Positive cytology findings and a negative histological diagnosis of papillary thyroid carcinoma in the thyroid: is it a false-positive cytology or a disappearing tumor?

BACKGROUND It infrequently occurs that cytologic diagnosis of papillary thyroid carcinoma (PTC) cannot be confirmed by histology after surgery. This phenomenon may be a false-positive cytology or a true disappearing tumor. OBJECTIVES We evaluated patients who had consistent findings of PTC at fine needle aspiration cytology (FNAC) and no evidence of PTC in surgical specimens. METHODS Positive cytology findings and a negative histological diagnosis of PTC in the thyroid was defined as thyroid nodules with FNAC findings of PTC prior to surgery and no evidence of malignancy on histological examination of surgically removed thyroids. We retrospectively reviewed patients who underwent fine needle aspiration (FNA) and thyroidectomy in Asan Medical Center from 2004 to 2012. RESULTS Six patients were found who fit the definition of positive cytology findings and a negative histological diagnosis of PTC in the thyroid. The FNAC diagnosis of 6 patients was 'malignancy
 ' suggesting PTC according to the Bethesda system. All patients underwent thyroidectomy with central neck dissection. Three patients had reactive changes after FNA due to needle passage. Among these 3 patients, 2 had pathologically confirmed metastatic PTC in dissected lymph nodes. These 2 patients could be defined as true disappearing PTC in the thyroid after FNA. The remaining 3 patients had neither histologic alterations nor evidence of PTC in the thyroid and lymph nodes specimens. CONCLUSIONS Both disappearing PTC and a false-positive result of FNAC should be considered in patients with positive cytology findings and a negative histological diagnosis of PTC in the thyroid.