Ultrasound features of thyroid follicular adenoma and follicular carcinoma: A narrative review

Follicular thyroid adenoma and follicular thyroid carcinoma are highly similar in terms of cell morphology. As preoperative differentiation relies on histopathology, a large number of patients with benign nodules undergo unnecessary surgery. This narrative review summarizes the value and limitations of ultrasonography in distinguishing between these two conditions. Evidence suggests that follicular thyroid adenoma often presents as well-defined, isoechoic nodules with predominantly peripheral vascularity, while follicular thyroid carcinoma often exhibits a taller-than-wide shape, irregular margins, disordered internal vascularity, and sonographic signs suggestive of capsular interruption or vascular invasion. However, there is considerable overlap between the two in terms of echogenicity, calcification, and vascularity parameters, and the traditional thyroid imaging reporting and data system has limited discriminatory efficacy for follicular tumors (area under the curve: 0.6-0.75). Emerging techniques such as contrast-enhanced ultrasound, elastography, and artificial intelligence have demonstrated improved diagnostic accuracy (reportedly up to 91.2%); however, challenges remain, including limited sample size and poor model interpretability. Future research should focus on multimodal fusion models, ultrasound omics, and molecular marker integration to achieve noninvasive and precise preoperative classification. This review was guided by the Scale for the Assessment of Narrative Review Articles.