Heterotopic mediastinal thyroid.
نویسنده
چکیده
Developmental aberrations of the thyroid gland are common. It develops from pharyngeal endoderm, appearing in the fourth embryonic week as a hollow median outgrowth from the floor of the primitive pharynx at the site of the future foramen caecum of the tongue. The thyroid rudiment lies in intimate relationship with the aortic sac, being in direct contact with its endothelium. The rudiment grows downwards on a hollow stalk, the thyroglossal duct or canal of His, in close relationship with tissues which will later form the body of the hyoid bone. The lingual end of the thyroglossal duct persists as the foramen caecum. Functionally active aberrant thyroid tissue may be found at the base of the tongue, along the normal course of the thyroglossal duct, in the anterior mediastinum, in the pericardium, or in the heart (Willis, 1958). Heterotopic thyroid in the mediastinum, pericardium, and heart has probably grown from rudiments of developing thyroid dragged into the chest during descent of the heart and great vessels with the development of the embryonic neck and the unfolding of the embryo. Heterotopic thyroid tissue in the anterior mediastinum usually lies in the vicinity of the thymus, and may or may not have an obvious connexion with the normally situated cervical thyroid. Mediastinal heterotopic goitre is an entity distinct from retrosternal extension of one or other of the inferior poles of a cervical goitre. Heterotopic thyroid in the mediastinum may derive its blood supply locally or from vessels originating in the neck. It may on rare occasions be the only functioning thyroid tissue. The patient harbouring heterotopic thyroid tissue in the mediastinum is usually symptomless, and presents because of the finding of an anterior mediastinal opacity on a chest radiograph made for unrelated reasons. The diagnosis of heterotopic thyroid is unlikely to be considered. The common lesions in the anterior mediastinum are teratomata and thymic tumours, and it is with either of these diagnoses that thoracotomy is likely to be undertaken. Preliminary investigations are unlikely to have been of value unless they included the exhibition of radioactive iodine and scanning of the mediastinum. The value of this manceuvre has been demonstrated by Swedenburg, Tuttle, and Corrigan (1955), who identified 10 anterior mediastinal lesions as thyroid in this way. Heterotopic mediastinal thyroid is not rare, relative to other anterior mediastinal tumours. Three examples have been found over a decade in the Regional Thoracic Unit in Edinburgh, which subserves a population of about 12 million. During the same period only 21 anterior mediastinal teratomata were found, and slightly fewer tumours of thymic origin, most of which were benign. Details from the three patients found to have heterotopic mediastinal thyroids are presented. In none was the diagnosis suspected before thoracotomy. All are well following resection. Two have been shown to have normal thyroid tissue in the neck, and the third is clinically euthyroid 10 years after resection of the mediastinal tumour.
منابع مشابه
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ورودعنوان ژورنال:
- Thorax
دوره 16 شماره
صفحات -
تاریخ انتشار 1961