Incidence and significance of true papillae in thyroid fine needle aspiration.

INTRODUCTION: Whether true papillae without nuclear features of papillary carcinoma in thyroid fine needle aspirates should be diagnosed as atypia of undetermined significance (AUS) is unclear.

METHODS: The results of all thyroid FNAs performed from 2014-2016 with corresponding resections as well as aspirates from 2000-2016 with a diagnosis of follicular variant of papillary carcinoma or Noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) were reviewed.

RESULTS: Papillae with fibrovascular cores were identified in 17 of 149 consecutive cases (11%), 3 of which had nuclear features of papillary carcinoma and were papillary carcinoma at resection. All 14 cases of papillae without nuclear features of papillary carcinoma were benign. Of 29 papillary carcinomas, papillae were identified in 8 (28%) and "swirls" were identified in 3 (10%) additional cases, all in cases of papillary carcinoma, NOS. Papillae and swirls were not identified in any cases of NIFTP (13 cases) or follicular variants of papillary carcinoma (15 cases).

CONCLUSION: True papillae are relatively common. Both papillae with nuclear atypia and swirls are highly specific for papillary carcinoma, NOS and are not seen in NIFTP. True papillae with fibrovascular cores but without cytologic features of papillary carcinoma are benign and should not be diagnosed as AUS. Diagn. Cytopathol. 2017;45:689-692. © 2017 Wiley Periodicals, Inc.