Occurrence of intercellular spaces (windows) in metastatic adenocarcinoma in serous fluids: a cytomorphologic, histochemical, and ultrastructural study.

The application of cytomorphologic criteria to the examination of serous effusions allows the reliable diagnosis of malignancy in the majority of cases. One feature observed in tissue fragments previously thought to be indicative of mesothelial origin is the presence of intercellular windows, presumably due to long surface microvilli. In this study, however, we examined cytologic preparations of 143 effusion and body-cavity washing specimens and noted distinct intercellular window formation within tissue fragments of adenocarcinoma in 13% of the cases studied. Stains for mucicarmine, Alcian blue with hyaluronidase pretreatment, and periodic acid-Schiff following diastase digestion on corresponding cell block material demonstrated that intercellular mucin contributes to such window formation in greater than half of these cases. Thus the presence of intercellular windows within tissue fragments does not, in isolation, preclude the diagnosis of malignancy in serous effusions.