Thyroid teratoma in an 11-month-old infant.

We report a case of congenital benign thyroid teratoma in an 11-month-old male infant who was found to have right thyroid gland mass since birth. The tumor was 25 x 20 x 15 mm with whole thin capsule and could be easily dissected from the surrounding normal thyroid tissue at surgery. Histologically, tumor had mature derivatives of the three primordial germ layers with a variety of benign and well-differentiated elements. It was the most conspicuous feature that the tumor was composed mainly of the neurological tissue resembling brain tissue with glial cells and ependymal epithelium components. There were a few anastomosing variably sized tubules and cysts lined by ependymal epithelial cells with papillary feature and retinal pigment epithelial cells. In summary, benign teratoma of thyroid gland in an 11-month-old infant was morphologically and immunophenotypically identified.