Thyroid fine-needle aspiration and The Bethesda Classification System

Fine-needle aspiration (FNA) is a cornerstone in diagnosing thyroid nodules. For decades, Danish FNA has been categorised into the groups: "FNA not performed", "Inadequate", "Cystic", "Inconclusive", "Benign", "Suspicious", "Malignant" and "Information missing". Internationally, The Bethesda Classification System (TBCS) is increasingly accepted, especially owing to a detailed specification of FNA suspicious for malignancy. The Danish "Suspicious" group is very broad and includes atypia, follicular neoplasia and FNA suspicious of other malignancies. The purpose of this study was to apply TBCS to the Danish "Suspicious" FNA group and to estimate the frequency of malignancy in the individual Bethesda groups (BG).

This descriptive study is based on a prospective cohort from the THYKIR database. It includes 479 patients with a "Suspicious" FNA and surgical treatment in The Region of Southern Denmark from 2001 to 2013. Based on pathology records, FNA was classified according to the TBCS. Malignancy was determined by the histological diagnosis from the THYKIR database.

The Danish "Suspicious" group was allocated to the BG I, II, III, IV, V and VI with a malignancy risk of 36.4%, 13.3%, 17.2%, 16.1%, 55.3% and 88.2%, respectively.

The Danish "Suspicious" group contains a broad spectrum of BG with varying malignancy risk. The results indicate a need for standardisation of the Danish FNA classification. A national introduction of the TBCS might secure an international and comparable standard.

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