The annual incidence of thyroid cancers is low in children younger than 15 years (2.0 per million people), accounting for approximately 1.5% of all cancers in this age group. Thyroid cancer incidence is higher in children aged 15 to 19 years (17.6 per million people), and it accounts for approximately 8% of cancers arising in this older age group. Most thyroid carcinomas occur in girls.
Patients with thyroid cancer usually present with a thyroid mass with or without cervical adenopathy.[44,45,46,47] When compared to pubertal adolescents, prepubertal children had a more aggressive presentation with a greater degree of extrathyroid extension, lymph node involvement, and lung metastases. However, outcome was similar in the prepubertal and adolescent groups.
There is an excessive frequency of thyroid adenoma and carcinoma in patients who previously received radiation to the neck.[49,50] In the decade following the Chernobyl nuclear incident, there was a tenfold increase in the incidence of thyroid cancer compared to the previous and following decades. When occurring in patients with the multiple endocrine neoplasia syndromes, thyroid cancer may be associated with the development of other types of malignant tumors. (Refer to the Multiple Endocrine Neoplasia (MEN) Syndromes and Carney Complex section of this summary for more information.)
The American Thyroid Association Taskforce  has developed guidelines for management of thyroid nodules in older adolescents and adults, but it is not yet known how to apply these guidelines to thyroid nodules in children.
Initial evaluation of a child or adolescent with a thyroid nodule should include an ultrasound of the thyroid. Tests of thyroid function are usually normal, but thyroglobulin can be elevated. Fine needle aspiration as an initial diagnostic approach is sensitive and useful. However, in doubtful cases, open biopsy or resection should be considered.[53,54,55,56] Open biopsy or resection may be preferable for young children as well.
Various histologies account for the general diagnostic category of carcinoma of the thyroid, but the vast majority of tumors are differentiated. These tumors comprise papillary carcinoma (60%-75%), follicular carcinoma (10%-20%), medullary carcinoma (5%-10%), and anaplastic carcinoma (<1%). Papillary carcinoma often has multicentric origins and a very high rate of lymph node metastasis (70%-90%). Follicular carcinoma may be sporadic or familial and medullary carcinoma is usually familial. Follicular carcinoma is usually encapsulated and has a higher incidence of bone and lung metastasis. Follicular carcinoma and papillary carcinoma (often referred to as differentiated thyroid cancer) generally have a benign course, with a 10-year survival rate of more than 95%. Fifty percent of medullary thyroid carcinomas in adults and children have hematogenous metastases at diagnosis. Patients with medullary carcinoma of the thyroid have a guarded prognosis, unless they have very small tumors (microcarcinoma, defined as <1.0 cm in diameter), which carry a good prognosis. (Refer to the Multiple Endocrine Neoplasia (MEN) Syndromes and Carney Complex section of this summary for more information.)