Hepatocellular carcinoma (HCC) is the most common primary malignancy of the liver and usually develops in patients with cirrhosis. HCC does occur in the non-cirrhotic liver as well. Incidence of HCC is particularly high in patients with cirrhosis from chronic hepatitis C infection, chronic hepatitis B infection, and alcoholic liver disease (Kelekis et al. 1998).
Small hepatocellular carcinoma
Small HCCs (<2 cm) are frequently isointense on T2-weighted images. Isointensity on T2-weighted images may correlate with well-differentiated HCC. Signal intensity on T1-weighted image varies from moderately low to moderately high. High signal intensity on T1- weighted images may reflect the presence of fat or protein (Hussain et al. 2002). The most sensitive sequence for detecting small HCCs is hepatic arterial dominant-phase imaging, in which the majority of small tumors will enhance moderately; not uncommonly these tumors may only be apparent on this set of images (Hussain et al. 2002). Intense enhancement revealed on early phase images is not specific to HCC, as high-grade dysplastic nodules (DNs) may show similar findings. Rarely, small HCCs may be hypovascular, shown by a minimal extent of enhancement on arterial dominantphase images (Hussain et al. 2002).
Isovascular hepatocellular carcinoma
Isovascular HCCs on arterial-phase images have been reported, and attention should be paid to interstitial-phase images that may show washout of the tumors with capsule enhancement (Hussain et al. 2002).
Large hepatocellular carcinoma
Large HCC (>2 cm) may range from hypo- to hyperintense on T2- and T1-weighted images. The most frequent appearance is mildly high signal intensity on T2-weighted images and minimally low signal intensity on T1-weighted images (Hussain et al. 2002). The hyperintensity on T2-weighted images and hypointensity on T1-weigthed images are highly suggestive of moderately differentiated HCC (Hussain et al. 2002). In the interstitial phase, large HCCs tend to demonstrate washout below the signal intensity of background parenchyma, and capsule enhancement, which may only be apparent around some portions of the tumor (Hussain et al. 2002).
The typical signal intensity of a capsule is mildly hyperintense on T2-weighted images, hypointense on T1- weighted images; negligible mild enhancement occurs on immediate post-gadolinium images, which becomes more intense on interstitial-phase images. Tumor extension occurs most commonly into portal veins; however, hepatic venous extension also occurs. Higher doses of gadolinium or higher flow rates may improve visualization of HCCs that may possess minimal increased vascularity (Kelekis et al. 1998; Hussain et al. 2002). Newer contrast agents with higher T1 relaxivity may aid in lesion detection of hypovascular, isovascular, or minimally hypervascular tumors.
Diffuse hepatocellular carcinoma
The most common appearance of diffuse infiltrative HCC is extensive hepatic parenchymal involvement with mottled punctate mildly to moderately high signal intensity on T2-weighted images and mildly to moderately low signal on T1-weighted images. A patchy or miliary pattern of enhancement is often observed on immediate post-gadolinium images with tumor washout and segments of late capsule enhancement on late images.
Diffuse HCC may also appear as irregular linear strands that are iso- to moderately hyperintense on T2- weighted images and hypo- to isointense on T1-weighted images. On immediate post-gadolinium images these tumor strands tend to enhance variably. Late increased enhancement of the tumor strands may reflect a high fibrous composition. Portal vein thrombus is associated with diffuse HCC (Hussain et al. 2002).
Tumor thrombus is commonly of high signal intensity on T2-weighted images and enhances with gadolinium; meanwhile, bland thrombus is low in signal intensity on T2-weighted images and does not enhance after gadolinium (Hussain et al. 2002).