Background: Fine needle aspiration cytology is the most accurate tool for diagnosing thyroid nodules. Its accuracy is related to the rate of inadequate samples, which can be minimized with the adoption of on-site assessment of the adequacy of the material. The introduction of liquid-based cytology (LBC) in the thyroid does not allow checking on the adequacy of the cellularity. The possibility of making a second LBC slide for decreasing the number of non-diagnostic cases is studied.
Methods: Out of 553 cases diagnosed in a single institution from January to March 2005, 166 consecutive cases with an LBC slide reviewed by the same pathologist were evaluated. The cases were classified in a five-tiered category system (Thy1 to 5 according to the British Thyroid Association guidelines) and all but two (with cystic degeneration) were processed by LBC and stained with Papanicolaou stain. The above-mentioned categories are defined as follows: Thy1 inadequate or haemorrhagic, Thy2 non-neoplastic lesion; Thy3 follicular lesion/suspected follicular neoplasm; Thy4 suspicious for malignancy; Thy5 diagnostic of malignancy. For each case the cytological diagnosis was made on the LBC slide and the adequacy of the cellularity for a conclusive diagnosis was assessed.
Results: Of the 166 cases, 39 were non-diagnostic (Thy1-inadequate), ten presented features of cystic degeneration (Thy1-haemorrhagic), 90 were benign (Thy2), 22 were diagnosed as a follicular lesion (Thy3), one as suspicious of malignancy (Thy4) and four as papillary carcinoma (Thy5). Thirty-nine cases had a second LBC for achieving a definitive diagnosis with eventual re-classification. Of these cases, 23 (61.5%) led to a conclusive diagnosis (18 Thy2, five Thy3) with a 18.5% decrease of the inadequacy rate.
Conclusions: The making of an additional LBC slide helps in achieving a diagnosis in cases classified as non-diagnostic on the first standard slide (52.1% recovery rate). This procedure is particularly helpful for meeting the adequacy criteria in benign and indeterminate lesions and could also be used for refining the diagnosis of suspicious for a malignant thyroid neoplasm.