ABSTRACT
ANATOMY During development, the thyroid gland originates as an outpouching of the floor of the pharynx. It grows downward, anterior to the trachea, with the course of its downward migration marked by the thyroglossal duct. The thyroid sits like a saddle over the trachea with the two lateral lobes of the thyroid connected by a thin isthmus, which sits just below the cricoid cartilage. Normally, each lobe is pear shaped, 2.5-4 cm in length, 1.5-2 cm in width, and 1-1.5 cm in thickness; the gland typically weighs 10-20 g in an adult depending upon body size and iodine supply. A pyramidal lobe may extend upward from the isthmus on the surface of the thyroid cartilage and is a remnant of the thyroglossal duct.
