Distinguishing tall cell variant of papillary thyroid carcinoma from usual variant of papillary thyroid carcinoma in cytologic specimens.

Tall cell variant (TCV) is an aggressive form of papillary thyroid carcinoma (PTC), usually associated with higher local recurrence and distant metastasis. Some authors have suggested that TCV can be effectively diagnosed on thyroid fine-needle aspiration (FNA); this diagnosis may help clinicians plan a more effective treatment regimen. The objective of this study was to compare the FNA specimens of TCV with those of usual variant of PTC (UV-PTC) and to define a set of distinguishing cytologic features. Thirty FNA specimens of histologically proven TCV were compared with 32 FNA specimens of histologically proven UV-PTC. All specimens were evaluated for the following features: papillary groups (PG), elongated/tall cells (EL/TC), oncocytic cytoplasm (OC), distinct cell borders (DCB), prominent central nucleoli (PCN), intranuclear grooves (NG), and intranuclear inclusions (NI). These features were semiquantitatively measured on a sliding scale of 0-4 in both air-dried Diff-Quik-stained and ethanol-fixed Papanicolaou-stained preparations. TCV showed distinctive cytologic features, which can distinguish them from UV-PTC. These included EL/TC, OC, and DCB and were also found to be statistically significant (P < 0.0001). No significant differences were noted for PG and NG. The NIs in TCV cases were qualitatively different than those in UV-PTC. In TCV there were multiple inclusions within the same nucleus imparting a "soap bubble appearance" to the nucleus. This feature was seen in almost all cases of TCV and was rarely seen in usual PTC. On the basis of the above-mentioned cytologic features, TCV can be distinguished from usual PTC in FNA specimens.