4. The gland begins
as a diverticulum
[median
endodermal thyroid
diverticulum] from
the floor of the
embryonic pharynx.
5. The diverticulum
grows caudally
superficial to the
hyoid before dividing
into two lobes
The stem of the
diverticulum, the
thyroglossal duct,
normally disappears.
Thyroglossal duct
6. After the tongue has developed, it
can be seen that the point of
outgrowth of the thyroglossal
duct is the foramen cecum (of
Morgagni).
Developmental anomalies-
TG duct cyst or fistula [d/d]
Ectopic thyroid
Lingual thyroid
7. The lobes of the thyroid
contain many hollow,
spherical structure called
follicles, which are the
functional units of the
thyroid gland.
Interspersed between the
follicles are C cells, which
secrete calcitonin.
Each follicle is filled with
a thick sticky substance
called colloid.
8. Butterfly/H shaped
Lobes 5*3*2cm
Isthmus 1.2*1.2cm
Weight 25g in adult
Larger in females
Physiologically enlarges in pregnancy &
menstruation.
9. Location:
lower part of the front and
side of the neck opposite to
the C5, C6, C7 and T1
vertebrae.
Each lateral lobe extends
upwards to oblique line of
thyroid cartilage and below
up to the 5th or 6th tracheal
ring.
The isthmus extends across
the midline in front of the
2nd ,3rd and 4th tracheal ring.
10. T1 / 4th or 5th
tracheal ring
C5
Isthumus 2nd -
4th tracheal ring
11. True capsule (fibrous) – peripheral
condensation of connective tissue of gland.
forms septae & lobules
Arteries and venous plexus of veins lies deep
to it.
Sx importance- To avoid haemorrhage during
operation the thyroid removed along with
true capsule.
12. False capsule –
Pretracheal layer of deep cervical fasvia fascia
Moves during deglutition.
Clinical importance- To differentiate thyroid swelling
from other neck swelling.
[other structures are TG cyst, subhyoid bursa, pre/para
tracheal LN, extrinsic carcinoma of larynx]
Forms Posterior Suspensory ligament
[Ligamentum Berry*]
13.
14. 1. Lobes
Conical
Apex, base
3 surfaces – L, M, PL
2 borders – A, P
Apex – oblique line of thyroid cartilage*
Base – 4th/5th tracheal ring
15. The thyroid gland
consists of two
lobes united in
front of the second,
third and fourth
tracheal rings by an
isthmus of gland
tissue.
16. Each lobe is pear-
shaped consisting
of a narrow upper
pole [apex] and a
broader lower pole
[base]
upper pole
lower pole
17. • It is the posterior extension of lateral lobes.
• It is found in approx. 60-70% of people.
Whenever found the recurrent laryngeal
nerve is usually deep to it.
• More common in right side
18. It lies under cover of sternothyroid
and sternohyoid muscles on the
side of the larynx and trachea.
19. The thyroid gland
is caught in the
pocket of
sternothyroid.
cricothyroid
thyroidcartilage
thyrohyoid
sternothyroid
THYROID
GLAND
20. The lower pole of the
thyroid gland
extends along the
side of the trachea as
low as the sixth
tracheal ring.
21. Because of the proximity of the thyroid gland to the
trachea and esophagus, goiter causes compression of
the trachea and esophagus resulting in dyspnoea and
dysphasia respectively .
22. Lateral surface – convex,
Covered with sternohyoid, SCM,
superior belly of omohyoid,
sternothyroid
25. In about 40% of
people, there is a
small upwards
extension of the
isthmus called the
pyramidal lobe.
Usually from left
side.
26. The pyramidal lobe
may be attached to
the hyoid bone by
fibrous or muscular
tissue (levator
glandulae
thyroidae).
27. The thyroid gland
is surrounded by a
fibrous capsule and
is enclosed in the
pre-tracheal fascia.
28. 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 .
29. The thyroid gland is highly
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
31. Arises from the
anterior surface of
the external carotid
immediately distal to
the carotid
bifurcation.
[ 1st anterior branch
of external carotid
artery ]
32. Arches downwards,
giving a
sternomastoid
branch and a
superior laryngeal
branch that enters
the larynx with the
nerve of the same
name.
34. 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
35. The posterior branch
anastomoses with the
inferior thyroid artery
36. 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.
37. Is a branch
of the
thyrocervic
al trunk
from the
subclavian
artery.
38. Ascends and
turns medially
at the level of
the cricoid
cartilage to
enter the back
of the gland
some distance
above the
lower pole.
39. 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.
40. 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
41. The thyroid arteries
anastomose freely
with each other and
with tracheal and
esophageal arteries.
42. Lowest thyroid 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
43. Ascends anterior to
trachea and
supplies the
isthmus of the
thyroid gland.
44. 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 .
45. • The recurrent laryngeal nerves ascend on either side of the trachea
and each lies just lateral to ligament of Berry as it enters the larynx.
• In about 25% of patients, the recurrent laryngeal nerve is contained
within the ligament as it enters the larynx.
• Right recurrent laryngeal nerve originates from the vagus nerve as it
crosses the subclavian artery; it then passes posterior to the
subclavian artery and ascends in a position lateral to the trachea
along the tracheoesophageal groove.
• Right recurrent laryngeal nerve can usually be found no further than
1 cm lateral to or within the tracheoesophageal groove, at the level
of the lower border of the thyroid.
46. • At midportion of thyroid the nerve might divide into one, two,
or more branches as it enters the first or second ring of the
trachea, with the most important branch disappearing
beneath the inferior border of the cricothyroid muscle. The
nerve can usually be found immediately anterior or posterior
to a main arterial trunk of the inferior thyroid artery at this
level.
• Left side, the recurrent laryngeal nerve separates from the
vagus as that nerve traverses the arch of the aorta.
47. • It passes inferiorly and medially to the
aorta at the ligamentum arteriosum
and begins to ascend toward the
larynx, where it enters the
tracheoesophageal groove as it
ascends to the level of the lower lobe
of the thyroid.
• A small branch of the inferior
laryngeal artery crosses the nerve at
the level of the ligament of Berry, so
bleeding in this area should be
addressed with great caution to avoid
nerve injury.
48. NON-RECURRENT LARYNGEAL NERVE
• A nonrecurrent right laryngeal nerve can arise directly from the vagus
• It is an anomalous RLN.
• It does not have recurrent course.
• After origin runs directly medially into the larynx.
• Mostly founds in right side.
• This nonrecurrent anatomy is found in 0.5% to 1.5% of patients and
associated with anomalous right SCA which is in such cases arise from
left side of descending aorta and retro-oesophagial ccurs
• A nonrecurrent left laryngeal nerve is associated with more extensive
anomalies and it is very rare.
49. Location of recurrent laryngeal nerve:
Anatomically the course of recurrent laryngeal nerve is highly
variable. It is commonly sought in the tracheo oesophageal groove
in between the branches of inferior thyroid artery.
• The inferior thyroid artery is a branch of thyrocervical trunk on the
right side. It enters the neck by piercing the prevertebral fascia
medial to the carotid sheath to enter the posterior part of thyroid
gland. During it makes sense to identify the recurrent laryngeal
nerve before dividing the branches of inferior thyroid artery
• Most accurate and safe way of identifying the nerve is to seek it low
down in the tracheo - oesophageal groove. Here it forms the third
side of Beahr's triangle. This triangle is named after OH
Beahrs. The other two sides of the triangle are formed by the
common carotid and inferior thyroid artery
50.
51. 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.
52. This variable branching pattern (of the nerve and the arterial system) limits
the ability of the surgeon to rely solely on the ITA as a landmark to identify
the nerve.
The one constant is the intimate relationship of the ITA to the RLN; most
investigators recommend identifying the nerve before ligating the artery to
prevent inadvertent injury to the nerve.
To avoid the difficulty in identifying the nerve in this region, some surgeons
advocated identifying the RLN above the thoracic inlet and following it
cephalic into the larynx, whereas others advocated identification of the
nerve at the cricothyroid joint where it enters the larynx.
Weisberg et al stated that the right RLN is at a higher risk for stretch injuries
during cervical spine surgeries because of its lateral position relative to the
TE groove.
53. 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.
54. • Superior Laryngeal Nerve
• Originates from the vagus nerve at the base of the
skull and descends toward the superior pole of the
thyroid along the internal carotid artery
• At the level of the hyoid cornu, it divides into
external and internal branches
• external branch continues to travel along the lateral
surface of the inferior pharyngeal constrictor muscle
and usually descends anteriorly and medially, along
with the superior thyroid artery
• With in1 cm of the entrance of the superior thyroid
artery into the thyroid capsule, the nerve generally
takes a medial course and enters the cricothyroid
muscle
• Damage to the external branch can result in severe
loss of voice quality or strength.
55. • Triangle in which external laryngeal
nerve is identified during thyroid
surgery.Boundaries are
• Laterally by upper pole of thyroid and
superior thyroid vessels.
• Superiorly by the attachments of strap
muscles and deep investing layer of
fascia to the hyoid
• Medially by the midline
• Floor by cricothyroid muscle
• Roof the strap muscles
• External branch of RLN lies within this
triangle.
56.
57. • Relationship of the External Laryngeal Nerve And Superior
Thyroid Artery extremely variable, and a new classification of
the distribution of the nerve has been proposed by Cernea
Classified into:-
• type 1 anatomy, the nerve crosses the superior thyroid vessels =
1 cm above the superior thyroid pole
• type 2a, nerve crosses the superior thyroid vessels <1cm the
superior thyroid pole
• The type 2b occurs in 14% to 20% of normal individuals. It
crosses the avascular space below the tip of the superior thyroid
pole and is at particularly high risk of injury. Interestingly, the
incidence of this type of nerve has been noted to be much
higher (up to 56%) in patients with large goiters
58.
59. More recently Friedman et al [9] analyzed 1057 SLN explored at
the time of thyroidectomy.
They proposed a classification system with three anatomic
variations, type 1 with the nerve running superficial to the
inferior constrictor muscle,
type 2 with the nerve penetrating the lower part of the inferior
constrictor,
type 3 whereby the nerve penetrates the superior aspect of the
inferior constrictor muscle and remains covered by the muscle
on its course to the crico-thyroid muscle.
This classification focuses on the distal aspect of the SLN as
opposed to other systems that look at the intimate relationship
between the SLNE and the STA.
Regardless of the classification system, it is clear that the SLNE
travels in close proximity to the STA (approximately 20% to 60%
within 1 cm STA and superior thyroid pole) and must be
protected by the surgeon.
60. Both thyroid arteries are
related to nerves which must
be avoided when tying the
arteries.
61. 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
62. 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.
63. 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.
64. The variable relationship of the inferior
thyroid artery to the recurrent laryngeal
nerve makes thyroid surgery a potential
risk to normal speech
65. 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
Superior thyroid veins
Internal jugular v.
brachiocephalic v.
66. The middle thyroid
veins is short and
wide, it enters the
internal jugular
vein
middle thyroid v.
Internal jugular v.
67. Internal jugular v.
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.
68. As the inferior thyroid
veins cover the anterior
surface of the trachea
inferior to isthmus, they
are potential sources of
bleeding during
tracheostomy (also
remember the situation of
the thyroidae ima artery).
Kocher’s vein
4th thyroid vien
69. Vasoconstrictor sympathetic innervation
Mainly from Middle Cervical Gangliaon.
Partly from SCG and ICG.
Cardiac and laryngeal branches of
vagus(parasympathetic)
Enter along with blood vessels
Never secretomotor (secretion regulated by TSH)
70. The lymphatic vessels of the thyroid gland drain into:
1) Pretracheal lymph nodes.
2) Paratracheal lymph nodes.
- The efferent of these nodes drain into
the deep cervical lymph nodes.
71. Extensive, multidirectional flow
periglandular prelaryngeal (Delphian)
pretracheal paratracheal (along RLN)
brachiocephalic (sup mediastinum) deep cervical
thoracic duct
Upper part via prelaryngeal LN to upper deep CLN
Lower part via pretracheal and paratracheal LN to lower
deep CLN
Brachiocephalic LN and thoracic duct
regional metastasis of thyroid carcinoma are superior
and lateral, along IJV ie: invasion of the pretracheal
and paratracheal LNs and obstruction of normal lymph
flow
72.
73.
74. PARA THYROID GLANDS
Small bean shaped structures with a yellow-tan to
caramel color and usually four in number.
Size 6×4×2mm
Weight each 50mg.
The identification and preservation of the parathyroid
glands during thyroid surgery is of upmost
importance.
The superior parathyroids are most consistently
located (80%) within 1cm superior to the intersection
of the RLN and the ITA (near the cricothyroid (CT)
joint). The inferior parathyroids are more variable in
their location because of the longer migration with
inferior thyroid and thymus.
75. Superior parathyroid is located above the ITA
and posterior to RLN , close to cricoid cartilage
along posterior border of thyroid gland.
Inferior parathyroid is located below the level of
ITA and usually anterior to RLN.
However inferior parathyroid may be located
anywhere from hyoid above to superior
mediastinum below because it descent along
with thymus gland.
76. From a surgical viewpoint, the parathyroids must be
identified and preserved with an intact blood supply.
A medial to lateral dissection is utilized with the plane of
dissection along the thyroid capsule.
The parathyroids are identified in the typical locations (as
described above).
This medial to lateral dissection allows identification and
mobilization away from the thyroid while preserving the
blood supply
77. From a surgical viewpoint there are a number of critical
anatomic structures that lie in close proximity to the
thyroid gland.
These critical structures include the recurrent laryngeal
nerves, the superior laryngeal nerves, and the parathyroid
glands.
Successful thyroid surgery depends on the technical skill of
the surgeon to identify and preserve these vital structures.
