Thyroid Gland
• It is an endocrine gland which is shaped like a Greek shield.
• The gland has 2 conical lobes each joined by an isthmus in its lower part.
• An inconstant pyramidal lobe may project upwards form the isthmus (Left of the midline) Remnant of
the distal part of the thyroglossal duct
Extent & Location
• In the lower part of the front & side of the neck.
• Gland lies against C5-T1 vertebrae / each lobe extends from the oblique
line of the thyroid cartilage to the 4/5th tracheal rings.
• Isthmus overlies 2nd to 4th tracheal rings. (Palpable)
• Lobes not palpable (because of the tension of the strap muscles)
Capsules & ligaments
• Has 2 capsules.
• True capsule
Derived from peripheral condensation of the connective tissue.
A dense venous plexus lies deep to the this capsule.
• False capsule
Derived from pretracheal Fascia.
Thick along the posterior border where it forms suspensory ligament of Berry where it connects the
lobes to the cricoid cartilage. The recurrent laryngeal nerve is closely related to this ligament.
, Clinical correlations
• During thyroidectomy, removal of the thyroid gland, the gland is removed with the true
capsule to avoid haemorrhages.
Prostate gland also have a true capsule and a false capsule. But in prostate gland, the venous
plexus lies in between the 2 capsules. Therefore, in prostatectomy both capsules are left behind.
Arterial supply
• 2nd most vascular organ
1. Superior thyroid artery.
• The 1st anterior branch of external carotid artery
• Close relation to external laryngeal nerve away from gland.
• At the upper pole divides into anterior and posterior branches.
• Divides into branches after piercing false capsule
• External laryngeal nerve deviates at the apex of a lobe of the gland. Therefore, during thyroidectomy
superior thyroid artery is ligated near the gland
• Anterior branch anastomoses with the same branch of opposite side.
2. Inferior thyroid artery.
• Branch of thyrocervical trunk
• Passes behind the carotid sheath and middle cervical sympathetic ganglion & in front of the vertebral
vessels.
• Close relation to recurrent laryngeal nerve near the gland. Individual branches are ligated to maintain
the blood supply to parathyroid gland.
• Divides into branches before piercing false capsule.
• Ascending branch anastomoses with posterior branch of superior thyroid artery.
3.Additional supply
• Thyroidea ima artery (brachiocephalic or arch of aorta) (about 3% of population)
• Oesophageal and tracheal branches (accessory thyroid arteries).
• Clinical correlations,
During thyroidectomy, the superior thyroid artery is ligated near the gland to save external laryngeal
nerve while the inferior thyroid artery is ligated distal to the gland to save recurrent laryngeal nerve.
• Superior thyroid artery reaches the upper pole of the gland and anastomosis with the opposite artery
along the upper border of the isthmus.
• Inferior thyroid artery reaches the lower pole.
Deep Neck Page 6
Anatomy ©2020 A/L Batch Repeat Campaign
• It is an endocrine gland which is shaped like a Greek shield.
• The gland has 2 conical lobes each joined by an isthmus in its lower part.
• An inconstant pyramidal lobe may project upwards form the isthmus (Left of the midline) Remnant of
the distal part of the thyroglossal duct
Extent & Location
• In the lower part of the front & side of the neck.
• Gland lies against C5-T1 vertebrae / each lobe extends from the oblique
line of the thyroid cartilage to the 4/5th tracheal rings.
• Isthmus overlies 2nd to 4th tracheal rings. (Palpable)
• Lobes not palpable (because of the tension of the strap muscles)
Capsules & ligaments
• Has 2 capsules.
• True capsule
Derived from peripheral condensation of the connective tissue.
A dense venous plexus lies deep to the this capsule.
• False capsule
Derived from pretracheal Fascia.
Thick along the posterior border where it forms suspensory ligament of Berry where it connects the
lobes to the cricoid cartilage. The recurrent laryngeal nerve is closely related to this ligament.
, Clinical correlations
• During thyroidectomy, removal of the thyroid gland, the gland is removed with the true
capsule to avoid haemorrhages.
Prostate gland also have a true capsule and a false capsule. But in prostate gland, the venous
plexus lies in between the 2 capsules. Therefore, in prostatectomy both capsules are left behind.
Arterial supply
• 2nd most vascular organ
1. Superior thyroid artery.
• The 1st anterior branch of external carotid artery
• Close relation to external laryngeal nerve away from gland.
• At the upper pole divides into anterior and posterior branches.
• Divides into branches after piercing false capsule
• External laryngeal nerve deviates at the apex of a lobe of the gland. Therefore, during thyroidectomy
superior thyroid artery is ligated near the gland
• Anterior branch anastomoses with the same branch of opposite side.
2. Inferior thyroid artery.
• Branch of thyrocervical trunk
• Passes behind the carotid sheath and middle cervical sympathetic ganglion & in front of the vertebral
vessels.
• Close relation to recurrent laryngeal nerve near the gland. Individual branches are ligated to maintain
the blood supply to parathyroid gland.
• Divides into branches before piercing false capsule.
• Ascending branch anastomoses with posterior branch of superior thyroid artery.
3.Additional supply
• Thyroidea ima artery (brachiocephalic or arch of aorta) (about 3% of population)
• Oesophageal and tracheal branches (accessory thyroid arteries).
• Clinical correlations,
During thyroidectomy, the superior thyroid artery is ligated near the gland to save external laryngeal
nerve while the inferior thyroid artery is ligated distal to the gland to save recurrent laryngeal nerve.
• Superior thyroid artery reaches the upper pole of the gland and anastomosis with the opposite artery
along the upper border of the isthmus.
• Inferior thyroid artery reaches the lower pole.
Deep Neck Page 6
Anatomy ©2020 A/L Batch Repeat Campaign
