[Secondary changes in the thyroid gland induced by aspiration cytology]

Due to the introduction of fine needle aspiration cytology (FNAC) to the routine clinical preoperative examination surgical pathologists are faced with thyroid gland specimens with FNAC-induced secondary changes. These changes can cause diagnostic difficulties and be a source of incorrect diagnosis. Authors present a review of FNAC-induced changes with differential diagnostic criteria helpful in these pitfalls. FNAC-induced changes can be schematically divided into two major groups--recent ones (intranodal bleeding and/or necrosis) and subacute/late ones (proliferation of granulation tissue with predominance of myofibroblasts or endothelial cells, resorptive pseudoxantomathous granulomas, formation of sarcoid-like granulomas, capsular pseudoinvasion and scarring). Pathologists should be informed about the previously performed FNAC and must be aware of these lesions to prevent their misinterpretation.