Limitations of fine‐needle aspiration and core needle biopsies in the diagnosis of tall cell variant of papillary thyroid carcinoma

The tall cell variant papillary thyroid carcinoma (TCV-PTC) shows aggressive behaviour. Thus far, the diagnosis of TCV-PTC can only be confirmed using the postoperative specimen. This study aims to evaluate whether fine-needle aspiration (FNA) or core needle biopsy (CNB) could diagnose TCV-PTC preoperatively.This is a retrospective cohort study. We included adult patients diagnosed with TCV-PTC or PTC with tall cell features (TCF) at final surgical pathology between January 2015 and December 2018. Preoperative histology was reviewed for six cytomorphologic features suggesting TCV-PTC in FNA or the percentage of tall cells in the CNB specimen. The postoperative pathology was also reviewed to confirm the percentage of tall cells.A total of 119 patients were included in this study; 35 (29%) patients with PTC with TCF served as controls. The most frequent cytomorphological feature in FNA samples of TCV-PTC was tall columnar cells, including single tombstone-like cells (70%). Among 43 TCV-PTC evaluated by FNA, 3 FNA (7%) revealed the absence of any of the six cytomorphologic features suggesting TCV-PTC. When we defined 30% of tall cells in CNB specimens as a cutoff suggesting TCV-PTC, only 16 (41%) TCV-PTCs could be preoperatively detected, and 3 (7%) TCV-PTCs did not have any tall cells. The proportion of tall cells was not associated with the postoperative percentage of tall cells.Both cytomorphologic features in FNA and the percentage of tall cells in CNB present limitations for use as accurate preoperative diagnostic tools of TCV-PTC.