"Histiocytoid" cells in fine-needle aspirations of papillary carcinoma of the thyroid: frequency and significance of an under-recognized cytologic pattern.

BACKGROUND

Although the classic cytologic features of papillary carcinoma of the thyroid in fine-needle aspirates have been well described, one uncommon feature, a vacuolated, histocyte-like cell without classic nuclear changes of papillary carcinoma, has been less well characterized.

METHODS

The author reviewed a large series of thyroid aspirates for specimens with these cytologic features.

RESULTS

Seven specimens were identified, representing approximately 6% of all aspirates with the features of papillary carcinoma and less than 0.5% of all aspirates. The cells resembled histiocytes but were larger, more atypical, and keratin positive in the one specimen that was tested. The cells had enlarged nuclei with abundant cytoplasm that often was vacuolated. The nuclei had grainy chromatin, occasional nucleoli, and lacked grooves and prominent pseudoinclusions. The background showed numerous, hemosiderin-laden macrophages typical of cyst contents in only three specimens. Calcifications were present in six specimens and resembled psammoma bodies in two specimens. Three specimens showed papillary carcinoma at resection, two specimens had other passes from the same nodule that were diagnostic of papillary carcinoma, and two specimens were from recent patients without follow-up. Only one of the three resected tumors showed prominent cystic change. None of 50 aspirates that were diagnosed as benign cyst contents had similar atypical cells, nor did resections of six predominantly cystic, benign lesions.

CONCLUSIONS

Histiocytoid cells are present in as many as 6% of all aspirates in which some features of papillary carcinoma are present. Increased awareness of these cells may help improve the sensitivity of fine-needle aspiration for the diagnosis of papillary carcinoma of the thyroid.