Tumor Size Discrepancies with Different Measurement Methods in Papillary Thyroid M​​​​​icrocarcinoma

Purpose Measurement of tumor size is critical for thyroid tumor management; however, optimal measurement methods and evaluation criteria remain unclear. This study aimed to quantitatively compare the papillary thyroid microcarcinoma tumor size measured by ultrasound, gross examination, and histological assessment and to determine how discrepancies between these different measurements may influence clinical decision making, such as indications for fine-needle aspiration, eligibility for active surveillance, and surgical management. Materials and methods This study included 412 papillary thyroid carcinoma cases with tumors of < 15 mm on preoperative ultrasound examination. Results The reduction rates of gross and histological sizes compared to ultrasound sizes were 93.5% and 86.9%, respectively. Significant differences were observed between all combinations of ultrasound, gross, and histological sizes ( p< 0.001). Papillary thyroid microcarcinoma accounted for 42.0%, 55.6%, and 65.1% of cases, respectively. In 23 cases, the difference between the ultrasound and gross or histological sizes was >5 mm. This was because they were not cut at the maximal plane, were located in the isthmus or inferior pole, were associated with chronic thyroiditis, and were lobulated. Conclusions We demonstrated that the size of papillary thyroid carcinoma depends on the measurement method used. Gross and histological tumor sizes tended to be smaller than ultrasonographic sizes. Clinicians should be aware that tumors slightly exceeding 10 mm on ultrasound may ultimately be classified as papillary thyroid microcarcinoma postoperatively. Tumor location, shape, and coexisting thyroiditis can all contribute to measurement errors in ultrasound.