*Thyroid Gland – Anatomy** **Location* * Located in the **anterior neck**, below the **larynx**. * Lies over the **trachea**, from the level of **C5 to T1 vertebrae**. *Structure** Bilobed gland**: Right and left lobes connected by a thin bridge called the **isthmus**. * Sometimes a pyramidal lobe is present (remnant of thyroglossal duct). **Size & Weight** * ~4-6 cm in length. * Weighs about **15–25 grams** in adults. **Capsules** * **True capsule**: Thin fibrous capsule. * **False capsule**: Formed by the pretracheal fascia. *Blood Supply** *Arterial supply**: * **Superior thyroid artery** (from external carotid) * **Inferior thyroid artery** (from thyrocervical trunk) * Occasionally: **Thyroid ima artery** (from brachiocephalic trunk or aorta) * **Venous drainage**: * **Superior**, **middle**, and **inferior thyroid veins** → drain into internal jugular and brachiocephalic veins. **Lymphatic Drainage** * Prelaryngeal, pretracheal, and paratracheal lymph nodes → deep cervical nodes. Nerve Supply** Sympathetic**: Cervical sympathetic ganglia (vasomotor). Parasympathetic**: From the vagus nerve** (via recurrent laryngeal and external laryngeal nerves). * Recurrent laryngeal nerve runs close to the thyroid — important surgically. **Development** * Develops from a **midline endodermal outgrowth** of the **floor of the pharynx** (foramen cecum). * Migrates downward via the **thyroglossal duct** (normally obliterated).

1. Lecture By
Dr.N.Mugunthan.MS,DNB,MNAMS,PhD, MBA (Hosp.Adm.)
Professor of Preclinical Sciences,
KMMC

2. Competencies
Compete
ncy No.
Topic- Deep structures in the neck Domain Level Core
AN 35.2 Describe the parts, borders, surfaces,
contents, relations and nerve supply
of parotid gland with course of its duct
and surgical importance.
K KH Y
AN 35.8 Describe the anatomically relevant
clinical features of Thyroid
swellings
K KH Y
AN 43.2 Describe and draw the
microanatomical features of thyroid
K KH Y
AN 43.4 Describe the development and
developmental basis of congenital
anomalies of thyroid gland
K KH Y
© Dr.N.Mugunthan

3. Specific Learning Objectives
At the end of this lecture, Phase –I MBBS students should be
able to answer the questions asked in the case scenario
A 50 years old female visited to her primary
care physician with complaints of painless
swelling in front of neck in the midline since
last 6 months, weight & hair loss,
nervousness and eye pressure. She has no
other medical problems, but some of her
family members have similar symptoms and
taking medication.
On examination, a butterfly shaped swelling
moves with deglutition and lower margin of
swelling can be visualized on deglutition,
exophthalmos, an enlarged non-tender goiter,
hyperreflexia and a tremor when her arms
are outstretched. © Dr.N.Mugunthan

4. On the basis of your knowledge in anatomy answer
the following questions:
1. What is the probable clinical condition ?
2. State the reason why the thyroid swelling moves
with deglutition.
3. Describe the thyroid gland under following
headings: a) Coverings b) Presenting parts
c)Relations d) Applied anatomy
4. Name the arteries supplying the thyroid gland.
5. Name the structures accompanying which can be
injured while ligating the arteries during
thyroidectomy.
Specific Learning Objectives cont…
© Dr.N.Mugunthan

5. Overview
Thyroid gland
Situation & extent
Coverings
Presenting parts & its description
Relations
Blood supply
Lymphatic drainage
Nerve supply
Applied aspects
Microstructure
Development
© Dr.N.Mugunthan

6. MIDLINE STRUCTURES IN THE NECK
© Dr.N.Mugunthan

7. MIDLINE STRUCTURES IN THE NECK
© Dr.N.Mugunthan

8. MIDLINE STRUCTURES IN THE NECK
© Dr.N.Mugunthan

9. MIDLINE STRUCTURES IN THE NECK
© Dr.N.Mugunthan

10. MIDLINE STRUCTURES IN THE NECK
© Dr.N.Mugunthan

11. MIDLINE STRUCTURES IN THE NECK
© Dr.N.Mugunthan

12. MIDLINE STRUCTURES IN THE NECK
© Dr.N.Mugunthan

13. THYROID GLAND
Definition:
Endocrine gland
Highly vascular
Yellowish brown in
colour
Synthesis, stores &
releases thyroid
hormone (T3 & T4)
© Dr.N.Mugunthan

14. SHAPE
Butterfly or
H shaped
2 lateral lobes
connected by
Isthmus
© Dr.N.Mugunthan

15. SITUATION & EXTENT
Front & sides of neck
Deep to the floor of
muscular triangle
Opp. C5,C6,C7 & T1
Extent:
Each lobe – middle of
thyroid cartilage to 5th
tracheal ring
Isthmus – 2nd,3rd & 4th
tracheal ring
© Dr.N.Mugunthan

16. MEASUREMENTS
Each lobe :
5cm X 3cm X 2cm
Isthmus :
1.2cm X 1.2cm
Weight (average): 25g
F > M
Size increases during
pregnancy &
menstruation © Dr.N.Mugunthan

17. COVERINGS
2capsule:
1. Outer false capsule –
(splitting of pretracheal
fascia)
Thick on inner (medial)
surface of gland – forms
suspensory lig.of Berry
Suspensory lig.of Berry
connects the lobe with
cricoid cartilage
© Dr.N.Mugunthan

18. WHY DOES THYROID GLAND MOVES WITH
DEGLUTITION ?
1. Attachment of
pretracheal fascia (form
false capsule) from body
of hyoid bone to oblique
line of thyroid cartilage
2. Suspensory lig.of Berry
connects the lobe with
cricoid cartilage
© Dr.N.Mugunthan

19. THYROID GLAND MOVES WITH DEGLUTITION
WHY ?
Attachment of
pretracheal fascia (form
false capsule) from body
of hyoid bone to oblique
line of thyroid cartilage
Suspensory lig.of Berry
connects the lobe with
cricoid cartilage
© Dr.N.Mugunthan

20. 2. Inner true capsule –
condensation of
fibrous stroma of gland
Deep to true capsule –
dense capillary plexus.
During thyroidectomy
– remove the gland
with capsule ( compare
with prostate)
COVERINGS cont…..
© Dr.N.Mugunthan

21. PRESENTING PARTS
1. Two lateral lobes
2. Isthmus (connecting 2 lateral lobes)
Lateral lobe :
Pyramidal in shape
• Apex
• Base
2 borders:
i. Anterior border
ii. Posterior border
3 surfaces:
i. Anterolateral surface
ii. Posterolateral surface
iii. Medial surface © Dr.N.Mugunthan

22. RELATIONS OF LATERAL LOBE
Apex:
Directed upwards towards
oblique line of thyroid
cartilage
Sandwiched between
inferior constrictor &
sternothyroid
Thyroid enlargement cannot
extend above
Related to sup.thyroid artery
& ext.laryngeal nerve
(ligate the artery close to
gland) © Dr.N.Mugunthan

23. BASE
Extends 5th or 6th tracheal
ring (T1)
Related to inf.thyroid
artery & recurrent
laryngeal nerve
(Ligate the artery away
from the gland)
© Dr.N.Mugunthan

24. ANTEROLATERAL (SUPERFICIAL) SURFACE
Overlapped by
infrahyoid muscles
( Within outwards )
o Sternothyroid
o Sternohyoid
o Superior belly of
omohyoid
o Sternomastoid (partly)
© Dr.N.Mugunthan

25. ANTEROLATERAL (SUPERFICIAL) SURFACE
Overlapped by
infrahyoid muscles
( Within outwards )
o Sternothyroid
o Sternohyoid
o Superior belly of
omohyoid
o Sternomastoid (partly)
© Dr.N.Mugunthan

26. ANTEROLATERAL (SUPERFICIAL) SURFACE
Overlapped by
infrahyoid muscles
( Within outwards )
o Sternothyroid
o Sternohyoid
o Superior belly of
omohyoid
o Sternomastoid (partly)
© Dr.N.Mugunthan

27. ANTEROLATERAL (SUPERFICIAL) SURFACE
Overlapped by
infrahyoid muscles
( Within outwards )
o Sternothyroid
o Sternohyoid
o Superior belly of
omohyoid
o Sternomastoid (partly)
© Dr.N.Mugunthan

28. ANTEROLATERAL (SUPERFICIAL) SURFACE
Overlapped by
infrahyoid muscles
( Within outwards )
o Sternothyroid
o Sternohyoid
o Superior belly of
omohyoid
o Sternomastoid (partly)
© Dr.N.Mugunthan

29. MEDIAL (DEEP) SURFACE
Related to -
2 tubes, 2 nerves, 2
muscles & 2 cartilages
2 tubes – larynx &trachea ,
pharynx & oesophagus
2 nerves- external &
recurrent laryngeal nerves
2 muscles-cricothyroid &
inferior constrictor
2 cartilages- thyroid &
cricoid
© Dr.N.Mugunthan

30. POSTEROLATERAL SURFACE
Related to carotid sheath
& its contents
Ansa cervicalis infront of
carotid sheath
Carotid sheath
Contents:
1. CCA & ICA
2. IJV
3. Vagus nerve
Sympathetic chain
behind the sheath
© Dr.N.Mugunthan

31. ANTERIOR BORDER
Separates anterolateral
surface from medial
surface
Related to anterior branch
of superior thyroid artery
© Dr.N.Mugunthan

32. POSTERIOR BORDER
Separates medial surface
from posterolateral surface
Related to:
 Anastomosis of sup. & inf.
thyroid arteries
 Parathyroid glands (superior
& inferior)
[Sup. parathyroid at the level
of C6 (cricoid)
Inf. parathyroid at lower pole
of gland]
 On left side thoracic duct
(lower part)
© Dr.N.Mugunthan

33. ISTHMUS
Connects both lateral
lobes across midline
Presents 2 surfaces 2
borders:
2 Surfaces:
1. Anterior surface
2. Posterior surface
 2 Borders:
1. Superior border
2. Inferior border
© Dr.N.Mugunthan

34. ANTERIOR SURFACE
Related to :-
Skin
Superficial fascia &
ant.jugular vein
Investing layer of deep
cervical fascia
Sternothyroid &
sternohyoid
© Dr.N.Mugunthan

35. POSTERIOR SURFACE
Related to :
2nd,3rd & 4th tracheal
rings
© Dr.N.Mugunthan

36. SUPERIOR BORDER
Anastomosis between 2
sup.thyroid arteries
Pyramidal lobe
(occasionally from
isthmus)
Levator glanduli thyroidae
– fibromuscular band
Extend from hyoid bone to
isthmus or pyramidal lobe
(Striated muscle in levator
glanduli thyroidae –
supplied by ext.laryngeal
nerve ) © Dr.N.Mugunthan

37. INFERIOR BORDER
Inferior thyroid veins
Arteria thyroidea ima
(if present)
© Dr.N.Mugunthan

38. BLOOD SUPPLY
Arterial supply:
1. Superior thyroid artery
(from ext.carotid artery)
Accompanied by external
laryngeal nerve
Ligate the artery close to
gland to avoid injury to this
nerve
(nerve is more intimately
related to artery a little
away from gland)
© Dr.N.Mugunthan

39. ARTERIAL SUPPLY cont….
2. Inferior thyroid artery
(from thyrocervical trunk)
Accompanied by recurrent
laryngeal nerve
Ligate the artery away from
the gland to avoid injury to
this nerve
(recurrent laryngeal nerve
cross infront of inf.thyroid
artery close to gland)
© Dr.N.Mugunthan

40. 3. Arteria thyroidea ima –
occasionally (from arch
of aorta or
brachiocephalic trunk)
4. Numerous accessory
thyroid arteries ( from
tracheal & oesophageal
branches)
ARTERIAL SUPPLY cont….
© Dr.N.Mugunthan

41. SUPERIOR & INFERIOR THYROID ARTERIES
©Prof. Dr.N.Mugunthan

42. VENOUS DRAINAGE
Veins do not accompany the
arteries
 Arise from venous plexus
deep to true capsule
1. Sup.Thyroid vein (drains
into IJV)
2. Middle thyroid vein (drains
into IJV)
3. A bunch of inf.thyroid vein
drains into left
Brachiocephalic vein
4. Occasionally fourth thyroid
vein (Kocher’s vein) drains
into IJV
© Dr.N.Mugunthan

43. LYMPHATIC DRAINAGE
Upper medial portion –
prelaryngeal nodes
Lower medial portion –
pretracheal nodes
Upper lateral portion –
upper deep cervical nodes
Lower lateral portion –
lower deep cervical nodes
© Dr.N.Mugunthan

44. NERVE SUPPLY
1. Sympathetic nerves
2. Parasympathetic nerves
Sympathetic nerves:
From superior, middle &
inferior cervical ganglion
Vasomotor supply
Parasympathetic nerves:
From vagus & recurrent
laryngeal nerves
© Dr.N.Mugunthan

45. APPLIED ANATOMY
© Dr.N.Mugunthan

46. DEVELOPMENT OF THYROID GLAND
2 sources:
1. Median thyroid element
(floor of pharynx ,
endodermal
diverticulum -
Thyroglossal duct)
2. Lateral thyroid rudiment
(caudal pharyngeal
complex - 4th pouch)
© Dr.N.Mugunthan

47. Congenital anomalies
of thyroid:
a. Thyroglossal cyst
b. Thyroglossal fistula
c. Lingual thyroid
d. Retrosternal thyroid
e. Ectopic thyroid
f. Accessory thyroid
APPLIED ANATOMY
© Dr.N.Mugunthan

48. APPLIED ANATOMY cont….
Goitre - enlargement of
thyroid gland (hypo or
hyper function
Hyperthyroidism
(thyrotoxicosis)
Hypothyroidism
(myxoedema in adult &
cretinism in children)
Carcinoma of thyroid
gland
© Dr.N.Mugunthan

49. Carcinoma of thyroid
symptoms ( due to
compression)
Larynx/trachea –
dyspnoea
Pharynx/oesophagus –
dysphagia
Involvement of external &
recurrent laryngeal nerve
– hoarseness of voice
APPLIED ANATOMY cont….
© Dr.N.Mugunthan

50. Investigation:
 Thyroid function test
 Thyroid scan (ultra sound)
 Radioisotope scan using
Iodine 131(hot & cold nodule)
 Radionuclide scan
(Technetium)
 FNAC (fine needle aspiration
cytology)
Treatment: (medical & surgical)
Thyroidectomy
 Total thyroidectomy
 Subtotal thyroidectomy
 Hemithyroidectomy
APPLIED ANATOMY cont….
© Dr.N.Mugunthan

51. During thyroidectomy –
Ligate the sup.thyroid
artery close to apex of
gland to avoid injury to
ext.laryngeal nerve
Ligate the inf.thyroid
artery away from base of
gland to avoid injury to
recurrent laryngeal nerve
APPLIED ANATOMY cont….
© Dr.N.Mugunthan

52. During thyroidectomy –
To release the gland
suspensory lig.of Berry
should be cut.
While cutting avoid injury
to recurrent laryngeal
nerve (related post. to lig
of Berry)
Look for arteria thyroidea
ima
Look for Kocher’s vein (4th
vein)
APPLIED ANATOMY cont….
© Dr.N.Mugunthan

53. During thyroidectomy –
Accidental removal of
parathyroid -
hypoparathyroidism
(hypocalcaemia)
Carpopedal
spasm,convulsions &
neurovascular irritability
To avoid this, posterior part
of lateral lobe of thyroid
gland should be left behind
(to preserve parathyroid)
APPLIED ANATOMY cont….
© Dr.N.Mugunthan

54. Thyroid follicle at different levels
of activity
State of
the
follicle
Lining
epithelium
Amount of
colloid
Inactive/
Resting
Squamous Abundant
Active Cuboid Moderate
Highly
Active
Low
Columnar
Scanty
© Dr.N.Mugunthan

55. Parafollicular C cells
O Polyhedral cells with oval
nucleus
O Paler & larger than thyroid
follicular cells
O Present between basement
membrane and the
follicular cell
O Secretes - Thyrocalcitonin
[lowers the blood calcium
level]
© Dr.N.Mugunthan

56. Virtual Microscope –Thyroid gland

57. Specific Learning Objectives
At the end of this lecture, Phase –I MBBS students should be
able to answer the questions asked in the case scenario
A 50 years old female visited to her primary
care physician with complaints of painless
swelling in front of neck in the midline since
last 6 months, weight & hair loss,
nervousness and eye pressure. She has no
other medical problems, but some of her
family members have similar symptoms and
taking medication.
On examination, a butterfly shaped swelling
moves with deglutition and lower margin of
swelling can be visualized on deglutition,
exophthalmos, an enlarged non-tender goiter,
hyperreflexia and a tremor when her arms
are outstretched. © Dr.N.Mugunthan

58. On the basis of your knowledge in anatomy answer
the following questions:
1. What is the probable clinical condition ? Thyroid
swelling probably “Hyperthyroidism”
2. State the reason why the thyroid swelling moves
with deglutition.
3. Describe the thyroid gland under following
headings: a) Coverings b) Presenting parts
c)Relations d) Applied anatomy
4. Name the arteries supplying the thyroid gland.
5. Name the structures accompanying which can be
injured while ligating the arteries during
thyroidectomy.
Specific Learning Objectives
© Dr.N.Mugunthan

59. TAKE HOME MESSAGE
 Covered with true and false
capsule
 Moves with deglutition-
ligament of Berry
 Supplied by superior &
inferior thyroid arteries and
related with external &
recurrent laryngeal nerves.
 Development- median
thyroid element & lateral
thyroid rudiment
 Histology- thyroid follicles
and parafollicular cells
© Dr.N.Mugunthan

60. THYROID GLAND MOVES WITH DEGLUTITION
BECAUSE…..
Attachment of
pretracheal fascia (form
false capsule) from body
of hyoid bone to oblique
line of thyroid cartilage
Suspensory lig.of Berry
connects the lobe with
cricoid cartilage
© Dr.N.Mugunthan

61. 1. Superior thyroid artery
2. Inferior thyroid artery
3. Arteria thyroidea ima –
4. Numerous accessory
thyroid arteries ( from
tracheal & oesophageal
branches)
ARTERIAL SUPPLY
© Dr.N.Mugunthan

62. During thyroidectomy
Ligate the sup.thyroid
artery close to apex of
gland to avoid injury to
ext.laryngeal nerve
Ligate the inf.thyroid
artery away from base of
gland to avoid injury to
recurrent laryngeal nerve
STRUCTURES MAY GET INJURED WHILE LIGATING THE
ARTERIES
© Dr.N.Mugunthan

63. © Dr.N.Mugunthan