Ectopic Sequestered Thyroid Tissue: An Unusual Cause of a Mediastinal Mass

Abstract

An 80-year-old female presented with an incidental finding of a retrosternal mass on magnetic resonance imaging. Ultrasound demonstrated a mediastinal lesion adjacent to but separate from the inferior pole of the right thyroid lobe. Fine needle aspiration cytology demonstrated colloid and follicular cells. At surgery, the right thyroid lobe was found to be normal. A discrete 5 cm nodule was found in the anterior mediastinum separate from the thyroid and just anterior and to the right of the trachea and thymus. The nodule had a vascular pedicle arising from the mediastinum. The differential diagnosis included metastatic thyroid carcinoma. Histology was consistent with a benign ectopic sequestered thyroid nodule. Extensive investigations demonstrated no sign of a thyroid malignancy.

Missed retrosternal ectopic thyroid tissue in a patient operated for multinodular goiter

“…No malignancy was observed in histopathological examination of the ectopic thyroid tissue. Differential diagnosis of substernal goiter should be considered for thymomas, lymphomas, pleuropericardial cysts, neurogenic tumors, dermoid cysts, and metastatic lymph node deposits of well-differentiated thyroid carcinoma (1,11).…”

“…Ectopic thyroid tissue is commonly seen in the midline of the neck throughout the descending pathway of the thyroid gland (1). Ectopic thyroid tissue can be found from the tongue to the diaphragm.…”

“…Ectopic thyroid tissue is usually seen in the tongue, submandibular region, cervical lymph nodes, larynx, trachea, oesophagus, mediastinum, diaphragm and heart respectively (2,3). Although the most common type of ectopic thyroid tissue is lingual, the most common non-cervical location is the thoracic cavity (1). "Forgotten goiter" is an extremely rare situation which is described as a mediastinal thyroid mass found after total thyroidectomy (4).…”

Ectopic thyroid tissue presenting as a cardiac mass

“…Coronary angiography will identify the blood supply to the tumour and help with surgical planning (1). Overall, the available literature reports generally good results from surgical resection (7,10,13). Once the mass is identified as thyroid tissue, the thyroid must be investigated for evidence of primary malignancy.…”

“…The thyroid descends along the path of the thyroglossal duct in front of the trachea, anterior to the hyoid bone and thyroid cartilage, to its final pre-tracheal position in gestational week 7 (1,5,10). Interruption of this descent is the most common cause for thyroid ectopia (13).…”