Thyroid and Parathyroid Gland Anatomy

• The lecture is about the thyroid and parathyroid gland
• It has clinical significance in the head and neck

Thyroid Gland

• Shaped like an H
• Weighs approximately 25 grams
• Its lateral lobes have a pyramidal shape.
• Key features include apex, base, three surfaces, and two borders.
• Measures about 5x3x2cm
• It's a highly vascular ductless gland.
• Located at the C5, C6, C7, and T1 vertebrae levels.
• Serves as its own hormone storehouse
• Dependent on external environment for raw materials
• Has the richest blood supply of any gland.
• The true capsule is a peripheral condensation of connective tissues and the false capsule is derived from the pretracheal layer, thin on the posterior aspect
• The suspensory ligament of Berry is formed by the thickening of the false capsule connecting the lateral lobe and connects it to the cricoid cartilage of the larynx

Presenting Parts and Relations

• Two lateral lobes are pyramidal in shape
• They have an apex, base, two borders, and three surfaces.
• The apex is sandwiched between inferior constrictor and sternothyroid
• Related to the STA & ELN
• The base of the gland extends up to the 5th or 6th tracheal ring
• Related to the ITA & RLN
• The anterior border relates to the superior thyroid artery
• The posterior border relates to four parathyroid glands

Apex and Base

• Apex is directed upward towards the thyroid cartilage
• The superior thyroid artery and external laryngeal nerve diverge close to the gland's apex
• Any ligation during procedures should be close to gland to avoid nerve damage
• The base extends up to the 5th or 6th tracheal ring
• The inferior thyroid artery and recurrent laryngeal nerve are in close relation towards the base.
• Any ligations should be away from it to avoid nerve injury

Medial Surface

• Includes the sternohyoid and superior belly of omohyoid
• The Postero-lateral surface relates to carotid sheath contents
• It has two tubes (trachea and esophagus)
• Two muscles: inferior constrictor and cricothyroid
• Two nerves include the external and recurrent laryngeal nerves

Isthmus

• Connects two lobes.
• A pyramidal lobe occasionally extends upwards from the isthmus close to the midline.
• Anteriorly related to sternothyroid and sternohyoid muscles.
• Posteriorly related to Second, third, and fourth tracheal rings.

Blood and Nerve Supply

• Arterial supply from the superior and inferior thyroid artery
• Venous drainage from the superior, middle, and inferior thyroid veins
• Lymphatic drainage flows through the pre-laryngeal, pre-tracheal, and jugulo-digastric group of lymph nodes
• Innervation consists of parasympathetic (vagus and recurrent laryngeal nerves) and sympathetic (superior, middle, and inferior cervical ganglia) components

Clinical Implications

• Enlargement, called goiter, occurs due to hyper or hypothyroidism

Parathyroid Gland

• Essential Endocrine glands
• Tiny, lentiform, yellowish-brown bodies, measuring 6x3x2cm
• Weigh about 50mg
• Located on the posterior border of the thyroid gland
• Number varies but generally found in two pairs

Parathyroid Glands

• Consists of 2 Pairs on the posterior border of the thyroid gland
• The superior pair, parathyroid IV, is more consistent in position at the level of the inferior border of the cricoid cartilage
• The inferior pair, parathyroid III, is more variable in position but usually lies close to the inferior pole
• 1-5% of people have an inferior parathyroid that may be in the superior mediastinum

Vessels and Nerves

• Arterial supply from the Inferior thyroid artery
• Veins & lymphatics are similar to those for the thyroid and thymus
• Nerves from superior & middle cervical sympathetic ganglia