Diagnostic efficacy of conventional as compared to liquid-based cytology in thyroid lesions. Evaluation of 10,360 fine needle aspiration cytology cases

OBJECTIVE: To evaluate the efficacy of thyroid fine needle aspiration cytology (FNAC) processed by liquid-based cytology (LBC) as compared to conventional smears (CS) in 10,360 consecutive cases in 3 reference periods. STUDY DESIGN: In 1997-1998, 2,394 FNACs had CS; in 2001-2002, 3,463 had both CS and LBC; and in 2004-2005, 4,503 had only LBC. Three arbitrary parameters of efficacy were chosen to compare the two different methods: rate of inadequacy (IR), rate of indeterminacy (INDR) and rate of malignancy (MR). In the same biennia 6,184 thyroidectomy specimens were examined. RESULTS: IR was, respectively, 8.4% in 1997-1998, 18.4% in 2001-2002 and 13.3% in 2004-2005. MR was respectively 2.2%, 2.5% and 2.2%. INDR was 16.6% in 1997-1998, 23.3% in 2001-2002 and 15.9% in 2004-2005. In each biennium, respectively, 16.9%, 27.6% and 28% of malignant neoplasms were histologically diagnosed. CONCLUSION: LBC was used as an alternative method in the cytologic diagnosis for the preoperative selection of thyroid neoplasms, decreasing indeterminate diagnoses without MR changes.