Management of thyroid cytological material, preanalytical procedures and bio-banking

Thyroid nodules are common and are increasingly detected due to recent advances in imaging techniques. However, clinically relevant thyroid cancer is rare and the mortality from aggressive thyroid cancer remains constant. Fine needle aspiration cytology (FNAC) is a standard method for diagnosing thyroid malignancy and the discrimination of malignant nodules from goitre. As the examined nodules on thyroid FNAC are often small incidental findings, it is important to maintain a low rate of undetermined diagnoses requiring further clinical work up or surgery. The most important factors determining the accuracy of the cytological diagnosis and suitability for biobanking of thyroid FNACs are the quality of the sample and availability of adequate tissue for auxiliary studies. This article discusses technical aspects (preanalytics) of performing thyroid FNAC, including image guidance and rapid on-site evaluation, sample collection methods (conventional slides, liquid-based methods, cell blocks) and storage (bio-banking). The spectrum of special studies (immunocytochemistry on direct slides or liquid-based cytology, immunohistochemistry on cell blocks and molecular methods) required for improving the precision of the cytological diagnosis of the thyroid nodules is also discussed.