamically unstable patients with traumatic injuries as well as being a bridge to definitive treatment. It has recently been shown that the EVTM concept may also be applied to non-traumatic hemodynamically unstable patients.

Transarterial bland embolization is a catheter-based tumor treatment of the liver. In this procedure, embolizing agents can be delivered through the tumor's feeding artery in order to completely occlude the tumor's blood supply. The anti-tumor effects are solely based on tumor ischemia and infarction of tumor tissue, as no chemotherapeutic agents are administered. The rationale for the use of bland embolization for hepatocellular carcinoma (HCC) and/or other hyper-vascular tumors is based on the fact that a normal liver receives a dual blood supply from the hepatic artery (25%) and the portal vein (75%). As the tumor grows, it becomes increasingly dependent on the hepatic artery for blood supply. Once a tumor nodule reaches a diameter of 2 cm or more, most of the blood supply is derived from the hepatic artery. Therefore, bland embolization and transarterial chemoembolization (TACE) consist of the selective angiographic occlusion of the tumor arterial blood supply with a variety of embolizing agents, with or without the precedence of local chemotherapy infusion. The occlusion by embolic particles results in tumor hypoxia and necrosis, without affecting the normal hepatic parenchyma.

Segmental arterial mediolysis (SAM) is a rare disorder of the arteries characterized by the development of aneurysms, blood clots, narrowing of the arteries (stenoses), and blood collections (hematomas) in the affected distribution.

Bronchial artery embolization is a treatment for hemoptysis, abbreviated as BAE. It is a kind of catheter intervention to control hemoptysis by embolizing the bronchial artery, which is a bleeding source. Embolic agents are particulate embolic material such as gelatin sponge or polyvinyl alcohol (PVA), and liquid embolic material such as NBCA, or metallic coils.

<span class="mw-page-title-main">Arterial occlusion</span>

Arterial occlusion is a condition involving partial or complete blockage of blood flow through an artery. Arteries are blood vessels that carry oxygenated blood to body tissues. An occlusion of arteries disrupts oxygen and blood supply to tissues, leading to ischemia. Depending on the extent of ischemia, symptoms of arterial occlusion range from simple soreness and pain that can be relieved with rest, to a lack of sensation or paralysis that could require amputation.

Hemorrhoidal artery embolization is a non-surgical treatment of internal hemorrhoids.

References

↑ Lopera JE (March 2010). "Embolization in trauma: principles and techniques". Seminars in Interventional Radiology. 27 (1): 14–28. doi:10.1055/s-0030-1247885. PMC 3036510 . PMID 21359011.
↑ Anchala PR, Resnick SA (December 2010). "Treatment of postoperative hemorrhage with venous embolization". Journal of Vascular and Interventional Radiology. 21 (12): 1915–7. doi:10.1016/j.jvir.2010.09.012. PMID 21035357.
↑ Jiang B, Paff M, Colby GP, Coon AL, Lin LM (September 2016). "Cerebral aneurysm treatment: modern neurovascular techniques". Stroke and Vascular Neurology. 1 (3): 93–100. doi:10.1136/svn-2016-000027. PMC 5435202 . PMID 28959469.
↑ Chauleur C, Fanget C, Tourne G, Levy R, Larchez C, Seffert P (July 2008). "Serious primary post-partum hemorrhage, arterial embolization and future fertility: a retrospective study of 46 cases". Human Reproduction. 23 (7): 1553–1559. doi: 10.1093/humrep/den122 . PMID 18460450.
↑ Whittingham-Jones P, Baloch I, Miles J, Ferris B (2010). "Persistent haemarthrosis following total knee arthroplasty caused by unrecognised arterial injury". Grand Rounds. 10: 51–54. doi:10.1102/1470-5206.2010.0010 (inactive November 1, 2024). Archived from the original on October 24, 2010.{{cite journal}}: CS1 maint: DOI inactive as of November 2024 (link)
↑ Alhamid N, Alterky H, Othman MI (January 2013). "Renal artery embolization for managing uncontrolled hypertension in a kidney transplant candidate". Avicenna Journal of Medicine. 3 (1): 23–25. doi: 10.4103/2231-0770.112791 . PMC 3752858 . PMID 23984264.
↑ Madoff DC, Hicks ME, Vauthey JN, Charnsangavej C, Morello FA, Ahrar K, et al. (2002). "Transhepatic portal vein embolization: anatomy, indications, and technical considerations". Radiographics. 22 (5): 1063–1076. doi: 10.1148/radiographics.22.5.g02se161063 . PMID 12235336.
↑ Hilal SK and Michelsen JW. "Therapeutic percutaneous embolization for extra-axial vascular lesions of the head, neck, and spine." J Neurosurg. 1975 Sep;43(3):275-87.
↑ Vaidya S, Tozer KR, Chen J (September 2008). "An overview of embolic agents". Seminars in Interventional Radiology. 25 (3): 204–215. doi:10.1055/s-0028-1085930. PMC 3036437 . PMID 21326511.
↑ Heller HT, Walker BS, Sadow CA, Frates MC (February 2017). "Imaging appearance of topical haemostatic agents: pictorial review". The British Journal of Radiology. 90 (1070): 20160664. doi:10.1259/bjr.20160664. PMC 5685128 . PMID 27936887.
1 2 Medsinge A, Zajko A, Orons P, Amesur N, Santos E (October 2014). "A case-based approach to common embolization agents used in vascular interventional radiology". AJR. American Journal of Roentgenology. 203 (4): 699–708. doi:10.2214/AJR.14.12480. PMID 25247933.
↑ Carretero C, Munoz-Navas M, Betes M, Angos R, Subtil JC, Fernandez-Urien I, et al. (June 2007). "Gastroduodenal injury after radioembolization of hepatic tumors". The American Journal of Gastroenterology. 102 (6): 1216–1220. doi:10.1111/j.1572-0241.2007.01172.x. hdl: 10171/27487 . PMID 17355414. S2CID 121385.
↑ Arepally A, Chomas J, Kraitchman D, Hong K (April 2013). "Quantification and reduction of reflux during embolotherapy using an antireflux catheter and tantalum microspheres: ex vivo analysis". Journal of Vascular and Interventional Radiology. 24 (4): 575–580. doi:10.1016/j.jvir.2012.12.018. PMID 23462064.

External links

eMedicine: Embolization

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[pmid21359011-1] Lopera JE (March 2010). "Embolization in trauma: principles and techniques". Seminars in Interventional Radiology. 27 (1): 14–28. doi:10.1055/s-0030-1247885. PMC 3036510 . PMID 21359011.

[pmid21035357-2] Anchala PR, Resnick SA (December 2010). "Treatment of postoperative hemorrhage with venous embolization". Journal of Vascular and Interventional Radiology. 21 (12): 1915–7. doi:10.1016/j.jvir.2010.09.012. PMID 21035357.

[pmid28959469-3] Jiang B, Paff M, Colby GP, Coon AL, Lin LM (September 2016). "Cerebral aneurysm treatment: modern neurovascular techniques". Stroke and Vascular Neurology. 1 (3): 93–100. doi:10.1136/svn-2016-000027. PMC 5435202 . PMID 28959469.

[pmid18460450-4] Chauleur C, Fanget C, Tourne G, Levy R, Larchez C, Seffert P (July 2008). "Serious primary post-partum hemorrhage, arterial embolization and future fertility: a retrospective study of 46 cases". Human Reproduction. 23 (7): 1553–1559. doi: 10.1093/humrep/den122 . PMID 18460450.

[Persistent_haemarthrosis_GR2010-5] Whittingham-Jones P, Baloch I, Miles J, Ferris B (2010). "Persistent haemarthrosis following total knee arthroplasty caused by unrecognised arterial injury". Grand Rounds. 10: 51–54. doi:10.1102/1470-5206.2010.0010 (inactive November 1, 2024). Archived from the original on October 24, 2010.{{cite journal}}: CS1 maint: DOI inactive as of November 2024 (link)

[pmid23984264-6] Alhamid N, Alterky H, Othman MI (January 2013). "Renal artery embolization for managing uncontrolled hypertension in a kidney transplant candidate". Avicenna Journal of Medicine. 3 (1): 23–25. doi: 10.4103/2231-0770.112791 . PMC 3752858 . PMID 23984264.

[pmid12235336-7] Madoff DC, Hicks ME, Vauthey JN, Charnsangavej C, Morello FA, Ahrar K, et al. (2002). "Transhepatic portal vein embolization: anatomy, indications, and technical considerations". Radiographics. 22 (5): 1063–1076. doi: 10.1148/radiographics.22.5.g02se161063 . PMID 12235336.

[8] Hilal SK and Michelsen JW. "Therapeutic percutaneous embolization for extra-axial vascular lesions of the head, neck, and spine." J Neurosurg. 1975 Sep;43(3):275-87.

[9] Vaidya S, Tozer KR, Chen J (September 2008). "An overview of embolic agents". Seminars in Interventional Radiology. 25 (3): 204–215. doi:10.1055/s-0028-1085930. PMC 3036437 . PMID 21326511.

[pmid27936887-10] Heller HT, Walker BS, Sadow CA, Frates MC (February 2017). "Imaging appearance of topical haemostatic agents: pictorial review". The British Journal of Radiology. 90 (1070): 20160664. doi:10.1259/bjr.20160664. PMC 5685128 . PMID 27936887.

[pmid25247933-11] 1 2 Medsinge A, Zajko A, Orons P, Amesur N, Santos E (October 2014). "A case-based approach to common embolization agents used in vascular interventional radiology". AJR. American Journal of Roentgenology. 203 (4): 699–708. doi:10.2214/AJR.14.12480. PMID 25247933.

[pmid17355414-12] Carretero C, Munoz-Navas M, Betes M, Angos R, Subtil JC, Fernandez-Urien I, et al. (June 2007). "Gastroduodenal injury after radioembolization of hepatic tumors". The American Journal of Gastroenterology. 102 (6): 1216–1220. doi:10.1111/j.1572-0241.2007.01172.x. hdl: 10171/27487 . PMID 17355414. S2CID 121385.

[pmid23462064-13] Arepally A, Chomas J, Kraitchman D, Hong K (April 2013). "Quantification and reduction of reflux during embolotherapy using an antireflux catheter and tantalum microspheres: ex vivo analysis". Journal of Vascular and Interventional Radiology. 24 (4): 575–580. doi:10.1016/j.jvir.2012.12.018. PMID 23462064.

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