[Pathomorphologic characteristics and differential diagnosis of small hepatocellular carcinoma].

Recent advances in various diagnostic imagings have made possible early diagnosis of hepatocellular carcinoma (HCC). Grossly, small HCCs of the early stage up to around 1.5 cm in diameter are vaguely demarcated from surrounding liver tissue. Such minute tumors are classified as small HCC with indistinct margins. Histologically, these tumors consist of uniform distribution of well-differentiated cancerous tissues, which are characterized by increased cell density with increased nuclear/cytoplasmic ratio, irregular thin-trabecular pattern with occasional pseudoglandular structure, and frequent fatty and/or clear cell change. In all small HCCs with indistinct margins, varying numbers of portal tracts are contained within the cancerous tissues. None of them represents invasion of the portal vein or intrahepatic metastasis. Thus, small HCC with indistinct margins is considered to be HCC of the earliest stage that can be clinically detected at this moment. Along with the increase of resected small HCCs, hyperplastic lesions such as adenomatous hyperplasia (AH) and atypical AH, which are difficult to differentiate from well-differentiated HCC have also been found. Atypical AH is considered a borderline malignancy. Some focal nodular hyperplasias and liver cell adenomas are also difficult to differentiate from well-differentiated HCC. It should be recalled that some metastatic tumors such as carcinoid tumor, renal cell carcinoma and hepatoid adenocarcinoma also resemble HCC.