A low-power, "architectural," clue to the follicular variant of papillary thyroid adenocarcinoma in aspiration biopsy

OBJECTIVE: To search for low-power, or "architectural," clues to the diagnosis of the follicular variant of papillary thyroid adenocarcinoma (FVP) in Diff-Quik-stained aspiration biopsy smears in order to aid in the rapid diagnosis of FVP, especially as a complement to frozen sections. STUDY DESIGN: The smears of 23 cases, each with tissue-proven FVP, were compared to those of 23 cases of classic papillary thyroid adenocarcinoma (PTA), 23 cases of tissue-proven follicular neoplasms (FN) (i.e., adenoma or well-differentiated adenocarcinoma) and 23 samples of colloid nodules (CN). The low-power (10x) features of the four groups were studied and compared. RESULTS: Our study showed that FVP exhibited monolayered cellular sheets with branched, irregular contours, which can be distinguished from the uniform microfollicles with smooth contours formed in FN and the large, round or oval monolayered sheets of follicular cells found in CN. FVP shared all of the features of classic PTA except for the larger, complex sheets of epithelial cells and psammoma bodies found in the latter. CONCLUSION: The branched sheets of epithelial cells evident during low-power examination of Diff-Quick-stained smears of thyroid aspirates are a ready first clue to the rapid diagnosis of FVP. The diagnosis can be confirmed by subsequent careful evaluation of nuclei in Papanicolaou-stained smears and sections of tissue.