The UK Royal College of Pathologists Thyroid Fine-Needle Aspiration Diagnostic Classification Is a Robust Tool for the Clinical Management of Abnormal Thyroid Nodules

Abstract

Objective: To compare the outcomes and evaluate the relative risk of thyroid cancer by using the UK thyroid fine-needle aspiration (FNA) cytological diagnostic categories, with the main objective being the clarity of patient management. Study Design: Results of thyroid FNA reported as Thy3a, Thy3f, Thy4, and Thy5 were correlated with histological outcomes. The specificity and positive predictive value (PPV; risk of malignancy) for each reporting category was assessed. Results: Of a total of 873 thyroid FNAs, 237 (27%) were reported as ‘abnormal’: 40 (4.6%) as Thy3a, 119 (13.6%) as Thy3f, 20 (2.2%) as Thy4, and 58 (6.6%) as Thy 5. The final outcomes were available in 136 (57%) cases which underwent surgical resection (25, 60, 55, and 74% of Thy3a, Thy3f, Thy4, and Thy5, respectively). The known outcomes of the Thy3a category were too low to be statistically significant. The specificity and PPV of the Thy3f, Thy4, and Thy5 (equivalent to the Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) IV, V, and VI) categories were 50, 50, and 100% and 28, 64, and 100%, respectively. The PPV of Thy3f for diagnosis of ‘neoplasms’ (benign and malignant) was 63%. Conclusion: The current thyroid FNA classification system used in the UK, which is comparable to TBSRTC, offers a sound basis for clear communication on which the management of patients with abnormal thyroid FNA findings can be based. Categories Thy3f, Thy4, and Thy5 carry a progressively rising risk of malignancy, justifying their continuing use. Diagnostic category Thy5 ‘malignant’ is robust and can be used as a sure indication of a definitive surgical management.