| Benign | Comments |
| Multinodular (sporadic) goiter ("colloid adenoma") | Colloid adenomas are the most common type of thyroid nodule in certain pediatric populations |
| Hashimoto (chronic lymphocytic) thyroiditis | Autoimmune, often multinodular by ultrasonography |
| Cysts (colloid, simple, or hemorrhagic) | Pure "simple" cysts are always benign; a cyst may be combined with a solid component in colloid nodules |
| Follicular adenomas | |
| Macrofollicular adenomas | |
| Microfollicular or cellular adenomas | |
| Hürthle cell (oxyphil cell) adenomas | Rare in childhood Hürthle cell changes can be seen in degenerating follicular adenomas or with Hashimoto thyroiditis |
| Malignant | Comments |
| Differentiated thyroid cancer | |
| Papillary carcinoma (includes NIFTP) | >85% of pediatric thyroid cancers[1] Bilateral disease is common; primarily lymphatic spread Recurrence rate <1% for NIFTP in adults |
Follicular carcinoma:
| 8 to 9% of pediatric thyroid cancers[1] Typically unifocal; primarily hematogenous spread |
| Hürthle cell (oxyphil cell) carcinoma | Uncommon in childhood |
| Medullary carcinoma | 4% of pediatric thyroid cancers[1]; most are associated with MEN2 |
| Anaplastic carcinoma | Very rare in childhood |
| Primary thyroid lymphoma | Rare in childhood |
| Metastatic carcinoma (renal cell, others) | Rare in childhood |
