Fine needle aspiration cytology of thyroid nodules: conventional smears vs thin layer technique

Objective: Liquid-based cytology using the thin layer technique has recently been introduced in thyroid fine needle aspiration cytology together with or insubstitution of direct smears, but its usefulness is still controversial and relatively few studies have been published in this field. The aim of the present study was to compare the results obtained from conventional smears with those from thin layer smears. Design: In 3875 thyroid nodules, a double cytologic sampling was taken in randomized order, to prepare conventional or thin layer smears. Main outcome: The diagnoses agreed in 2934 (75.7%) cases and disagreed in 941 (24.3%). The analysis of discordant data showed there were fewer non-diagnostic cases in the thin layer smears (377 vs 541, p < 0.001) whereas in conventional smears there were more cases positive for carcinoma (27 vs 4, p < 0.001). The cytohistologic correlation was available for 194 cases and showed that conventional smears had a greater capacity for revealing carcinomas (44 vs 31). Finally, diagnoses based on conventional smears were more sensitive than thin layer smears (93.6% vs 65.9%) whereas specificity was constant. Conclusions: From our experience, the conventional smear offers a greater possibility of diagnosis when suspecting malignancy or diagnosing malignancy cases, whereas thin layer smears significantly reduce the number of non-diagnostic cases. For this reason, we suggest combining the two techniques in routine cytologic diagnosis.