Performance of current ultrasound-based malignancy risk stratification systems for thyroid nodules in patients with follicular neoplasms

OBJECTIVES: To investigate the ability of the currently used ultrasound-based malignancy risk stratification systems for thyroid neoplasms (ATA, AACE/ACE/AME, K-TIRADS, EU-TIRADS, ACR-TIRADS and C-TIRADS) in distinguishing follicular thyroid carcinoma (FTC) from follicular thyroid adenoma (FTA). Additionally, we evaluated the ability of these systems in correctly determining the indication for biopsy. METHODS: Three hundred twenty-nine follicular neoplasms with definitive postoperative histopathology were included. The nodules were categorized according to each of six stratification systems, based on ultrasound findings. We dichotomized nodules into the positive predictive group of FTC (high and intermediate risk) and negative group of FTC based on the classification results. Missed biopsy was defined as neoplasms that were diagnosed as FTCs but for which biopsy was not indicated based on lesion classification. Unnecessary biopsy was defined as neoplasms that were diagnosed as FTAs but for whom biopsy was considered indicated based on classification. The diagnostic performance and missed and unnecessary biopsy rates were evaluated for each stratification system. RESULTS: The area under the curve of each system for distinguishing follicular neoplasms was < 0.700 (range, 0.511–0.611). The missed biopsy rates were 9.0–22.4%. The missed biopsy rates for lesions ≤ 4 cm and lesions sized 2–4 cm were 16.2–35.1% and 0–20.0%, respectively. Unnecessary biopsy rates were 65.3–93.1%. In ≤ 4 cm group, the unnecessary biopsy rates were 62.2–89.7%. CONCLUSION: The malignancy risk stratification systems can select appropriate nodules for biopsy in follicular neoplasms, while they have limitations in distinguishing follicular neoplasms and reducing unnecessary biopsy. Specific stratification systems and recommendations should be established for follicular neoplasms. KEY POINTS: • Current ultrasound-based malignancy risk stratification systems of thyroid nodules had low efficiency in the characterization of follicular neoplasms. • The adopted stratification systems showed acceptable performance for selecting FTC for biopsy but unsatisfactory performance for reducing unnecessary biopsy. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00330-021-08450-3.