Anatomy, Head and Neck, Thyroid

The thyroid gland is a midline structure located in the anterior neck. The thyroid functions as an endocrine gland and is responsible for producing thyroid hormone and calcitonin, thus contributing to the regulation of metabolism, growth, and serum concentrations of electrolytes such as calcium.[1][2] Many disease processes can involve the thyroid gland, and alterations in the production of hormones can result in hypothyroidism or hyperthyroidism. The thyroid gland is involved in inflammatory processes (e.g., thyroiditis), autoimmune processes (e.g., Graves disease), and cancers (e.g., papillary thyroid carcinoma, medullary thyroid carcinoma, and follicular carcinoma). In addition to considering its role in metabolism, growth, regulation of certain electrolytes, and its involvement in many disease processes, the thyroid gland deserves consideration for its anatomical location and its close relationship to important structures including the parathyroid glands, recurrent laryngeal nerves, and certain vasculature. Anatomy Overview The thyroid gland is divided into two lobes that are connected by the isthmus, which crosses the midline of the upper trachea at the second and third tracheal rings. In its anatomic position, the thyroid gland lies posterior to the sternothyroid and sternohyoid muscles, wrapping around the cricoid cartilage and tracheal rings. It is located inferior to the laryngeal thyroid cartilage, typically corresponding to the vertebral levels C5-T1. The thyroid attaches to the trachea via a consolidation of connective tissue, referred to as the lateral suspensory ligament or Berry's ligament. This ligament connects each of the thyroid lobes to the trachea. The thyroid gland, along with the esophagus, pharynx, and trachea, is found within the visceral compartment of the neck which is bound by pretracheal fascia. The "normal" thyroid gland has lateral lobes that are symmetrical with a well-marked centrally located isthmus. The thyroid gland typically contains a pyramidal extension on the posterior-most aspect of each lobe, referred to as the tubercle of Zuckerkandl. Despite these general characteristics, the thyroid gland is known to have many morphologic variations. The position of the thyroid gland and its close relationship with various structures brings about several surgical considerations with clinical relevance.