What are the most appropriate ancillary studies to be used in the workup of a difficult effusion cytology case?)
One of the more difficult problems encountered in diagnostic cytology can be the differential diagnosis between reactive mesothelial cells, adenocarcinoma, and mesothelioma in effusion specimens. This distinction is especially challenging when there are relatively few or cytologically bland-appearing malignant cells present in an inflammatory background or associated with numerous benign mesothelial cells. A variety of ancillary techniques, including routine histochemistry, immunocytochemistry, electron microscopy, and flow cytometry, have been applied in an attempt to solve these problematic effusions. This review will discuss the benefits and limitations of these ancillary techniques in effusion cytology.
Histochemistry
Routine histochemical studies, including staining for mucicarmine and/or alcian blue with and without hyaluronidase treatment, can be helpful in the workup of occasional cases. However, these studies suffer from a lack of sensitivity, as intracytoplasmic mucin may be present in only 40%-60% of adenocarcinomas. Hyaluronidasesensitive alcian blue staining is seen in a similarly low number of mesotheliomas. Moreover, focal intracytoplasmic mucicarmine-positive material can be present in up to 5% of epithelioid mesotheliomas. The main advantage of mucin stains is that they can be performed readily in the pathology laboratory due to their relatively low cost and simplicity.