Objective:

To compare progression outcomes during active surveillance between highly suspicious thyroid nodules located in the isthmus and those in non-isthmic regions, and to explore the feasibility of active surveillance for selected isthmic lesions.

Key Findings:

• Median follow-up duration was 47 months with no significant difference in progression rates between isthmic and non-isthmic nodules.
• Non-isthmic nodules had larger volumes at baseline and final follow-up.
• 30.30% of isthmus group and 24.52% of non-isthmus group showed a ≥50% increase in volume.
• Composite endpoint occurred in 3.03% of isthmus group and 4.09% of non-isthmus group.
• No distant metastases or thyroid cancer-related deaths occurred during follow-up.

Interpretation:

ACR TI-RADS 5 thyroid nodules in the isthmus do not exhibit higher progression rates than non-isthmic nodules during active surveillance, suggesting potential feasibility for monitoring selected isthmic nodules.

Limitations:

• Small sample size of isthmic nodules.
• Low number of progression events limits definitive conclusions.

Conclusion:

The findings support the potential feasibility of active surveillance for selected isthmic nodules under careful monitoring.