Interpretation of fine-needle aspirates processed by the ThinPrep technique: cytologic artifacts and diagnostic pitfalls.

The improvement in quality of cytologic preparations with the use of the ThinPrep methodology has been well-documented, but the cytologic artifacts resulting from this technique have not been adequately described. This study describes and illustrates the cytologic artifacts introduced by the ThinPrep technique when used on fine-needle aspirates (FNAs), and evaluates these artifacts as potential diagnostic pitfalls. We reviewed a total of 120 FNAs simultaneously processed by both conventional smears and ThinPrep. FNAs were obtained from the following sites: lymph node (27), breast (23), soft-tissue sites (20), salivary glands (13), gastrointestinal tract (10), lung (9), thyroid gland (13), liver (3), adrenal gland (1), and kidney (1). The ThinPrep smears were consistently devoid of obscuring elements, and the cells were adequately preserved and evenly dispersed. However, we noted some cytomorphologic alterations that should be recognized to avoid erroneous diagnoses. The size of cell clusters was decreased, large branching sheets were fragmented, and there were more single cells, resulting in apparent discohesion. Small cells such as lymphocytes tended to aggregate. All cells were generally smaller and occasionally spindled, the chromatin detail was attenuated, and nucleoli were more prominent. Intranuclear inclusions were difficult to visualize. Background matrix was often altered in both quantity and quality. Extracellular particles, small mononuclear cells, red blood cells, and myoepithelial cells were markedly decreased in number. The pathologist should be cautious in interpreting FNAs prepared using ThinPrep if that is the only methodology employed. Familiarity with artifacts is essential to avoid misinterpretations.