After hepatoblastoma, hepatocellular carcinoma (HCC) account for the majority of malignant tumors of the liver in patients between 5 and 15 years. Males are affected more than females, and 25% of these patients will usually have an underlying liver condition such as cirrhosis, biliary atresia, hereditary tyrosinemia, glycogen storage disease, or chronic hepatitis. At diagnosis, half of the patients will have metastatic disease and elevated levels of alpha-feto-protein will be found. In the United States, HCC has a prevalence of 0.2%-0.7% of children, while in Asia and sub-Saharan Africa a prevalence of 5.5% has been reported (Katzenstein et al. 2003).
A total of 65% of patients with HCC will be older than 10 years of age. The typical presentation will be a child with an abdominal mass or abdominal distension on physical examination. Although not common, abdominal pain, anorexia, weight loss, or hemoperitoneum may also be present (Katzenstein et al. 2003).
Macroscopically, a mass that involves both the right and left lobes will be found in 70% of cases. On histological analysis HCC will show giant tumor cells with large trabeculae arranged in an acinar pattern. Necrosis and vascular involvement are commonly seen. Often there is vascular invasion of the portal system and less frequently that of the hepatic vein and IVC. A variant of HCC is fibrola-mellar HCC, which will present with a central scar in 76% of patients on macroscopic examination.
HCC can be represented on US as a hypo- or hyperechogenic mass depending on the amount of fat, or even as a heterogeneous mass with ill-defined borders located in the hepatic parenchyma. It may look identical to a hepatoblastoma. The presence of shadowing foci within the tumor will suggest intratumor calcifications. Evaluation of vascular invasion and dilatation of the portal vein will be seen with color Doppler with conventional gray-scale US (Siegel 2000) (Fig. 4.10a).
On unenhanced CT, HCC is shown as a low attenuation heterogeneous mass. Heterogenicity in attenuation indicates either necrosis or hemorrhage. Lesions may be missed if early vascular imaging is not performed. On enhanced CT, a heterogeneous hypervascularity may be seen. Tumors smaller than 3 cm tend to enhance on arterial phase, while in larger tumors this enhancement pattern is non-specific. Fibrolamellar HCC has specific features on CT. It will be seen as a mass with well-defined borders, calcifications, central scar and abdominal lymph-adenopathy. The tumor will enhance in a heterogeneous pattern and show areas of hypervascularity (Siegel 2000; Ichikawa et al. 1999). The central scar does not enhance in the arterial phase but may do so in the portal or equilibrium phase (Fig. 4.10b,c).
On MRI, HCC will show low signal intensity on T1-weighted images and high signal intensity or isoin-
Fig. 4.10a-c. Hepatocellular carcinoma. a US: irregular echo texture with areas of shadowing. Enhanced CT of the liver arterial phase (b) and portal phase (c) shows the slightly enhanced lesion with a suggestion of a central scar (arrows)
a b c tense to surrounding liver on T2-weighted images. Sometimes hyperintense areas might be seen on T1-weighted images and will represent hemorrhage or steatosis. A central scar may be present and is characteristic of fibrolamellar HCC. Other neoplasias such as focal nodular hyperplasia may also present with a central scar, but in fibrolamellar HCC the central scar will depict lower signal intensity compared with the surrounding tumor, while in focal nodular hyperpla-sia the central scar has high signal intensity on T2-weighted images. Vascular evaluation for thrombus detection involving the portal vein can be carried out with MRI. If the thrombus enhances, this indicates that it is composed of tumor, and will contraindicate embolization or transplantation (Siegel 2000).
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