Abstract

The diagnosis of well-differentiated thyroid cancers, which constitute the majority of pediatric thyroid malignancies, relies on neck ultrasonography (US) and fine-needle aspiration biopsy (FNAB). Thyroid scintigraphy has a limited role at this stage. Based on US and FNAB findings—with molecular tests, if possible—the surgical approach is determined. In some cases, additional cross-sectional imaging may be required for preoperative evaluation. Postoperatively, the patient is referred to Nuclear Medicine for consideration of radioactive iodine (RAI) therapy. The presence of residual thyroid tissue is assessed using thyroid scintigraphy (Tc-99m pertechnetate, I-123 or I-131). Radioiodine imaging also allows for whole-body scanning. Cervical lymph nodes are evaluated with neck US. If surgically resectable residual cervical metastatic disease is detected, reoperation should be considered before RAI therapy. Serum thyroid-stimulating hormone (TSH), thyroglobulin (Tg), and anti-Tg antibody levels should be measured. Elevated Tg levels raise suspicion for distant metastases, particularly in the lungs, and warrant evaluation with non-contrast chest computed tomography. Pathology findings—including tumor subtype, invasive features, and the location and number of metastatic lymph nodes—are integrated to determine the patient’s risk category. RAI therapy is not recommended for low risk patients. When indicated, I-131 activity is generally administered empirically, with adult doses adjusted for the pediatric population. All patients should undergo follow-up with TSH suppression. Recurrence most commonly occurs in cervical lymph nodes, while persistent distant metastases are most often observed in the lungs. Management may include reoperation, additional RAI therapy or TSH suppression on a case-by-case basis. Although RAI refractory disease is rare in children, systemic therapies—either for therapeutic or redifferentiation purposes—should be considered when there is clinically significant progression that cannot be controlled with local treatments.