Utility of Ultrasound Surveillance for Thyroid Cancer in Children

Background: Differentiated thyroid cancer (DTC) is the most common pediatric endocrine malignancy. The utility of ultrasound (US) surveillance after initial treatment has not been clearly delineated. We sought to evaluate the clinical utility of US for the detection of residual or recurrent disease in pediatric patients with thyroid cancer beginning 1 year after initial therapy. Methods: This is a retrospective cohort study of pediatric patients (<19 years) diagnosed with DTC between 1998 and 2022 whose response to therapy (RTT) one year after initial treatment (thyroidectomy ± radioactive iodine) was excellent or indeterminate. We evaluated the association between sonographic and biochemical findings (thyroglobulin [Tg] and Tg antibodies [TgAb]) at one year with the subsequent diagnosis of residual/recurrent structural disease in the neck (SDN). Results: In total, 112 patients had 1-year RTT that was excellent (n = 61, 54.5%) or indeterminate (n = 51, 45.5%). Median length of subsequent follow-up was 6.4 (interquartile range 3.8-8.9) years. Overall, 683 surveillance neck US were performed, with a mean ± standard deviation of 1.0 ± 0.4 US per patient per year. Of 61 patients with excellent RTT, none developed SDN during follow-up. Eighteen patients (29.5%) had a false-positive indeterminate or abnormal US finding. Of 51 patients with indeterminate RTT, 9 (17.6%) developed SDN during follow-up. SDN was detected by US in 7/9 cases (77.8%). SDN was detected by I-123 scan, but not by US, in two cases (22.2%), both with abnormal Tg/TgAb. 7/9 (77.8%) cases of SDN were detectable by Tg/TgAb. Overall, fine-needle aspiration (FNA) was performed in 17/112 (15.2%) patients and diagnosed SDN in six patients. Overall, 11/112 patients (9.8%) underwent FNA but were not diagnosed with SDN. Conclusions: In pediatric DTC patients with excellent response to initial therapy, the utility of serial US surveillance is limited by the low risk of SDN and frequent false-positive US findings. In children with indeterminate RTT, SDN occurs in a significant proportion and may be detected by US or by abnormal Tg/TgAb levels. These patients may benefit from the combination of US and biochemical surveillance.