Cell blocks are a useful adjunct to smears and monolayer slides in the evaluation of cytologic specimens. Their preparation captures residual small tissue fragments, clots, and cellular sediment, providing additional morphologic information in diagnostically challenging cases. 1,2 In addition, the use of cell blocks enables further immunostaining of paraffin embedded sections. Like other methods of slide preparation, however, this procedure is potentially prone to contamination by organic and inorganic material such as pollen, insects, and fungal organisms. 3 We describe a pseudo-outbreak of budding yeast forms found on cell block slides related to extrinsic contamination of the cell block process.
Index Case
A 29-year-old man developed a Staphylococcal lugdunensis infection following arthroscopic surgery of his knee. He was treated with an arthroscopic ''washout'' and intravenous antibiotics. Despite this, pain and swelling in his knee progressed and he underwent joint aspiration on June 30, 2008, for re-evaluation. The synovial fluid appeared grossly turbid and was sent ''stat'' for cytologic exam. The patient was immediately taken to the operating room for arthrotomy, synovectomy, and debridement. Inflamed and necrotic-appearing tissue from the site was sent for culture and histopathology. Cytology of the synovial fluid was reviewed ahead and showed marked acute inflammation. In addition, budding yeast forms were noted in the cell block which lacked pseudohyphae, measured 2-5 microns in diameter, and were present in both H&E and Gomori methenamine silver (GMS) stained sections obtained from the same cell block (Fig. 1). Intraoperative specimens likewise showed acute inflammation but no organisms were seen and cultures were negative. Because of this unexpected finding, the clinician asked to review the cell block with the pathologist. Gram positive cocci in clusters consistent with Staphylococcus sp. were seen in addition to the yeast (Fig. 2). The ThinPrep TM , processed from the synovial fluid separately, was negative for yeast forms. Furthermore, cell blocks from other patient specimens processed on the same day were noted to have the same fungal organisms. This prompted an epidemiologic investigation to identify the source of cell block contamination.