Parapharyngeal ectopic thyroid: the possible persistence of the lateral thyroid anlage. Clinical case report

The accessory midline thyroids are ascribed to an arrest of migration of the median thyroid anlage, while the lateral ectopic thyroids have induced a hypothesis of the presence of lateral thyroid anlage. We report the case of a 67-year-old man who presented with dyspnea and dysphagia of 1 year's duration. The clinical examination and radiological investigations (CT and MRI) showed a solid heterogeneous mass in the right parapharyngeal space. The fine needle aspiration biopsy was inconsistent. The mass (3x2.5x3.5 cm) was excised via a transoral approach. It was capsulated with an elastic consistency and showed a nodular appearance on the cut surface. Histological examination revealed thyroid tissue with the characteristics of colloid goiter. The postoperative (99m)Tc-pertechnetate scan showed the normal thyroid gland located in the usual pretracheal site. The absence of malignancy, at histology and immunohistochemistry, allows a metastatic nature of the mass to be ruled out, and accounts for a supernumerary thyroid. The occurrence of a parapharyngeal thyroid, although extremely rare, is worth bearing in mind as a possible ectopic location. This case also supports the hypothesized role of the lateral thyroid anlage in man deriving from the ultimo-branchial body in the morphogenesis of the lateral lobe of the thyroid gland.