Significance of intercellular spaces (windows) in effusion fluid cytology: a study of 46 samples

The presence and nature of intercellular windows were studied on 46 body cavity fluid samples chosen on the basis of an unequivocal diagnosis on May-Grünwald-Giemsa (MGG)/Papanicolaou-stained smears and cell blocks. Of these, 24 cases had adenocarcinoma (AC) and seven had reactive mesothelium (RM) with 15 having distinct populations of both. Mucicarmine and PAS stains were used wherever indicated. The specificity of windows for predicting reactive mesothelium was evaluated. Intercellular windows were found in all cases of reactive mesothelium coinciding with the presence of the fuzzy peripheral microvillous borders. Surprisingly, as many as 17/39 (44%) of the adenocarcinomas also exhibited this feature, of which 13 had a distinctly visible evenly distributed ciliated cell membrane. In addition, 30/39 (77%) cases of AC exhibited a "window-like" appearance caused by cytoplasmic vacuolation. None of the adenocarcinoma clusters with true window formation showed positivity for the mucin stains, whereas all the clusters with pseudowindows caused by vacuolation were stained. Thus the specificity of intercellular windows for RM was merely 56%, though the sensitivity was 100%. On the other hand, the absence of windows was 100% specific for adenocarcinoma. Intercellular windows, though a feature of reactive mesothelial cell populations, can also be found in cases of ciliated adenocarcinomas and may not have a significant predictive value.