Tall cell variant of papillary thyroid carcinoma: cytologic features and differential diagnostic considerations.

The cytologic features of the tall cell variant (TCV) of papillary thyroid carcinoma may be confused with those of other thyroid neoplasms with different prognoses and treatment modalities. Elucidation of the cytomorphology of this variant would be useful in planning treatment for this fairly aggressive variant of papillary carcinoma. The cytologic features of 20 cases of TCV were compared with those of 23 cases of the usual variant (UV) of papillary thyroid carcinoma and of 10 Hürthle-cell neoplasms (HCN). After a set of features was defined, the efficacy of employing it to distinguish TCV from UV and HCN was assessed by three cytopathologists (J.D.T., I.R., and M.O.), was independently examined 15 unknown cases selected by the first author. Aspirates of TCV showed some specific cytologic features which included large cell size with abundant granular cytoplasm and variably sized nuclei with granular chromatin. The cells were sometimes columnar, but more often were polygonal, and prominent cytoplasmic borders were present in 50% of cases. Intra-nuclear inclusions were more prominent in TCV than in UV. There was some overlap in the cytomorphology of some TCV and UV cases, and variable numbers of cells with UV features were encountered in TCV cases. Employing the cytologic features of TCV listed above, three cytopathologists examined the unknown cases, which included 7 cases of TCV, 4 cases of UV, and 4 cases of HCN. TCV was recognized as such by all three cytopathologists in 6 of 7 cases, and all UV and HCN were correctly typed by all three examiners. The cytologic features of TCV are sufficiently distinctive to enable separation from HCN and most cases of UV. Although the diagnosis of TCV may be rendered employing fine-needle aspiration biopsy, material, this diagnosis should be limited, in our opinion, to specimens which contain at least 30% of cells with typical TCV features.