Nucleolar organizer regions in smears of pleural effusion

Agyrophil staining was applied to nucleolar organizer regions (NOR) to differentiate cells of adenocarcinoma and histiomesotheliosis in pleural effusion. The smears were either nuclearly unstained, but cytoplasmically counterstained by Papanicolaou method or Papanicolaou-destained before agyrophil staining of nucleolar organizer regions (AgNOR). The purposes of this study were to assess the feasibility and usefulness of AgNOR staining in diagnostic cytology and to try to set up a procedure that could be used on prestained smears for retrospective study. All smears showed good background and cellular outline. The distribution of NOR was either intranuclearly or in the nucleoplasm diffusely. In previously nuclearly unstained smears, NOR showed granular to powder-like appearance. The mean number of NOR in adenocarcinoma (38.4 +/- 12.5) was significantly higher than that in histiomesotheliosis (15.6 +/- 2.9). In Papanicolaou-destained smears, the NOR showed confluent dots. The mean number of NOR was much lower as compared to that of previously nuclearly unstained smears. Furthermore, the mean number of NOR in adenocarcinoma (3.6 +/- 1.4) showed no significant difference with that of histiomesotheliosis (2.7 +/- 0.8). In conclusion, AgNOR staining is one of the methods to differentiate benign from malignant cells, but not in Papanicolaou-destained smears.