Purpose: The aim of this study is to evaluate the specificity of diagnosing PTC by fine needle aspiration (FNA) cytology.
Methods: This study retrospectively reviewed the cytopathological reports of 1066 patients that underwent thyroidectomy based on a diagnosis of PTC by FNA between January 1993 and December 2008. This study re-evaluated the cytology and histopathology of the patients that received false positive diagnoses of PTC by FNA.
Results: Ten patients (0.9 %) received false positive diagnoses of PTC by FNA. Three patients were overdiagnosed as having PTC by FNA cytology. In contrast, the nuclear features of PTC in the other seven cases were confirmed by the retrospective reviews of the patients' FNA cytology. Three of the seven patients showed follicular structures in their resection specimens, thus resulting in a diagnosis of either adenomatous goiter or follicular adenoma. However, PTC could not be diagnosed by histopathology in the remaining four patients, even though the histopathology showed the nuclear features of PTC.
Conclusions: Most cases of PTC can be easily diagnosed by cytological and morphological atypia with certain limitations. The difficulty in diagnosing PTC by cytology is because the pathological features of PTC also occur in some benign thyroid tumors. Therefore, immunohistochemical or molecular biological approaches must be combined with current cytological diagnostic techniques for the diagnosis of PTC.