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*
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
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?
22.
23.
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?
25.
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
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*
31.
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
33.
34.
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)
36.
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
38.
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)
44.
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
47.
48.
49.
50.
51.
52.
53. In agenisis of ishthmus and lobes presence of ectopic thyroid tissue must be
looked for