ABSTRACT
Interpreting pleural fluid specimens is often a challenging task even for the experienced cytopathologists. Reactive but benign epithelial cells may closely resemble malignancies in effusion cytomorphology; conversely, carcinoma cells in pleural effusions can be deceptively bland. Mesenchymal and hematopoietic proliferations likewise may require extensive additional studies with adjunctive techniques. This chapter aims to describe current approaches for the resolution of interpretative problems in cytopathology of the pleura. Conditions such as hemothorax, chylothorax and pneumothorax relating to structural disorders of the chest are not considered herein, because their diagnosis are relatively straightforward.
