Ectopic Thyroid is a rare abnormality during fetal embryology resulting to aberrations or abnormal migration of thyroid tissue outside its usual anatomical position in the pre-tracheal area. True malignant transformation is extremely rare in ectopic thyroid gland. Evidence shows that the likelihood of malignancy in ectopic thyroid is extremely low with <1% of cases. Among these rare cases, Papillary Thyroid Carcinoma was the most common. Studies have shown that in 70% of ectopic thyroid cases, the normal thyroid gland is not present. This is a rare case of ectopic thyroid cancer in the superior mediastinum with a normally located thyroid gland that exhibits benign nodules. A 56-year-old man, with no known co-morbidities, who works as an ambulance driver, underwent an annual medical examination. On chest radiograph, an incidental finding of a soft tissue opacity was seen at the superior mediastinum, associated with rightward deviation of the tracheal column. The patient has no subjective complaints. No hoarseness, no dysphagia, and no difficulty breathing. The patient was then advised to seek a consultation at the Outpatient Department. On examination, a palpable, solid, firm anterior neck mass was noted, measuring 2 cm, that moves with deglutition. No palpable cervical lymphadenopathy was appreciated. Further work-up noted bilateral thyroid nodules, TIRADS 4, Bethesda V.

The patient underwent flexible laryngoscopy with bronchoscopy, total thyroidectomy, full sternotomy, and excision of the superior mediastinal mass. Final histopathology revealed Papillary Thyroid Carcinoma in the superior mediastinal mass and Follicular Nodular Disease in the thyroid gland. Intraoperatively, there was no communication and point of attachment appreciated between the cervical thyroid gland and the apex of the mass just inferior to the gland.

On histopathology, the superior mediastinal mass was found to be a Papillary Thyroid Carcinoma, encapsulated, with a Follicular variant. The thyroid gland showed Follicular Nodular Disease with two unremarkable lymph nodes. The patient was then started on TSH suppressive therapy with administration of Levothyroxine.

Ectopic thyroid is a rare condition that occurs in 1:100,000 – 300,000 individuals. Malignant transformation of ectopic thyroid tissue and its occurrence to the superior mediastinum makes it even rarer. Although a rare entity, ectopic thyroid tissue in the mediastinum is a condition that demands careful consideration despite its limited number of reported cases. Effective preoperative imaging helps alleviate diagnostic dilemmas and provides a reliable diagnosis. It is important to differentiate a goiter with intrathoracic extension from a superior mediastinal neoplasm.