Incidental solitary hepatocellular carcinomas smaller than 1 cm in size found at autopsy: a morphologic study

The morphologic features and growth pattern of single hepatocellular carcinomas less than or equal to 1 cm in size, found incidentally at autopsy, were studied in nine cases. In all but one case, the hepatic parenchyma showed advanced cirrhosis. In three cases, the hepatocellular carcinomas were localized within a regenerative nodule as a form of "nodule within nodule." The carcinoma was rimmed by nonneoplastic hepatic tissue. A fourth carcinoma consisted of an expansile hepatocellular carcinoma nodule enclosed by a fibrous band of cirrhotic stroma. The remaining five cases consisted of hepatocellular carcinomas which infiltrated the surrounding regenerative nodules or hepatic lobules. These observations suggested that hepatocellular carcinomas arise within regenerative nodules, some of which still retain residual nonneoplastic tissue around the tumor. Others invaded the adjacent liver tissue. The grossly visible fibrous capsule, often seen in more advanced hepatocellular carcinomas, was absent in all cases. All of the hepatocellular carcinomas were well-differentiated. Four cases showed a trabecular pattern with slight sinusoidal dilatation, 3 showed a scirrhous pattern and 2 showed a compact pattern. Their histologic features included marked bile production, Mallory body formation by clusters of tumor cells, resistance to hemosiderin deposition in a markedly siderotic background and loss or decrease of reticulin fibers. These features were hallmarks of small hepatocellular carcinomas. Pathologists should study cirrhotic livers carefully so as not to miss small carcinomas. Clinicians should be aware that even small liver nodules may be hepatocellular carcinomas.