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Distinctive case. Adult mesenchymal hamartoma of the liver: report of a case with light microscopic, FNA cytology, immunohistochemistry, and ultrastructural studies and review of the literature.

We are reporting a case of a mesenchymal hamartoma of the liver (MHL), found incidentally in a 69-yr-old woman. By light microscopy, the tumor was composed of cellular undifferentiated mesenchymal tissue, with pronounced cystic degeneration, and staining strongly positively for vimentin and negatively for cytokeratin. The cysts contained mucoid material and were lined by modified mesenchymal cells, staining positively for vimentin and negatively for epithelial or endothelial markers. Bile ducts scattered within the tumor and on its periphery stained positively for cytokeratin. No alpha-fetoprotein (AFP) or alpha 1-antitrypsin was identified. Fine needle aspiration (FNA) cytology of the tumor revealed loose clusters of oval cells with benign-appearing nuclei within a mucoid background. As observed by electron microscopy, the tumor cells were oval to spindle shaped with interconnected cytoplasmic processes forming intercellular cystic spaces, appearing to be the precursors of the larger cysts seen by light microscopy. MHL was initially considered as a tumor restricted to childhood; however, a few cases in young adults have since been described. With this case, the possibility of MHL occurrence in advanced age is documented.