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.