Technical and methodological aspects of silver staining and measurement of nucleolar organizer region (NOR)

In the last few years the NOR silver-staining technique has been introduced in tumor pathology for both diagnostic and prognostic purposes, but the lack of a standardized staining protocol has frequently led to misinterpretation of actual structures evaluated by the various authors. Recent data have demonstrated that AgNOR area is closely related to the whole stained nucleolar area obtained by prolonging the silver staining reaction beyond the optimal time for selective NOR visualization. In order to compare data from different laboratories, we propose to stain the whole nucleolus by silver and to measure the dimensions of the silver-stained nucleoli by image analysis.