Cytological features in the early diagnosis of papillary carcinoma of thyroid in clinically inapparent cases

Background: Papillary thyroid carcinoma (PTC) is the most common among the thyroid malignancies. Fine needle aspiration cytology (FNAC) is the first line investigation in the diagnosis of thyroid lesions. Here we review the significance of certain features conventionally considered to be diagnostic of papillary thyroid carcinoma on FNAC – including type of background, type of colloid, presence or absence of papillary clusters, intranuclear inclusions and nuclear grooves which were also considered for their importance in early diagnosis of PTC. Methods : We reviewed all the thyroid FNACs performed over 18 months period and correlated them clinically and histopathologically, wherever available.  Results : Out of a total of 354 cases of thyroid FNACs, histopathological correlation was possible in 90 cases, with a concordant diagnosis in 82 cases. Analysis of the 8 discordant FNAC smears revealed papillary clusters along with nuclear features, especially nuclear grooves to be the most important finding in indicating a diagnosis of PTC. Conclusion : Although the presence of papillary clusters along with characteristic nuclear features on FNAC is well known to indicate diagnosis of PTC, these findings can be easily missed on cytology smears, especially when the lesions are small (less than 1 cm) and diagnosis is clinically inapparent. Hence, we propose that the presence of papillary clusters in any case should alert the pathologist towards a diagnosis of PTC. A diligent search for nuclear features should follow. Thus a high index of suspicion while examining the FNAC smears in these patients will help in early detection of PTC.