About 2 percent of children develop solitary thyroid nodules. Most of these are benign, including inflammatory lesions or follicular adenomas, but a few are malignant.
The thyroid gland in children is particularly susceptible to irradiation and carcinogenesis. As a result, children with thyroid cancer tend to present with advanced disease. As compared with adults, children with thyroid cancer display a greater frequency of lymph node metastases and distant metastases at the time of diagnosis and higher rates of recurrence during the first decade after diagnosis. Despite these characteristics, children with thyroid cancer generally have a good prognosis.
The evaluation of a child presenting with a thyroid nodule, and an overview of the treatment of thyroid carcinoma is discussed in this topic review. Congenital and acquired goiter and thyroid cysts are discussed separately. (See "Congenital and acquired goiter in children".)
In a study conducted in the southwestern United States, thyroid nodules detectable by palpation were present in 1.8 percent of school children between the ages of 11 and 18 years . In a follow-up study 20 years later, nodules were present in only 0.45 percent of the same subjects, showing that nodules disappeared in 75 percent of subjects . Most thyroid nodules in children are benign. Estimates of the rate of malignancy vary widely but are probably less than one percent.
The following calculations suggest that the proportion of thyroid nodules that are malignant in children is less than 1 percent: In a report from the Surveillance, Epidemiology and End Results (SEER) registry from 1973 through 2004, there were a total of 1753 pediatric patients with thyroid cancer, with an annual incidence of 0.54 cases per 100,000 population . An annual incidence of 0.54 per 100,000 is equivalent to a prevalence of 10 per 100,000 children aged 1 to 18 years. If 1.8 per 100 children have solitary nodules, but only 10 per 100,000 children develop cancer, approximately only 1 in 180 solitary nodules represents thyroid cancer (0.5 percent). Older studies had suggested substantially higher malignancy rates in children with thyroid nodules, ranging from 2 to 40 percent [4,5]. The higher percentages likely represent "referral bias" of children with increased risk factors for thyroid cancer.