Mucicarminophilic histiocytosis (benign signet-ring cells) and hyperplastic mesothelial cells: two mimics of metastatic carcinoma within a single lymph node.

We describe a unique case of simultaneous signet-ring histiocytes containing polyvinylpyrrolidone (mucicarminophilic histiocytosis) and hyperplastic mesothelial cells within a single supraclavicular lymph node. Both types of cells expanded the nodal sinuses and were initially suspected of being metastatic carcinoma. Histologic features suggested the correct diagnoses, which were confirmed by histochemical and immunohistochemical staining. It is important for pathologists to be aware of these phenomena, so as to avoid a misdiagnosis of metastatic carcinoma.