The thyroid tissue starts developing during the fourth embryonic week. It appears on the tongue as an epithelial growth. By the seventh embryonic week, the thyroid gland descends to the adult position, anterior to the trachea. Ectopic thyroid gland can be found along this pathway, like the region of the neck, the mediastinum, the pharynx, the larynx, the esophagus, the trachea, and around the aorta. On the other hand, intra-abdominal thyroid tissues have been reported scattered within the gallbladder [1
], the mesentery of the small intestine [2
], the pancreas [5
], the porta hepatitis [6
], the duodenum [7
], and the space posterior to the spleen and stomach [8
Some explanations have been suggested for ectopic thyroid. First, metaplasia in nature or that it represents either choristomatous tissue or a teratoma [7
] cannot be excluded. Our case cannot be explained in terms of a metaplastic transformation because the thyroid develops from the endoderm, whereas the adrenal gland develops from the ectoderm and mesoderm. No evidence of teratomatous elements was found. Secondly, all papers reported that ectopic thyroid tissues were limited to the upper abdomen. This suggests that the present case is possibly caused by over-descending hypoglossal duct remnants as well as other manifestations of ectopic thyroid beneath the diaphragm.
Three cases have been reported of ectopic thyroid tissue found in the adrenal gland [3
]. Tsujimura et al
. described the first case, in which a 61-year-old-woman incidentally presented with a cystic lesion in the right adrenal gland. The patient was diagnosed as having ectopic thyroid tissues because the resected tumor was composed of large follicles and follicular epithelium in the cyst wall that stained positively for thyroglobulin. The clinical and pathological features of the two other cases were mostly identical to those of the first reported case and the present case. Because of the recent development of routine health checks, it is now expected that the finding of an adrenal mass with a cystic lesion will occur in an incidental manner. Some diseases, like cortical adenoma, adenocarcinoma, pheochromocytoma, and dermoid cyst are reported to form adrenal cysts [9
]. Ectopic thyroid is one possibility of a differential diagnosis when it shows both a cystic lesion and normal hormonal data.