Hepatic Chemoembolization Imaging 

Hepatocellular carcinoma (HCC) is the most common primary liver tumor worldwide, and its incidence is rising. Most HCCs are associated with cirrhosis. The risk of developing HCC appears to be related to the degree of activity of cirrhosis. The risk is high in patients with macronodular cirrhosis secondary to hemochromatosis and lower in those with alcoholic micronodular cirrhosis. Surgery offers the best prospect of cure, but the resectability of HCC is low.

Depending on the primary site, 30-70% of patients who die of cancer have liver metastasis at autopsy. The most common cause of death from colorectal cancer is liver metastasis.

Key predictors of tumor response after chemoembolization on unresectable HCC include the tumor's size, vascularity, and number, and portal vein invasion. Factors associated with poor prognosis for overall patient survival include Child-Pugh class B or C, tumor size ≥4 cm, 5 or more tumors, portal vein invasion, and an alpha fetoprotein (AFP) level >83 ng/mL.^[1]

Conventional and drug-eluting bead chemoembolization have been found to have a limited impact on liver function, and tumor response is not dependent on type of embolization used.^[2]

Diagnostic imaging depicts not only the primary hepatic disease but also ascites, lymph node metastases, and thrombosis of portal or hepatic veins. Confirming portal vein patency is important because portal vein thrombosis is a relative contraindication to chemoembolization.^{[3, 4]} If portal flow via collateral vessels remains hepatopetal, embolization may be better tolerated. Imaging also plays an important role in evaluating the effectiveness of interventional therapy.

An axial computed tomography (CT) scan of an HCC is seen below.

Preferred examination

The imaging strategy in HCC depends on the clinical question to be answered and the treatment options available.^[5]

Angiography is an essential part of the workup performed prior to embolization or chemoembolization, although most centers proceed to the embolization procedure if no contraindications are present.

In patients with a known primary malignancy, such as colorectal cancer or islet cell tumors, an initial investigation includes an ultrasonographic examination followed by spiral or multisection, 3-phase, contrast-enhanced CT scanning.

Contrast-enhanced sonography is useful in determining the differences between the grades of HCCs. Using auto-tracking contrast quantification software, the time to peak, contrast-enhanced time, and wash-out time were longer for well-differentiated hepatocellular lesions and the enhancement slope and clearance slope were lower than that of moderately to poorly differentiated carcinomas.^[6]

Magnetic resonance imaging (MRI) and radionuclide scanning are useful in confirming the diagnosis, particularly the diagnosis of benign lesions, such as hemangiomas and focal nodular hyperplasia. These lesions are increasingly encountered in the setting of malignant disease. The multiplanar capability of MRI is particularly helpful in determining the exact anatomic location of the lesions. In the setting of HCC, a protocol similar to that used for liver metastasis is performed.

A review by Rempp and associates suggested that radiofrequency ablation should be used in patients with early-stage HCC with up to 3 lesions with a tumor diameter of ≤ 3 cm and for patients with nonresectable liver metastasis.^[10]

Postprocedural imaging

Follow-up CT scans are obtained approximately 10-14 days after chemoembolization. An early scan may be acquired if complications, such as nontarget embolization, are suspected.

Because the chemotherapeutic agent is mixed with lipiodol, CT scans of a tumor reveal dense opacification associated with necrosis (see the image below).

Along with nontarget embolization, CT scans also demonstrate such complications as the development of ascites and pleural effusions. When only polyvinyl alcohol embolization is performed, as in cases of hepatic carcinoid, postembolization CT scans demonstrate only tumor necrosis.^[7]

In patients with hepatocellular carcinoma (HCC), if the embolization procedure is successful, the postprocedural CT scan will show a lipiodol uptake of greater than 50% in necrotic tumor. In these cases, the embolization is repeated in 6-8 weeks. If the lipiodol uptake is less than 50%, the authors repeat the CT scan in 6-8 weeks.^[8]

As previously mentioned, MRI and radionuclide scanning are useful in confirming a diagnosis, particularly the diagnosis of benign lesions, such as hemangiomas and focal nodular hyperplasia. These lesions are increasingly encountered in the setting of malignant disease. The multiplanar capability of MRI is particularly helpful in determining the exact anatomic location of the lesions. In the setting of hepatocellular carcinoma, a protocol similar to that used for liver metastasis is performed.

Angiography is an essential part of the workup performed prior to embolization or chemoembolization, although most centers proceed to the embolization procedure if no contraindications are present. Angiography is usually performed by placing a 5F to 6F catheter through a sheath via the right or left femoral artery. The catheter should be able to accept the insertion of a 3F coaxial microcatheter. A celiac-axis and superior mesenteric angiogram is first obtained to identify common variations in the blood supply to the liver and to check for patency of the portal vein.

Angiograms obtained prior to and after chemoembolization are seen below.

Embolization of parasitized extrahepatic arteries (EHAs) to reestablish intrahepatic arterial inflow to hepatic tumors was found to be safe and effective in a retrospective analysis of 201 patients.^[9] The procedure successfully delivered yttrium-90 microspheres to tumors previously perfused by parasitized EHAs.