Intrathyroidal parathyroid adenoma: Diagnostic pitfalls on fine-needle aspiration: Two case reports and literature review.

Parathyroid adenomas may occur within the thyroid, clinically simulating thyroid nodules. Fine-needle aspiration (FNA) of these presumably "thyroid nodules" can lead to misinterpretation of cytomorphological findings because of similarities in cytological features of parathyroid and thyroid lesions. Here, we reported two cases of intrathyroidal parathyroid adenomas. One of them was misinterpreted as thyroid lesions. The other was composed exclusively of oncocytic cells and had a correct cytological diagnosis. In this study, both cases showed a new cytological feature which has not been reported in the literature: many capillaries protruding outside the three-dimensional fragments without epithelial cells around. Diagn. Cytopathol. 2016;44:921-925.