Thyroid Anatomy
The thyroid is a highly vascular, brownish-red gland located anteriorly in the lower neck, extending from the level of the fifth cervical vertebra down to the first thoracic. It’s formed by 2 elongated lateral lobes with superior and inferior poles connected by a median isthmus which is overlying the second to fourth tracheal rings.
The thyroid weight varies, however; it averages 25-30 g in adults (it is slightly heavier in women).
A conical pyramidal lobe often ascends from the isthmus or the adjacent part of either lobe (more often the left) toward the hyoid bone, to which it may be attached by a fibrous or fibromuscular band
The thyroid is supplied with arterial blood from the superior thyroid artery, a branch of the external carotid artery, and the inferior thyroid artery, a branch of the thyrocervical trunk, and sometimes by an anatomical variant the thyroid ima artery, branching directly from the subclavian artery.
The thyroid nerve supply if from the external branch of superior laryngeal and the recurrent laryngeal nerves.
The Recurrent Laryngeal Nerve (RLN) is a branch of the vagus nerve (cranial nerve X) that supplies all the intrinsic muscles of the larynx (voice box), with the exception of the cricothyroid muscles. There are two recurrent laryngeal nerves, right and left, in the human body. The right and left nerves are not symmetrical, with the left nerve looping under the aortic arch, and the right nerve looping under the right subclavian artery then traveling upwards. They both travel alongside of the trachea. Additionally, the nerves are one of few nerves that follow a recurrent course, moving in the opposite direction to the nerve they branch from, a fact from which they gain their name.
