1629 The Risk of Malignancy in Cytologically Indeterminate Thyroid Nodules

Fine needle aspiration (FNA) is the gold standard for the diagnostic assessment of thyroid nodules, with cytology stratified using the Thy classification (Thy 1-5). The management of cases where cytology is indeterminate (Thy-3) is challenging and subject to controversy. The current British Thyroid Association guidelines subclassify Thy-3 lesions into Thy-3a (atypia) and Thy-3f (follicular). Repeat FNA is generally recommended for Thy-3a specimens, whilst Thy-3f lesions should proceed to diagnostic hemithyroidectomy. The aim of this study was to determine the risk of malignancy in Thy-3a and Thy-3f lesions. Method This was a retrospective study of all patients who underwent FNA of a thyroid nodule from 01/01/2018 – 31/12/19. Those with Thy-3 cytology were identified and results correlated with final surgical histology. Results In total, there were 179 patients with Thy-3 cytology: 37 Thy-3a and 142 Thy-3f. The rate of malignancy was 21.6% (n = 8) for Thy-3a lesions and 20.4% (n = 29) for Thy-3f. When excluding microcarcinoma, the rates fell to 20.4% (n = 7) and 12.7% (n = 18) respectively. There was no statistically significant difference in malignant conversion between the two groups (p = 0.20). Conclusions This study does not demonstrate any statistically significant difference in the risk of malignancy between the Thy-3a and Thy-3f groups, suggesting that this subclassification does not add any additional utility to clinical decision making. Consideration should be given to the use of local malignant conversion rates to guide further management and pre-operative patient counselling in the Thy3 group.