Anatomy of Thyroid and Parathyroid Glands

The thyroid gland is placed on the front of the lower neck, close to the lateral aspects of the larynx and trachea. The isthmus bridging the lobes crosses the second and third rings of the trachea. The gland is covered anteriorly by strap muscles, an investing layer of deep fascia and subcutaneous tissue. The superficial fascia of the neck is a layer of loose connective tissue extending to the face, which is embedded in the voluntary muscles of facial expression and the platysma. The subcutaneous nerves, venules, lymphatics, and portions of the anterior and external jugular veins also pass through this layer. The anterior jugular veins course close to the midline and may assume significant size when the thyroid gland extends to the superior mediastinum, impeding venous drainage. The anterior jugular veins have rare cross-connections in suprasternal space (Space of Burns), which need effective control when the midline is divided. External jugular veins cross obliquely but seldom cause trouble in routine exploration for thyroidectomy (Fig. 4.1). Three pairs of strap muscles (sternothyroid, sternohyoid, and omohyoid) anchor the thyroid gland in the anterior aspect. The sternothyroid muscles are closely applied to each lobe of the thyroid. They are attached to the oblique line of the thyroid cartilage and prevent migration of the enlarged thyroid gland to the anterior aspect of the larynx. But nodules from the superior pole extend the cephaloid towards the submandibular region from behind the sternohyoid muscle close to the carotid sheath on the postero-lateral aspect (Fig. 4.2). Sternocleidomastoid muscles protect the thyroid in the lateral aspect.