THYROID GLAND , ANATOMY , VARIATIONS, DEVELOPMENT RELATIONS

2. ANATOMY OF THYROID GLAND
AHAMMED KABEER M A
55TH BATCH
GOV MED COLLEGE
CALICUT

3. INTRODUCTION
DEVELOPMENT
GROSS ANATOMY
BLOOD SUPPLY
NERVE SUPPLY
LYMPHATIC DRAINAGE
HISTOLOGY
SURFACE ANATOMY
APPLIED ANATOMY

4. • Largest endocrine gland
• Thyroid hormones (T3 , T4 )- BMR
• Thyrocalcitonin – antagonize PTH
(i.e decrease serum Ca)
• Highly vascular*

5. DEVELOPMENT OF THYROID GLAND
• Median endodermal thyroid diverticulum
• Thyroglossal duct
• Tuberculum impar
• Foramen caecum
• Lateral thyroid (4th pouch n ultimobranchial body) – parafollicular
cells

7. SITUATION
C5
T1 / 4th or 5th
tracheal ring
2nd
4th
Tracheal rings

8. DIMENSIONS AND WEIGHT
• Butterfly/H shaped
• Lobes 5*3*2cm
• Isthmus 1.2*1.2cm
• Weight 25g
• Larger in females
• Enlarges in pregnancy & menstrution

9. CAPSULES
• True capsule (fibrous) – condensation of CT of gland
• Septae & lobules
• Arteries and plexus of veins deep to it
• False capsule – pretracheal fascia
• Moves during deglutition and speech
• Suspensory ligament of Berry*

10. Deep cervical fascia

11. RELATIONSs
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

12. • Apex is sandwitched b/w inf constrictor and sternothyroid I.e upward
extension is restricted

13. • Lateral surface – convex,
• Covered with sternohyoid, SCM, superior belly of
omohyoid, sternothyroid

14. Deep cervical fascia

16. • Medial surface- 2 tubes(larynx-trachea) and (pharynx-oesophagus)
- 2 muscles cricothyroid, inferior constrictor
- 2 nerves external and recurrent laryngeal N
• PL surface – carotid sheath

17. • Ant border – anterior branch of STA

18. • P border - ITA
- anastomosis b/w STA & ITA
- parathyroid glands
- thoracic duct on left

19. 2. Isthmus
• 2 surfaces A & P
• 2 borders Sup & Inf
• A surface – skin & fascia
- anterior jugular veins
- R & L sternohyoid & sternothyroid
• P surface- 2nd – 4th tracheal rings
• Sup border – anastomosis b/w R&L STA
• Inf border - ITV leave

20. Pyramidal lobe
• Extend superiorly from isthmus/left lobe
• Attached to body of hyoid bone by fibromuscular band
• Levator glandulae thyroidae( LGT)
• U/L or B/L
• LGT represent detached part of infrahyoid muscles
• May be innervated by ansa cervicalis
• Remnant of thyroglossal duct

21. BLOOD SUPPLY – Arterial supply
1. Superior thyroid artery (STA)
• 1st ant br of ECA
• External laryngeal N *
• Ligature *
• Pierce pretracheal fascia at apex
• Divide into A & P branches
• A branch- ?
• P branch?

24. 2. Inferior thyroid artery (ITA)
• Largest branch of thyrocervical trunk (SCA)
• Pass behind carotid sheath, MCG and in front of vertebral A
• Terminate near lower pole
• Recurrent laryngeal N*
• Ligation*
• Ascending br*?
• Glandular br?

26. 3. Thyroidea ima artery*( lowest thyroid artery) 3%
• from arch of aorta/brachiocephalic trunk/right common carotid/right
subclavian/ internal thoracic A
• Enter lower border of isthmus
• Tracheostomy*
4. Accessory thyroid arteries

28. VENOUS DRAINAGE
1. Superior thyroid vein (STV)
• Accompany STA
• Drain to IJV/ facial v

29. 2. Middle thyroid vein
• Very short
• From middle of lobe
• Drain to IJV

30. 3.Inferior thyroid vein*
• Plexus on trachea
• Drain to left brachiocephalic vein
• R – passes ant to innominate a  R BCV or ant trachea  L BCV
• L – drainage  L BCV
• **occ – both inf veins form a common trunk “thyroid ima vein” 
empties into L BCV
• Thyroid vein of Kocher* emerge from lower pole drain to IJV
profuse bleeding
4. kocher’s thyroid vein*

32. LYMPHATIC DRAINAGE
• 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

35. INNERVATION
• Vasoconstrictor sympathetic innervation
• Mainly from MCG
• Partly from SCG and ICG
• Cardiac and laryngeal branches of vagus(parasympathetic)
• Enter along wuth blood vessels
• Never secretomotor (secretion regulated by TSH)

37. HISTOLOGY
• Septae from fibrous capsule
• Lobules
• Follicles filled with colloid
• Follicular cells- T3 ,T4 ( level of activity)
• Parafollicular cells( Clear cells, pale cells)- thyrocalcitonin
(ultimobranchial body), an APUD cell
• Colloid – iodothyroglobulin

39. SURFACE ANATOMY
• Anterior triangles in the lower neck on either side of the air way and
digestive tract inferior to the position of the oblique line of the
thyroid cartilage .
• sternothyroid muscles- oblique line of thyroid cartilage ,prevent the
lobes from moving upwards
• Palpated by finding the thyroid prominence and arch of the cricoid
cartilage and then feeling posterolateral to the larynx.
• Isthmus crosses anterior to the upper end of the trachea and can be
easily palpated in the midline inferior to the arch of the cricoid.
• Presence of isthmus makes palpating the tracheal cartilages difficult
and difficult tracheostomy.

40. • Isthmus marked by –
• Lobes extend – apex to middle of thyroid crtilage
- base to clavicle
- laterally overlapped by ant border of SCM
Arch of cricoid
1.2cm
1.2cm
1.2cm

41. APPLIED ANATOMY
• Presence of thyroidae ima A- chance of profuse bleeding
procedures in neck below isthmus
• Thyroglossal duct cysts – remnants of thyroglossal ducts at any point
in the way of descent,(midline near hyoid)
• Pyramidal lobe and presence of levator glandulae thyroidae
• Ectopic thyroid glands – lingual/higher placed
• Accessory thyroid glands – in thymus/ on thyrohyoid muscle
• Non neoplastic, noninflammatory enlargement – goiter

42. • pressure symptoms and nerve involvments are common in goiter
and carcinoma
• Compression of trachea, carotid sheath, and venous engorgement

43. • Endemic goiter - I2 deficient soil/water
• Subtotal thyroidectomy often preferred in hyperthyroidism –
-to preserve external and recurrent laryngeal N
- to spare parathyroid glands
- to prevent post operative myxoedema
• Injury to recurrent laryngeal N – horsness of sound
-temporary aphonia/ dysphonation
- laryngeal spasm
• Recurrent laryngeal N- supply all laryngeal muscles except *cricothyroid
• Nonrecurrent laryngeal N*
• Injury to external laryngeal N – monotonous voice(paralysis of
cricothyroid)
• Inadvert removal of parathyroid gland – tetany (fatal)

45. - relationship between RLN and ITA highly variable
Examples:
• Deep to ITA (40%)
• superficial (20%)
• b/w branches of the artery (35%)

46. Anomalies of development
• Anomalies of shape
• Anomalies of position
• Ectopic thyroid glands
• Remnants of thyroglossal duct

53. In agenisis of ishthmus and lobes presence of ectopic thyroid tissue must be
looked for

55. Thyroglossal fistula
Thyroglossal cyst

56. Thyroid Neoplasm
Benign Malignant
PrimaryFollicular
Papillary
Follicular
Cells
Parafollicular
Cells
Lymphoid
Cells
LymphomaMedullary
Differentiated Undifferentiated
AnaplasticFollicular
Papillary
Hurthle Cell
Secondary