Chemoembolization involves super-selective, intra-arterial chemotherapy delivery in conjunction with subsequent or simultaneous particle embolization. The rationale for chemoembolization for primary and metastatic tumors of the liver is based on anatomic studies that demonstrated that most hepatic tumors depend upon hepatic arterial blood supply (up to 95%) for growth in contrast to the normal liver parenchyma that receives the majority of its blood supply via the portal vein (only ~20% from the hepatic artery).35 Hepatic artery embolization causes more ischemia to the liver tumor while the remaining normal hepatic parenchyma obtains sufficient oxygenation from the portal venous blood supply to remain viable. Furthermore, pharmacological studies indicate that intra-arterial delivery of chemotherapy results in a 10- to 50-fold increase in intra-tumoral drug concentrations when compared to systemic intravenous chemotherapy administration in certain locations.36
Particle embolization may cause tumor necrosis but also has a synergistic effect with the intra-arterial delivery of chemotherapy because the ischemia it induces in tumor cells inhibits the excretion of chemotherapy resulting in a higher concentration of drug accumulation within the cell. This effect maximizes cell death while minimizing systemic toxicity. This procedure is most commonly used in the treatment of diffuse hepatocellular carcinoma or metastatic liver disease in humans.
In addition, when used within the liver, the chemotherapy is mixed with a carrier agent, Ethiodol (Savage Laboratories, Melville, NY). This iodized oily substance supplies radiographic contrast to the chemotherapy as well as acting as a tumor localizer and embolic agent. Hepatic tumors lack Kupfer cells which are important for metabolizing oily substances (lipid) in normal hepatic parenchyma. Therefore, the Ethiodol and accompanying chemotherapy are concentrated within the liver tumor rather than the surrounding healthy hepatic parenchyma.37 Chemoembolization is currently being evaluated in veterinary patients with non-resectable or metastatic liver tumors as well as other locations throughout the body of both dogs and cats. (Figure 12)
|Figure 12. Complete hepatic chemoembolization in animals with diffuse or metastatic liver disease. (A) DSA of hepatic artery (HA) in a dog before chemoembolization. Note hepatic artery branches to liver parenchyma and patent gastroduodenal artery (GDA). (B) Same patient post-chemoembolization DSA demonstrating patent GDA but lack of perfusion to the hepatic artery branches following the procedure. (C) Axial CT angiogram of a cat with a large hepatic neuroendocrine tumor (black arrows) and metastatic lesion in adjacent lobe (black arrowheads). (D) Non-contrast enhanced, axial CT scan post-chemoembolization of the majority of the liver demonstrating increased uptake of chemotherapy mixture within primary (large *) and metastatic (small *) tumor as compared to normal liver parenchyma, even when performed non-selectively.