Morphometric analysis of nucleolar organizer regions in benign and malignant peritoneal effusions using backscattered electron microscopy.

Nucleolar organizer regions are loops of DNA associated with silver-stainable proteins (AgNORs). In general, malignant cells have more and larger AgNORs than benign cells. An inconsistent argyrophilic method and difficulties in objectively evaluating AgNORs account for some of the reluctance to utilize AgNOR staining as a diagnostic tool to differentiate benign and malignant lesions. Sections from paraffin-embedded cell blocks of 10 cases of benign and malignant peritoneal effusions were stained with a modified AgNOR method. Backscattered electron imaging in the scanning electron microscope, together with image analysis, was used to evaluate more objectively a number of AgNOR parameters and to determine which measurement was the most reliable discriminant of the two types of fluids. One hundred nuclei per case were identified and imaged. In contrast to benign nuclei, AgNORs in malignant nuclei were more numerous (P less than 0.0001) and larger (P less than 0.0001). A cut-off mean AgNOR area of 1.1 microns 2 (P less than 0.0001) correctly categorized all malignant (greater than 1.1 microns 2) and benign (less than or equal to 1.1 micron 2) cases. This system's objectivity and specificity could be used to enhance the cytological interpretation of effusions, where the separation of reactive mesothelial cells and malignant cells is extremely difficult.