Long microvilli of mesothelioma are conspicuous in pleural effusions processed by Ultrafast Papanicolaou stain.
BACKGROUND
The differentiation of malignant epithelial mesothelioma, nonmucinous pulmonary adenocarcinoma, and mesothelial hyperplasia by direct light microscopic examination is challenging. The detection of long microvilli, an ultrastructural feature unique for malignant epithelial mesothelioma, requires immunolabeling of epithelial membrane antigen to be visible by light microscopy. The purpose of this study is to report that this feature is now made conspicuous enough to be detected by light microscopy by a different approach in cytologic processing.


METHODS
The study includes 9 cases of mesothelioma, 50 cases of mesothelial hyperplasia, and 50 cases of nonmucinous pulmonary adenocarcinoma. Direct smears were made from the sediments of fresh or refrigerated effusions, air dried, rehydrated with normal saline for 30 seconds to create retraction halos, and processed with the Ultrafast Papanicolaou stain (UFP).


RESULTS
Long microvilli in thick bundles as well as short, fine projections radiating from the free surface of the epithelial mesothelioma cells were observed within the retraction halos in pleural effusions processed by UFP. These features were not observed in the UFP-processed hyperplastic mesothelial cells or in the pulmonary nonmucinous adenocarcinoma cells.


CONCLUSIONS
Direct visualization of long microvilli via UFP may aid in the distinction of malignant mesothelioma from mesothelial hyperplasia and adenocarcinoma before immunohistochemical and electron microscopic studies are performed.
Yang
Grace C H
GC
Department of Pathology, New York University School of Medicine, New York, New York, USA. grace.yang@nyu.edu
D000230:Adenocarcinoma; D000328:Adult; D000368:Aged; D004396:Coloring Agents; D003937:Diagnosis, Differential; D004847:Epithelial Cells / Q000648:ultrastructure; D004848:Epithelium / Q000473:pathology; D005260:Female; D006416:Hematoxylin; D006801:Humans; D006965:Hyperplasia; D007202:Indicators and Reagents; D008175:Lung Neoplasms / Q000175:diagnosis / Q000473:pathology; D008297:Male; D008654:Mesothelioma / Q000175:diagnosis / Q000473:pathology*; D008871:Microvilli / Q000473:pathology*; D008875:Middle Aged; D010996:Pleural Effusion / Q000473:pathology*
D004396:Coloring Agents; D007202:Indicators and Reagents; D006416:Hematoxylin