1. The thyroid gland

2. The thyroid gland Lobes Position Blood supply Development
Parathyroid glands
Tracheostomy
Related topic
Plan of the neck

3. The thyroid gland derives its name from the thyroid cartilage which resembles a shield
(G. thyreos = shield)

4. Function
The thyroid gland is an endocrine gland that is responsible for the secretion of thyroxin and thyrocalcitonin

5. Lobes
The thyroid gland consists of two lobes united in front of the second, third and fourth tracheal rings by an isthmus of gland tissue.
isthmus

6. Lobes
Each lobe is pear-shaped consisting of a narrow upper pole and a broader lower pole
upper pole
lower pole

7. Thyroid scan
This nuclear scan uses an injectable radioactive compound. When injected into the bloodstream the compound will be concentrated in the thyroid gland resulting in an image of the gland
The test can be useful in diagnosis of thyroid tumor

8. Position
sternothyroid
sternohyoid
It lies under cover of sternothyroid and sternohyoid muscles on the side of the larynx and trachea

9. Position
thyrohyoid
sternothyroid
cricothyroid
Thyroid, upper pole
The upper pole of the thyroid cannot normally rise above the level of the oblique line of the thyroid cartilage

10. Position The thyroid gland is caught in the pocket of sternothyroid
thyrohyoid
thyroid cartilage
cricothyroid
cricoid
sternothyroid
thyroid

11. Position
The lower pole of the thyroid gland extends along the side of the trachea as low as the sixth tracheal ring 1 2 3 4 5 6

12. esophagus
Because of the proximity of the thyroid gland to the trachea and esophagus, goiter causes compression of the trachea and esophagus resulting in dyspnea and dysphagia respectively

13. Retro-sternal goitre with tracheal deviation

14. Retro-sternal goitre with esophageal deviation

15. Pyramidal lobe
In about 40% of people, there is a small upwards extension of the isthmus called the pyramidal lobe.

16. Levator glandulae thyroidae
The pyramidal lobe may be attached to the hyoid bone by fibrous or muscular tissue (levator glandulae thyroidae).

17. Variations
Bifurcation of the lower end of the pyramidal process, one part going to each lateral lobe

18. Variations
Pyramidal process attached to the left lobe of the gland, isthmus absent.

19. Variations
Both pyramidal process and isthmus are absent.

20. Pre-tracheal fascia
The thyroid gland is surrounded by a fibrous capsule and is enclosed in the pre-tracheal fascia

21. Pre-tracheal fascia
The pre-tracheal fascia attaches the thyroid gland to the trachea and larynx
thus the thyroid moves upwards on swallowing, an important diagnostic feature for lumps in the neck
larynx
thyroid

22. Blood supply The thyroid gland is very vascular
The vessels lie between the capsule and the pre-tracheal fascia.
In some pathological conditions such as thyrotoxicosis, owing to its high vascularity, the blood flow can be heard with a stethoscope as a bruit

23. Thyroid arteries
superior
thyroid a.
The main arteries are the superior and inferior thyroid arteries.
inferior
thyroid a.

24. Superior thyroid artery
external
carotid a.
carotid
bifurcation
Arises from the anterior surface of the external carotid immediately distal to the carotid bifurcation.
Superior thyroid artery

25. Superior thyroid artery
Arches downwards, giving a sternomastoid branch and a superior laryngeal branch that enters the larynx with the nerve of the same name
superior
laryngeal
a. & n.

26. Superior thyroid artery
enters deep to sternothyroid
Superior thyroid vessels
sternothyroid

27. Superior thyroid artery
before reaching the upper pole of the gland, and within the pre-tracheal fascia, it divides into two main branches one for either surface of the gland
posterior
anterior

28. Superior thyroid artery
the posterior branch anastomoses with the inferior thyroid artery
posterior br.
of superior
thyroid a.
inferior
thyroid a.

29. Inferior thyroid artery
Is a branch of the thyrocervical trunk from the subclavian artery.
inferior
thyroid a.
thyrocervical
trunk
subclavian a.

30. Inferior thyroid artery
Ascends and turns medially at the level of the cricoid cartilage to enter the back of the gland some distance above the lower pole.

31. Inferior thyroid artery
The tortuous course of the inferior thyroid artery is due to the fact that in every swallow the thyroid gland ascends a few centimeters and must naturally drag its blood supply with it.
If this artery has no capability to elongate, it would be traumatized

32. Inferior thyroid artery
Divides outside the pre-tracheal fascia into four or five branches that pierce the fascia separately to reach the lower pole of the gland.
Remember that the superior thyroid artery divides within the pretracheal fascia

33. The recurrent laryngeal nerve lies normally behind the branches of the inferior thyroid artery

34. The recurrent laryngeal nerve lies normally behind the branches of the inferior thyroid artery
but it is common for the nerve to pass between the artery branches before they pass through the fascia.

35. The recurrent laryngeal nerve always lies behind the pre-tracheal fascia and if this structure remains intact during thyroidectomy the nerve will not have been divided
inferior thyroid a.
recurrent laryngeal n.

36. Both thyroid arteries are related to nerves which must be avoided when tying the arteries.

37. A little distance behind the superior thyroid artery is the external laryngeal nerve.
superior laryngeal n.
external laryngeal n.
internal laryngeal n.
external laryngeal n.

38. Superior laryngeal nerve variations
vagus
internal
external

39. To avoid injury to the external laryngeal nerve, the superior thyroid artery is ligated and sectioned near the superior pole of the thyroid gland where it is not so closely related to the nerve as it is at its origin.

40. The cricothyroid muscle is paralyzed
Section of the external laryngeal nerve produces weakness of voice, since the vocal fold cannot be tensed.
The cricothyroid muscle is paralyzed
Cricothyroid tenses the vocal cord

41. The recurrent laryngeal nerve has a variable relationship to the inferior thyroid artery
because of its proximity to the inferior thyroid artery and the pre-tracheal fascia it may be injured while ligating the artery during thyroidectomy

42. hence the advisability of ligating the inferior thyroid artery well lateral to the gland before it begins to divide into its terminal branches.
the inferior thyroid artery gives off esophageal and inferior laryngeal branches before its terminal distribution into the thyroid gland
site of
superior
thyroid a.
ligation
site of
inferior
thyroid a.
ligation

43. The variable relationship of the inferior thyroid artery to the recurrent laryngeal nerve makes thyroid surgery a potential risk to normal speech
The recurrent laryngeal nerve supplies all the intrinsic muscles of the larynx

44. it is advisable that a surgeon about to perform a thyroidectomy examines the vocal cords prior to operation, so that if there is any problem postoperatively one knows at least the origin of the lesion.

45. Recurrent laryngeal nerve damage
Is a complication of thyroid surgery that causes paralysis of the vocal cords
When bilateral the voice is almost absent as the two vocal folds cannot be adducted.

46. Recurrent laryngeal nerve damage
A unilateral recurrent laryngeal nerve injury may not be noticed in normal speech but would be very detrimental to a singers career.

47. The thyroid arteries anastomose freely with each other and with tracheal and esophageal arteries.

48. In operations of partial or sub-total thyroidectomy, all four arteries are tied

49. In operations of partial or sub-total thyroidectomy, all but the posterior part of the gland excised
remaining
thyroid
tissue

50. the dangerous anatomy lies in the posterior lateral lobes (recurrent laryngeal nerve and the parathyroid glands)
parathyroid
gland
Recurrent
laryngeal n.

51. The remains of the gland are located alongside the trachea and contain the parathyroid glands, the whole being supplied with blood by the anastomosis

52. Thyroidae ima artery
In about 10% of individuals, an unpaired artery, the thyroidae ima (L. ima = lowest) is a small occasional artery from the brachiocephalic trunk, or left common carotid artery, or direct from the arch of the aorta

53. Thyroidae ima artery
Ascends anterior to trachea and supplies the isthmus of the thyroid gland.

54. Thyroidae ima artery
The possible presence of the thyroid ima artery must be remembered when incising the trachea inferior to the isthmus.
As the thyroidae ima runs anterior to the trachea, it is a potential source of serious bleeding

55. Thyroid veins The veins are three in number on each side
Internal jugular v.
Superior thyroid v.
The veins are three in number on each side
the superior thyroid vein from the upper pole follows the artery and enters the internal jugular vein or the common facial vein

56. Thyroid veins
Internal jugular v.
The middle thyroid vein is short and wide, it enters the internal jugular vein
middle thyroid v.

57. Thyroid veins
From the isthmus and lower pole of the gland the inferior thyroid veins form a plexus within the pre-tracheal fascia that descends in front of the trachea to reach the left brachiocephalic vein
inferior thyroid vv.
brachiocephalic v.

58. Inferior thyroid veins
As the inferior thyroid veins cover the anterior surface of the trachea inferior to isthmus, they are potential sources of bleeding during tracheotomy (also remember the situation of the thyroidae ima artery).

59. Development of the thyroid gland
The gland begins as a diverticulum from the floor of the embryonic pharynx

60. Development of the thyroid gland
The diverticulum grows caudally superficial to the hyoid before dividing into two lobes
The stem of the diverticulum, the thyroglossal duct, normally disappears
hyoid
Thyroglossal duct

61. Development of the thyroid gland
After the tongue has developed, it can be seen that the point of outgrowth of the thyroglossal duct is the foramen cecum (of Morgagni) [Morgagni, Giovanni Battista, , a Padua anatomist and pathologist, also known for hydatid of Morgagni (appendix testis) and anal columns (of Morgagni)].

62. Thyroglossal cyst
cysts derived from the duct may also appear anywhere between the foramen cecum and the normal position in the midline of the neck
Beneath foramen cecum
Floor of the mouth
Suprahyoid
Subhyoid
On thyroid cartilage
At level of cricoid cartilage

63. Thyroglossal cyst
Can be diagnosed because characteristically it moves upwards as the patient puts his tongue out.

64. Infection of a thyroglossal cyst may spread to a persistent thyroglossal duct which must be then excised

65. Although the duct lies ventral to the hyoid bone, it passes up for a short distance behind the body, which therefore has to be excised with the duct

66. Accessory thyroid gland
Aberrant thyroid tissue may appear between the foramen cecum and the normal position

67. Lingual thyroid
Rarely the thyroid fails to descend during development resulting in the development of a lingual thyroid

68. Ectopic thyroid
Failure of descent mar result in a superior cervical thyroid in the region of the hyoid bone
the thyroid may sometimes descended too far and be found in the superior mediastinum

69. Parathyroid glands Two on each side
They are yellow-brown endocrine glands, about the size of a small pea (about 0.5x0.8 cm ovoids)
They are important because of their role in calcium metabolism. They secrete parathormone that mobilizes bone calcium and increases gut and kidney calcium absorption

70. Parathyroid glands
Are located posterior to the thyroid gland between its capsule and fascial sheath

71. Superior parathyroid glands
more constant in position
embedded in the posterior surface of the thyroid gland, a short distance above the entry of inferior thyroid artery (and the level of the cricoid cartilage).

72. Inferior parathyroid glands
variable in position
usually embedded behind the lower pole but is often found elsewhere (they may even present in the superior mediastinum).

73. Parathyroid development
The parathyroids develop from the endoderm of the third (inferior gland) and fourth (superior gland) pharyngeal pouches

74. Parathyroid development
The thymus also develops from the third pouch and may therefore carry the inferior parathyroid with it when it descends into the thorax.

75. Parathyroid glands, blood supply
The glands are usually supplied by the inferior thyroid arteries but may also be supplied by both superior and inferior thyroid arteries
posterior br.
of superior
thyroid a.
inferior
thyroid a.

76. Parathyroid glands
Awareness of the close relationship between the parathyroid glands and the thyroid gland is essential to prevent removal or damage of the parathyroid glands during thyroidectomy.

77. The parathyroid glands are usually safe during subtotal thyroidectomy because the posterior part of the thyroid gland is preserved

78. The variability in position of the parathyroid glands may create a problem during total thyroidectomy; in this case the parathyroid glands are saved by following their small vessels which are kept intact before the thyroid is removed.

79. Tracheostomy
Endotracheal tube
When tracheostomy is done electively after establishing an airway with an endotracheal tube, a short transverse incision is made one cm below the cricoid cartilage

80. Tracheostomy
The transverse incision is made midway between the cricoid cartilage and the sternal notch

81. Tracheostomy
The decussating fibers of platysma are divided.

82. Tracheostomy
After elevating platysma, the investing fascia between the strap muscles is incised

83. Tracheostomy
The pretracheal (strap) muscles are seperated

84. Tracheostomy The pretracheal fascia is split longitudinally
The thyroid isthmus is divided and sutured

85. Tracheostomy
The second tracheal ring is precisely identified and divided vertically in the midline, extending the incision through the third ring in most cases
The first ring is preserved

86. Tracheostomy A thyroid retractor gently spreads the tracheal opening.
The tracheostomy tube with obturator is introduced after withdrawing the endotracheal tube under direct vision to a point just above the stoma
Tracheostomy tube
retractor
Endotracheal tube

87. Tracheostomy
Tracheostomy tube flange
If more room is needed, the fourth ring may be partially divided
A transverse incision is to be avoided.
The skin is closed loosely
The flange of the tracheostomy tube not only is tied with a tape around the neck but also is sutured to the skin.
4th tracheal ring

88. Tracheostomy
The endotracheal tube is removed only when the tracheostomy tube has been shown to provide a satisfactory airway
If there is any question about where the tip of the tube lies, a flexible bronchoscope may be used to check the distal position.

89. Tracheostomy
The tracheostomy tube should be just large enough to provide an adequate airway for the patient. Larger tubes can only cause damage.
It must be remembered that most women, even when obese, have tracheas smaller in diameter than those of men

90. Permanent tracheostomy opening

91. Complications of tracheostomy
the anterior jugular veins may be encountered as the superficial fascia is incised
They are avoided by maintaining a midline position

92. Complications of tracheostomy
Sometimes a large jugular venous arch may be encountered

93. Complications of tracheostomy
The inferior thyroid veins are often asymmetric, hence more liable to injury

94. Complications of tracheostomy
The branches of the superior and inferior thyroid arteries may anastomose across the midline

95. Complications of tracheostomy
A thyroid ima artery is very occasionally present and must be ligated if found

96. Complications of tracheostomy
The brachiocephalic artery and vein may be injured if sharp dissection is carried too far downwards
The artery may be eroded by a tracheostomy tube, resulting in a tracheo-arterial fistula

97. Complications of tracheostomy
In children the left brachiocephalic vein and the thymus may extend above the suprasternal notch.

98. Complications of tracheostomy
Tube too curved
Tube too low
The subclavian artery and vein may be compromised by a tracheostomy to that is incorrectly curved or is placed too low

99. Complications of tracheostomy
The existence of fascial planes predisposes to surgical emphysema, particularly if the skin is sutured too tightly.
Investing fascia

100. Complications of tracheostomy
Surgical emphysema may extend into the mediastinum.
Investing
fascia
pretracheal
fascia

101. Complications of tracheostomy
Skin & superficial fascia
Beware of over-enthusiastic incision into the trachea; the esophagus is immediately posterior.
Investing fascia
Thyroid & pretracheal fascia
trachea
esophagus