Diagnostic clues indicating tall cell variants of papillary thyroid carcinoma in fine needle aspiration

BACKGROUND: The definition of tall cell variant of papillary thyroid carcinoma (TCV‐PTC) depends on the articles, and the defined cytological findings characteristic of TCV‐PTC have not yet been fully analyzed. This study aimed to establish the cytological characteristics of TCV‐PTC. METHODS: We retrospectively analyzed the smears of 19 TCV‐PTC and 50 conventional PTC (C‐PTC) cases. RESULTS: Palisaded pattern with the nuclei locating at the base of tall columnar carcinoma cells was seen in 94.7% of TCV‐PTCs, and the incidence was significantly higher than that of C‐PTCs (P < .0001). The palisaded pattern tended to appear at the periphery of the cell clusters. Isolated tall columnar carcinoma cells were present in 89.5% of TCV‐PTCs. The incidence was significantly higher than that of C‐PTC (P = .0001). Tombstone appearance was identified in 78.9% of TCV‐PTCs, but not in C‐PTCs. Spindle‐like carcinoma cells with tapering cytoplasmic end appeared in 68.4% and 12.0% of TCV‐PTC and C‐PTC, respectively (P < .0001). The cytoplasm of TCV‐PTC was densely stained and its cell border was distinct. Cytoplasmic elongation toward an outside of the cell clusters was observed in 89.5% of TCV‐PTCs. CONCLUSION: It is the most important to identify the presence of the tall columnar carcinoma cells on the cytological preparations, in order to distinguish TCV‐PTC from C‐PTC. We propose five cytological findings indicating TCV‐PTC, (1) palisaded pattern, (2) tall columnar cells with the heights of at least three times their widths, (3) tombstone appearance, (4) spindle‐like carcinoma cells, and (5) cytoplasmic elongation.