Cyto‐morphological features of parathyroid lesions: Fine‐needle aspiration cytology series from an endocrine tumor referral center

Background Descriptions of parathyroid cell cyto‐morphology are limited. Fine‐needle aspiration cytology (FNAC) with immunocytochemistry (ICC) or biochemical PTH measurements may help verify the parathyroid origin in extraordinary cases, although these methods are nowadays largely replaced by imaging techniques. Methods We collected all available FNAC reports of parathyroid lesions from our department spanning 20 years, to characterize the clinical use of parathyroid FNAC, and to assess morphological correlates between cytology and subsequent histopathology. Results Twenty‐eight cases with assessable cytological smears were found, of which 21 cases were surgically resected and 20 available for histological review (15 adenomas, 2 carcinomas, 2 atypical tumors and a single case with secondary hyperplasia). FNAC was predominantly performed to localize the diseased gland in cases with inconclusive imaging, in cases with a suspicion of intrathyroidal localization or in cases with persistent hypercalcemia following unsuccessful surgery. The diagnosis was verified using either PTH ICC and/or PTH measurements for most cases, and the procedure affected the clinical decision‐making for the majority of patients in this selected cohort. Cytological differences between parathyroid adenomas and carcinomas were found, as only carcinomas showed pleomorphism with irregular nuclei and prominent nucleoli. Morphologically, no correlations to predominant cell types or growth patterns visualized at histological investigations among adenomas were noted, and biopsy artifacts were evident in 40% of cases. Conclusions Parathyroid FNAC could be considered as a complementary analysis for a small group of selected patients, but benefits have to be weighed against the risk of biopsy artifacts in histological preparations.