Cytologic diagnosis of malignant mesothelioma, with particular emphasis on the epithelial noncohesive cell type.

The effusion cytologies from 21 cases of malignant mesothelioma (MM) (15 pleural, 6 peritoneal) diagnosed at the Indiana University Medical Center during 1990-1997 were reviewed. Using the classification of Tao (Acta Cytol 1979;23:209-213), 13 cases of MM were of the epithelial cohesive cell type and 8 were of the epithelial noncohesive cell type. While the epithelial cohesive cell type has been discussed in the literature, the epithelial noncohesive cell type has not. The cytomorphologic features for both types are presented with particular emphasis on the noncohesive cell type. The differential diagnosis and use of ancillary confirmatory laboratory tests are briefly discussed. Because of its resemblance to florid reactive mesothelial hyperplasia and the general lack of awareness of the existence of the single-cell pattern of mesothelioma, this diagnosis can often be missed.