Risk of malignancy in thyroid nodules selected for fine needle aspiration biopsy based on ultrasound risk stratification

Aim Risk stratification of thyroid nodules based on ultrasound scan (USS) features using the TIRADS- or U-scale has been widely adopted. However, management decisions for patients whose work-up provide conflicting information, remains challenging. The aim of this study was to assess the rate of malignancy among those with suspicious cytology after USS-evaluation. Methods Retrospective review of clinical, radiological and pathological data regarding patients presenting with a thyroid nodule. Results Between January 2018 and December 2020, a total of 214 patients underwent surgery after presenting with thyroid nodule(s) and a fine-needle aspiration (FNA) cytology report either suspicious (Thy3–4) or diagnostic (Thy5) for thyroid malignancy. The appearance on USS was stratified using the TIRADS-scale, either to select nodules needing FNA-assessment or to characterise palpable nodules. For Thy3a-cytology, the risk of malignancy remained low, irrespective of USS-appearance (2/15 in TIRADS2-3 versus 2/9 in TIRADS 4-5). For a Thy3f-cytology, the risk of malignancy was higher if the USS-appearance was also suspicious (11/75 in TIRADS2-3 versus 17/69 in TIRADS 4-5, p=0.03). High-risk USS-appearance (TIRADS 4-5) in the presence of suspicious/diagnostic cytology (Thy4-5) had a 95% positive predictive value (40/42) of malignancy. Future data collection should assess the risk of malignancy when USS-appearance is malignant (TIRADS 5) yet cytology is benign (Thy2). Conclusion The performance of USS and FNA in this cohort corroborates published data. Until genetic panels will complement the assessment of nodules with a Thy3-cytology, diagnostic thyroid lobectomy remains necessary, as the USS has limited ability to increase the yield of malignant nodules.