Converting fluid-based cytologic specimens to histologic specimens for immunohistochemistry

Cavitary effusions are often evaluated cytologically to determine if there is an underlying neoplastic cause. Differentiation of neoplastic epithelial from mesothelial populations within effusions can be difficult using routine cytology. In addition, cytology alone cannot provide information on the immunophenotype of round cell populations. Gel foam techniques can be used to convert effusions into cell blocks for immunohistochemical (IHC) staining which can then be used to differentiate mesothelial from epithelial cell populations, and also allow immunophenotyping of round cell populations within effusions.

The aim of this study was to evaluate a gel foam cell block technique for converting potential neoplastic cells in cavitary effusions into cell blocks to characterize these further by IHC.

Thirteen canine and 7 feline samples with cohesive cell populations were evaluated using gel foam cell blocks and IHC. Samples evaluated by routine cytology were categorized as (1) epithelial cells, (2) cohesive cell population without cytologic distinction between mesothelial and epithelial cells, and (3) mesothelial cells with signs of atypia. Antibody-mediated staining of vimentin and cytokeratin of the effusion cell blocks yielded further classification of cohesive cell populations. In addition, a total of 4 effusions with malignant round cells were evaluated; they were immunophenotyped as either B- or T-cell lymphoma.

The use of cytokeratin and vimentin IHC on gel foam cell blocks from cavitary effusions provided robust staining and allowed characterization of cohesive cells as mesothelial or epithelial and immunophenotyping of lymphoid cell populations. In addition, this method is cost and time effective.