Thyroid, Parathyroid, and Adrenal Gland Imaging
The thyroid is a bilobed structure evolving from the fourth and fifth branchial pouches. It is initially attached to the ventral floor of the pharynx by the thyroglossal duct. Thyroid tissue may be found anywhere between the base of the tongue and the retrosternal anterior mediastinum (Figure 13.1). The fetal thyroid gland begins to concentrate iodine and synthesize thyroid hormones by approximately 10.5 weeks, which is pertinent when the administration of 131I to fertile women is contemplated. The two ellipsoid lobes of the adult thyroid are joined by a thin isthmus. Each lobe is approximately 2 cm in thickness and width and averages 4–4.5 cm in length. The thyroid gland, averaging approximately 20 grams in weight, resides in the neck at the level of the cricoid cartilage. A pyramidal lobe is present in approximately 30–50%, arising fromeither the isthmus or the superomedial aspect of either lobe; it undergoes progressive atrophy in adulthood but may be prominent in patients with Graves' disease. Although the right lobe tends to be somewhat larger than the left lobe, there is a great deal of variability in both size and shape of the normal gland.
KeywordsThyroid Nodule Thyroid Stimulate Hormone Medullary Thyroid Carcinoma Parathyroid Adenoma Differentiate Thyroid Cancer
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