Natural history and long-term follow-up of incidental thyroid nodules on CT imaging

Incidental thyroid nodules (ITNs) are found in up to 25% of CT scans. Increased use of cross-sectional imaging has contributed to the increased incidence of thyroid cancer worldwide. ITNs pose a management dilemma since nodule malignancy rate is 5%-15% but most cancers are indolent and prognosis in differentiated thyroid cancer is excellent. Study aims are to determine prevalence of ITNs ≥1 cm on CT scans, evaluate reporting practices, assess for emergence of clinically evident thyroid cancer during 13-year follow-up and assess interim nodule growth and clinical outcomes in nodules that were further investigated.

Direct image review of 1499 consecutive CT scans that included the thyroid, performed during January 2009 in a large NHS health board was performed. Clinical data up to January 2022 was analysed in 150 patients with at least 1 ITN ≥1 cm.

ITN prevalence was 11% with mean patient age 70 years and mean nodule diameter 17.5 mm. 30% of ITNs were mentioned in the CT report. During the follow-up period 11% proceeded to thyroid ultrasound, 5% fine needle aspiration, and 2% diagnostic hemithyroidectomy with no thyroid malignancy found. One hundred twenty patients (80%) were deceased by the study endpoint, none from thyroid malignancy. No patients presented with clinically evident thyroid malignancy during follow-up.

None of 150 ITN cases developed clinically evident thyroid malignancy in a 13-year follow-up period with 80% of patients deceased by the study endpoint from non-thyroid causes.

This would suggest that ITNs detected on CT do not require further investigation unless malignant appearances or significant clinical concern for thyroid malignancy.