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Many endocrine diseases are appropriately managed surgically. The details of clinical presentation, diagnosis, and medical management are discussed in other sections of this book. This chapter provides an overview of the principles involved in the surgical therapy for these conditions. The indications for surgical intervention, the relevant procedures, and their risks and benefits are discussed.
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EMBRYOLOGY AND ANATOMY
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The thyroid gland arises in the midline as an endoderm-derived pharyngeal diverticulum around the third week of gestation. The paired median thyroid anlages then descend from their origin at the base of the tongue (foramen cecum) and ultimately form a bilobed thyroid gland anterolateral to the trachea and larynx. The thyroid lobes are connected just below the cricoid cartilage by an isthmus. The connection to the foramen cecum—the thyroglossal duct—separates and is partially resorbed by the sixth week of gestation. Its distal remnant forms the pyramidal lobe. The calcitonin-producing C cells are neuroectodermal in origin, arise from the fourth branchial pouch, and are located in the lateral superoposterior aspect of the gland.
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A number of embryologic or developmental abnormalities of the thyroid have been described and are related to the absence or mutations of thyroid differentiation factors, including thyroid transcription factors 1 and 2 (TTF-1 and TTF-2) and transcription factor Pax 8. Thyroglossal duct cysts are usually found in the midline, just inferior to the hyoid bone. A lingual thyroid results from maldescent of the median thyroid anlage and is often accompanied by agenesis of other thyroid tissue. Rests of thyroid tissue may be found anywhere in the central compartment of the neck, including the anterior mediastinum. Tongues of thyroid tissue are often seen to extend off the lower thyroid poles, particularly in large goiters. In contrast to the above, thyroid tissue in the lateral neck lymph nodes (lateral aberrant thyroid) almost always represents metastatic thyroid cancer and is not a developmental abnormality.
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The adult thyroid gland is reddish-brown in color and weighs approximately 20 g. The thyroid gland is supplied by paired superior and inferior thyroid arteries. The former arise from the external carotid artery and the latter from the thyrocervical trunk. A thyroid ima artery arises directly from the aorta or innominate artery in approximately 2% of individuals and enters the isthmus, replacing an absent inferior artery.
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The thyroid is drained by ...