A case of inflammatory hepatocellular adenoma displaying an unusual histological pattern.

Hepatocellular adenoma (HCA) is a rare type of liver tumor. Here, we report a variant case of HCA in a 56-year-old Japanese man which displayed unusual histological features. The patient had undergone surgery for esophageal and gastric cancer 2 years prior. A computed tomography scan performed in the follow-up period detected a single lesion (diameter 1.4 cm) in the right posterior lobe of the liver, leading to a partial hepatectomy. Histologically, the lesion was composed of two different types of cells. The larger cells, which accounted for most of the cells in the tumor, exhibited granular and eosinophilic cytoplasm, large nuclei and apparent nucleoli. These cells, which were designated the common cells, were typical of the HCA. The other cells, which were designated the pyknotic cells, were smaller, possessed an eosinophilic, homogeneous cytoplasm and pyknotic small nuclei, but did not contain nucleoli. Immunohistochemically, the common cells reacted strongly positive for C-reactive protein and serum amyloid A, which is compatible with a diagnosis of inflammatory HCA; in contrast, the pyknotic cells tested negative for these molecules. Since the pyknotic cells tested positive for several markers of apoptosis, they were considered to be apoptotic. In addition, as the common cells demonstrated a higher ki-67 labeling index, the lesion was considered to display upregulated cell kinetics, i.e. increases in both cell growth and death. Although HCA is a rare type of tumor, there have been several reports on HCA variants. The case reported here is that of a new type of HCA variant that demonstrated an unusual histological pattern and upregulated cell kinetics.