Criteria to Evaluate Tumor Enlargement During the Active Surveillance of High-Risk Thyroid Nodules: Which is Better, Diameter or Volume?

Introduction Tumor enlargement is the most common parameter identifying disease progression during active surveillance, but the value and significance of the changes in tumor diameter and volume in the evaluation of tumor growth have not been compared. Methods This cohort study included 468 patients with high-risk thyroid nodule, in whom nodule size change was monitored using ultrasound, to compare the changes in tumor diameter and volume in assessing tumor growth. Results A total of 569 high-risk thyroid nodules were found in the 468 patients. A total of 14 nodules (2.5%) showed a diameter increase ≥ 3 mm. The number of nodules with a peak volume change exceeding 50% and 100% was 185 (32.5%) and 86 (15.1%), respectively. Among the 555 stable nodules, the number of nodules with volume fluctuations exceeding 50% and 100% was 171 (30.8%) and 72 (13.0%), respectively. Among 212 stable nodules at the baseline and in the first three follow-up, the percentage of peak volume fluctuations exceeding 50% (48.5% vs. 28.5%, p = 0.004) and 100% (26.5% vs. 8.3%, p < 0.001) in the nodules with the sum of three diameters (SOTDs) ≤ 1 cm was significantly higher than that of nodules with SOTDs > 1 cm. A statistically significant difference was also found in the range distribution of SOTDs ≤ 1 cm and SOTDs > 1 cm ( p = 0.007). Conclusions Volume is not an appropriate method for determining tumor growth. Tumor diameter measurement alone serves as a better surrogate for disease progression in sonographically high-risk thyroid nodules than volume.