surgical anatomy and significant surgical notes on thyroid gland

1. Embryology and Anatomy of
THYROID GLAND
Supervised by : Dr. Sarmad Hiwa
Prepared by : Zryan Salar

2. Thyroid Embryology
• The Thyroid gland is the first of the body's endocrine
glands to develop, at 24th Day of gestation.
• The thyroid originates from two main structures:
1-The primitive pharynx : median thyroid, which forms
the bulk of the gland .
2-Neural crest. The rudimentary lateral thyroid.
This occurs under the influence of fibroblast growth factor

3. • The thyroid gland forms from endodermal epithelial
cells on the median surface of the developing
pharyngeal floor.
• The site of this development lies between 2 key
structures, the tuberculum impar and the copula,
and is known as the foramen cecum

4. • The initial thyroid precursor, the thyroid primordium, starts as
a simple midline thickening and develops to form the thyroid
diverticulum.
• Originates from between the 1st and 2nd pouches
• This structure is initially hollow, later solidifies and becomes
bilobed.
• The stem usually has a lumen, the Thyroglossal duct, that
does not descend into the lateral lobes.
• The 2 lobes are located on either side of the midline and are
connected via an isthmus

5. Descent of the Thyroid Gland
• The initial descent of the thyroid gland follows the
primitive heart and occurs anterior to the pharyngeal
gut. At this point, the thyroid is still connected to the
tongue via the thyroglossal duct
• in some individuals, remnants of this duct may still
persist .

6. • Descent of the thyroid gland
carries it anterior (or ventral)
to the hyoid bone and, anterior
to the laryngeal cartilages.
• As the thyroid gland
descends, it forms its mature
shape, with a median isthmus
connecting the two lateral
lobes.
• The thyroid completes its
descent in the 7th gestational
week, coming to rest in its final
location immediately anterior
to the trachea

7. • Defective embryogenesis of
the thyroid gland as it
descends to its target
location can result in ectopic
thyroid tissue

8. Clinical Correlations
• If the thyroglossal duct does not atrophy, then
the remnant can manifest clinically as a
thyroglossal duct cyst (TDC)

9. Clinical Correlations
• Most cases of ectopic thyroid are detected in
early childhood and may be associated with
hypothyroidism .
• Accessory thyroid tissue can also occur, arising
from remnants of the thyroglossal duct.
• While the accessory thyroid tissue may be
functional, it is generally insufficient for
normal function if the main thyroid gland is
entirely removed.

10. Anatomy of Thyroid gland
• The thyroid is a highly vascular, brownish-red gland located
anteriorly in the lower neck .
• Extending from the level of the C5 to T1 vertebrae.
• The gland varies from an H to a U shape and is formed by 2
elongated lateral lobes with superior and inferior poles
connected by a median isthmus.
• Overlying the 2nd to 4th tracheal rings.
• Each lobe is 50-60 mm long .
• It averages 25-30 g in adults .

11. Arterial supply of Thyroid gland
• from the Superior and Inferior thyroid arteries
and, occasionally, from the thyroidea ima.
Ant.
Post.

12. Venous Drainage
Three pairs of veins:
• The superior thyroid vein to
internal jugular vein .
• The middle thyroid vein to the
internal jugular vein .
• The inferior thyroid veins to
brachiocephalic veins . ( V )

13. Lymphatic drainage of the thyroid gland
lymphatic drainage to the periglandular nodes;to the :
1-Prelaryngeal nodes
2-Pretracheal nodes
3-Paratracheal nodes
to Cervical and then to Mediastinal lymph nodes

14. Innervation of the thyroid
• Principal innervation of the thyroid
gland derives from the autonomic nervous
system.
• Parasympathetic fibers come from the vagus
nerves .
• Sympathetic fibers are distributed from the
superior, middle, and inferior ganglia of the
sympathetic trunk

15. Surgical Significance Anatomy
1. Pyramidal lobe (PL)
2. Tubercle of Zuckerkandl (TZ)
3. Ligament of Berry (LB)
4. External branch of superior
laryngeal nerve (EBSLN)
5. Inferior thyroid artery (ITA)
6. Recurrent laryngeal nerve (RLN)
7. Parathyroid glands (PT)
8. Pretracheal fascia (PTF)
9. Pretracheal plane (PTP)
10.Thyrocarotid space (TCS)
11.Linea alba of neck (LAN)

16. Pyramidal lobe
• The distal end of thyroglossal tract persists as PL in up to 44–61 % of cases
The clinical significance of PL lies in its non-resection during total
thyroidectomy, which could lead to the following:
1. Recurrence of hyperthyroidism due to compensatory hyperplasia in toxic
goiters
2. Recurrence of goiter in nodular goiters
3. Recurrent malignancy in differentiated thyroid cancer due to multifocality
4. Recurrent thyroglossal fistula

17. • It is the condensed
thyroid parenchyma
located in the cricothyroid
junction
• TZ is the site for maximum
density of C cells, making
its resection mandatory in
total thyroidectomy for
medullary thyroid cancer
Tubercle of Zuckerkandl TZ

18. Ligament of Berry
• Condensation of PTF along with an entrapped layer of
thyroid parenchyma on the posterolateral aspect of the
thyroid gland.
• At surgery, an excessive medial rotation of thyroid gland
leads to kinking of RLN due to its close proximity and
entrapped location within the posterior fibers of LB.
• Another surgical significance is the presence of perforating
laryngeal blood vessels parallel to LB, which leads to
bleeding if LB is not ligated.
• LB also marks the most common site for
airway invasion in high risk and
poorly differentiated thyroid cancer

19. External branch of superior laryngeal nerve
• It is purely a motor branch of vagus nerve , supplies the
cricothyroid muscle which primarily controls the quality and pitch
of voice.
• Careful and mandatory search for it prevents injury .
• palsy leads to significant morbidity especially in teachers and
professional singers .

20. Inferior thyroid artery
• ITA is the second major arterial supply of thyroid
gland and the main vascular source of parathyroid .
• Ligation of terminal branches of ITA, close to the
thyroid capsule and away from RLN, is another
yardstick for an expert thyroid surgery.
• Ligation of the trunk of ITA may affect the vascular
supply of parathyroid glands

21. Recurrent laryngeal nerve
• RLN supplies all the intrinsic laryngeal muscles except the
cricothyroid. It also provides sensory supply to infraglottic
mucosa.
• RLN palsy can lead to hoarseness of voice, dysphagia, ineffective
cough, and respiratory difficulty.
• Prevention of RLN injury is another skill test for thyroid surgeons.
• Capsular dissection of the thyroid and delineation of anatomical
landmarks such as tracheoesophageal groove, ITA, TZ, LB, and
inferior constrictor muscle are few basic surgical principles
forming essential components of any approach for identification
and preservation of RLN

22. RLN

23. Parathyroid glands
• Preservation of
vascularized and functional
PT glands is another
challenge in thyroid surgery
.
• Injuries avoided by minimal
handling of PT and ligation
of individual blood vessels
close to the thyroid gland .

24. Pretracheal fascia
• It is one of the four well-defined layers of the deep cervical
fascia .
• forms the pseudocapsule of the thyroid gland outside its true
capsule.
• Its surgical significance lies in dissecting between the PTF and
the true capsule of the thyroid gland for thyroidectomy

25. Pretracheal plane
• This is a surgical plane located in between the posterior
surface of thyroid gland and tracheal perichondrium .
• Multiple perforating blood vessels traverse this space
between the thyroid gland and trachea.
• necessitates sharp dissection in this plane

26. Thyrocarotid space
• This is a lateral space in the visceral compartment of the
neck’s deep cervical fascia and sternocleidomastoid muscle
(SCM) between common carotid artery laterally, thyroid gland
medially, and prevertebral fascia posteriorly .
• The surgical importance lies in its provision of an alternative
route to the traditional midline approach for goiter.
• This lateral approach is especially beneficial in reoperative
cases, malignant and large goiters.

28. Linea alba of neck
This is the midline interface between bilateral strap
muscles formed by thickened deep cervical fascia,
anterior to the thyroid gland .

29. THANKS