Thyroid vertebrates. In fish, it is usually located below the gills and is not always divided into distinct lobes. However, in some teleosts, patches of thyroid tissue are found elsewhere in the body, associated with the kidneys, spleen, heart, or eyes. In tetrapods, the thyroid is always found somewhere in the neck region. In most tetrapod species, there are two paired thyroid glands – that is, the right and left lobes are not joined together. However, there is only ever a single thyroid gland in most mammals, and the shape found in humans is common to many other species. In larval
Computed tomography of the thyroid region, or within the parotid gland substance (Fig. 17). The origin of lateral ectopic thyroid tissue is not fully understood. Although this is controversial, some authors suggest that it might have originated from lateral thyroid anlagen (ultimobranchial bodies) that failed to fuse with the median anlage during caudal migration. A thyroglossal duct cyst (TDC) is a duct remnant between the foramen cecum and thyroid isthmus. Most TDCs are located below the hyoid bone and in the midline. The more caudal the cyst, the more likely it will be off midline within 2 cm (Fig. 19 and and20).20). On a CT