Liver Embolization

Embolization is a type of liver cancer treatment that involves the injection of substances directly into an artery in the liver to stop or reduce the blood supply to a liver tumor. This starves the tumor of oxygen and nutrients, which are delivered via the blood vessels, thereby destroying the cancer cells.

Together with ablation therapy, it is also known as a locoregional treatment or interventional procedure.

The liver is unique in that it has a dual blood supply. While normal, healthy liver cells receive their blood supply from branches of the portal vein, cancer cells in the liver are generally supplied by the hepatic artery. By blocking branches of the hepatic artery that feed the tumor, embolization can kill off cancer cells in the liver while leaving most healthy liver cells unharmed.

Embolization is typically used for tumors that cannot be removed surgically, either because they’re too large or because they’re in areas that make removal difficult. It is also an option for people with tumors that are too large to be treated with ablation (i.e., usually bigger than 5 cm across) but who still have adequate liver function. In some instances, embolization can be used together with ablation.

It should be noted that embolization can lower some of the blood flow to normal liver tissue, so it might not be a good treatment option if you have decompensated cirrhosis or poor hepatic function (e.g., ascites, encephalopathy, or elevated bilirubin).

Transarterial embolization (TAE)

Transarterial embolization (TAE) is also known as hepatic artery embolization (HAE) or bland embolization. During this minimally invasive procedure, a thin, flexible tube called a catheter is inserted into an artery through a small cut in the inner thigh (femoral access) or the wrist (radial access) and threaded up into the hepatic artery in your liver. A dye is typically injected into your bloodstream at this time, allowing your radiologist to observe the path of the catheter via a special type of X-ray called an angiography and guide its insertion into the hepatic artery.

Once the catheter is securely in place, microscopic particles composed of gelatin sponges or beads are injected into the hepatic artery to plug it up. These substances, which are known as embolic agents, block the blood supply to the liver tumor, eventually killing the cancer cells. This subsequently leads to shrinkage or necrosis of the tumor. When the procedure is completed, your doctor(s) will withdraw the catheter, after which the entry site is cleaned and covered with a dressing.

What happens to the plug depends on the type of embolic agents used. Some embolic agents are designed to gradually break down and/or be absorbed by your body. Others, especially those that are not biodegradable or bioresorbable, may remain in the treated area. Known as permanent embolics, these agents can become encapsulated by scar tissue, incorporated into nearby tissues or carried away to smaller vessels where they are lodged.

The use of permanent embolics in TAE is generally considered safe and effective when performed by trained and experienced interventional radiologists. However, as with any medical procedure, there are potential risks and complications associated with TAE using permanent embolics. These include:

• Ischemia: If the embolization is too extensive, it could potentially lead to damage of healthy liver tissue due to ischemia.
• Reperfusion injury: In some cases of TAE, blood flow may be restored after a certain period of ischemia. This can lead to inflammation and additional tissue damage, known as reperfusion injury.
• Non-target embolization: There is a risk of embolic material traveling to other areas and causing blockages in vessels that are not intended for treatment. This could potentially affect healthy liver tissue and liver function.
• Other post-procedural complications: these can include liver abscess formation or injury to the bile ducts (biliary necrosis), as the bile ducts rely solely on the hepatic artery for blood supply.

More common side effects are pain and nausea after the treatment, which are usually self-limited. Therefore, it is vital that you discuss the potential risks and benefits of TAE with your doctors before opting for the procedure.

Transarterial chemoembolization (TACE)

Transarterial chemoembolization (TACE), also known as hepatic artery chemoembolization (HACE), combines TAE with chemotherapy. This procedure is usually done by delivering chemotherapy through the catheter and directly into the artery, just before it is plugged with an embolic agent.

Besides stopping the tumor’s blood supply, this procedure delivers a very high concentration of chemotherapeutic agents to the tumor, which can destroy the cancer cells directly. The injection of embolic agents also traps the chemotherapeutics in the tumor for several weeks, allowing their cancer-killing effects to last for a prolonged period of time. Since this therapy is delivered solely to the liver tumor and does not travel through your bloodstream, normal, healthy tissue is spared, thereby lowering the occurrence of side effects.

TACE is typically the first type of embolization technique used for large liver tumors that cannot be treated with surgery or ablation.

Drug-eluting bead chemoembolization (DEB-TACE)

Drug-eluting bead chemoembolization is a specific type of TACE that uses microspheres (beads) that are pre-loaded with chemotherapy drugs. Unlike conventional TACE, where the drug is injected first, followed by a separate embolic agent, in DEB-TACE, the beads serve a dual function: they mechanically occlude the blood vessel to stop flow and simultaneously provide a controlled, sustained release of chemotherapy directly into the tumor. This allows for a higher intratumoral drug concentration with lower systemic toxicity compared to conventional TACE.

Mitomycin C, cisplatin and doxorubicin are the most common chemotherapy drugs used for TACE or DEB-TACE.

Transarterial radioembolization (TARE)

Transarterial radioembolization (TARE), also known as selective internal radiation therapy (SIRT), is a minimally invasive procedure that combines embolization and radiotherapy. Tiny radioactive beads, known as microspheres, attached with a radioactive isotope (yttrium-90), are injected into the hepatic artery. Unlike TAE or TACE, the primary mechanism of TARE is not the blockage of blood flow (ischemia), but rather the delivery of high-dose internal radiation. The microspheres lodge in the tiny blood vessels within the tumor, emitting radiation from the inside out to destroy cancer cells while minimizing the embolic effect on the surrounding hepatic artery flow. The beta radiation emitted by the isotope has a limited tissue penetration (average of 2.5 mm). This property ensures that the treating dose is confined to the tumor, thereby sparing the normal liver.

Embolization is generally an outpatient procedure that lasts for two to three hours, and you can usually go home on the same day. However, in some instances, you may be required to stay in the hospital overnight for observation if you’re experiencing pain or nausea after the procedure.

Recovery afterwards can take up to six weeks, and common side effects include:

• Pain at the entry site or abdominal region
• Fever
• Nausea and/or vomiting

Collectively, these are called post-embolization syndrome, which usually lasts from a few days to a week. Your doctor(s) will provide you with painkillers and anti-sickness medication to manage them.

Other side effects and complications include:

• Fatigue
• Bruising at the entry site
• Liver infection
• Blood clots in the blood vessels surrounding the liver

If these problems grow more severe or if they do not resolve, do inform your doctor(s).

Please be assured that follow-up imaging tests, such as computed tomography (CT) or magnetic resonance imaging (MRI) scans, will be performed to examine your response to these embolization procedures and to monitor the treated tissues over time.