Hepatocellular Carcinoma

Abstract

Hepatocellular carcinoma (HCC) is the fifth most common tumor in the world and is the third most common cause of cancer-related death, after lung cancer and stomach cancer. The strongest predisposing factor for developing HCC is liver cirrhosis, and approximately 80 % of cases of HCC have been developed in a cirrhotic liver. Liver cirrhosis is characterized by irreversible remodeling of the hepatic architecture with bridging fibrosis and formation of a spectrum of hepatocellular nodules, including regenerative nodules (RNs), dysplastic nodules (DNs), and HCCs. These cirrhosis-associated hepatocellular nodules result from the localized proliferation of hepatocytes and their supporting stroma in response to liver injury. The development of HCC in a cirrhotic liver is described as a multistep progression, from low-grade DN to high-grade DN, then to DN with microscopic foci of HCC, then to small well-differentiated HCC, and finally to overt carcinoma. There is increasing evidence to support a multistep model of the process of human hepatocarcinogenesis. Precursor lesions are characterized by the appearance of dysplastic lesions in the form of microscopic dysplastic foci and macroscopic dysplastic nodules. However, also a de novo development of HCC can occur, and it has been usually seen on normal liver parenchyma without evidence of cirrhosis or nodules in European and American people who have the low incidence of chronic liver disease. The differentiation of these cirrhosis-associated hepatocellular nodules and early detection of HCC is important, because the most effective treatment for HCC is surgical resection or transplantation, and local ablation therapy when the HCC is small. However, detection of small and early stage HCCs and characterization of cirrhosis-related nodules remains the most challenging area in liver imaging. Currently, various imaging modalities such as ultrasound (US), computed tomography (CT), magnetic resonance (MR) imaging, and positron-emission tomography (PET) have been used for the detection and diagnosis of HCC. Among these, dynamic contrast-enhanced CT and MR are considered as a first-line modality for the diagnosis and therapeutic planning in HCC, as they are able to provide reliable information regarding tumor vascularity which is related to sinusoid capillarization and neoangiogenesis of the HCC during the hepatocarcinogenesis. Furthermore, recent advances in MR imaging such as diffusion-weighted imaging (DWI) and newly developed dedicated MR contrast agents that target hepatocyte have facilitated the detection and characterization of small HCCs, and optimal management of cirrhotic patients. Early diagnosis and definitive treatment remains the key to long-term outcome. A multidisciplinary approach is critical to the successful management of hepatocellular carcinoma. Currently, imaging plays a crucial role in detection, characterization, therapeutic planning, and posttreatment follow-up for HCC.