The lingual thyroid is the most common form of thyroid ectopy. The ectopic tissue may display any disease affecting the thyroid, including malignancies, which have an estimated incidence of less than 1%. To date only 51 cases of lingual thyroid cancer were reported. Analogously to what observed in orthotopic thyroid, papillary carcinoma is the predominant histotype in lingual thyroid carcinoma. The higher frequency of lingual follicular thyroid carcinoma previously reported is possibly related to histological misclassification in some early reports, prior to the standardization of histological typing of differentiated thyroid carcinomas. Nonetheless, the frequency of the follicular histotype is not negligible, accounting for about one-third of the reported cases. Both natural history and prognosis of lingual thyroid carcinoma are poorly known, likely because of the rarity of the disease and the heterogeneity in the therapeutic approach. However, among the cases more recently reported, surgical excision of the mass, either alone or followed by radioiodine ablation, is the first-line approach, with only two cases treated by radioiodine alone. The nonsignificant rate of neoplastic transformation in lingual thyroid should encourage efforts to obtain a widely accepted consensus for the management of this rare condition, along with standardization of either diagnostic or therapeutic handling of malignancies arising in ectopic thyroid.
Keywords: Ectopic thyroid; Lingual thyroid; Lingual thyroid carcinoma.