Objective: To investigate the important cytologic features and thyroglobulin (Tg) level in fine needle aspiration cytology (FNAC) of cystic metastasis of papillary thyroid carcinoma (PTC) and to find some independent cytologic factors that enhance the diagnostic accuracy of cystic lymph node metastasis without identifiable tumor cells or high levels of Tg.
Study design: Two hundred forty-four aspiration cytology cases with correspondent tissue specimens were included in the study. Cytologic features and FNAC Tg level were evaluated in each case.
Results: Twelve cases showed cystic lymph node metastasis in tissue slides but negative cytology with a mean FNAC Tg level of 413.3 ng/mL (range, 71.9-963.0). Out of these, 10 cases (83.3%) demonstrated only foamy macrophages.
Conclusion: Foamy macrophages only without Tg level information in FNAC could raise the possibility of cystic metastatic PTC even if no identifiable tumor cells are found.