In their article, Knoepp and colleagues promote the utility of fine-needle aspiration (FNA) direct smears for ancillary studies. Indeed, direct smear aspirate slides are a great source of cells available for molecular and fluorescence in situ hybridization studies, in addition to providing archival material. This is important, because cell block material may not always be sufficient to perform ancillary studies, particularly when there is only a single high-quality pass, followed by passes with blood dilution.
In our experience, aspirated material on direct smears can also be superior to cell blocks for documenting infection. In several cases, our FNA smear preparations stained with routine stains (Diff Quik and Papanicolaou stain) as well as special stains to identify microorganisms (Gram, acid fast, and Gomori methenamine silver stains) yielded greater numbers of micro-organisms and superior morphology compared with corresponding cell blocks. For example, more acid fast bacilli could be visualized by negative staining in Diff Quik-stained smears than were present in scant cell block material. Moreover, it was often easier to appreciate septations and branching of fungal hyphae in smears, as opposed to the truncated hyphae present in cell block sections. Therefore, for cases in which infection is suspected, we recommend not only submitting aspirated material for culture, but also preparing additional unstained direct smears from a high-quality pass that can be dedicated for special stains to detect microorganisms.
Russell Silowash, DO
Sara E. Monaco, MD
Liron Pantanowitz, MD
Department of Pathology, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania