Anatomy of the thyroid gland

The thyroid gland lies at the C5-T1 vertebral level, anterior to the trachea, and is a ductless endocrine gland that weighs about 20 grams. The thyroid gland has two lateral lobes connected by an isthmus that lies anterior to the second to fourth tracheal cartilaginous rings. It is enveloped in the visceral layer of the pretracheal fascia. In about 50% of cases, a pyramidal lobe may extend superiorly from the isthmus, demarcating the embryonic migratory pathway of the thyroid from the base of the tongue