[003] Anat And Relations Of Thyroid

Question 1

Function of thyroid gland
(What system is it part of?)

Answer 1

Important gland of endocrine system

Secretes hormonal production directly into cell interstitium and blood stream

Question 2

Location of thyroid gland

Answer 2

Found directly beneath cricoid cartilage of larynx,
In midline of neck
Isthmus lies directly on trachea
Lateral lobes on lateral tracheal aspects

Question 3

General anatomy of thyroid

Answer 3

Isthmus, lateral lobe
A pyramidal lobe can be discerned sometimes

Question 4

What structures are posterior, medially-related to thyroid

Answer 4

Larynx, trachea
Oesophagus

Question 5

What structure is lateral to thyroid gland

Answer 5

Carotid sheath

Question 6

What structures are anteriorly related to thyroid

Answer 6

Pretracheal fascia
Infrahyoid muscles (Sternohyoid and Sternothyroid)

Question 7

What is the extent of movement of thyroid?

Answer 7

Covered by Pretracheal fascia and infrahyoid musculature, it
Moves up and down with larynx but cannot move above it (tethered)

Question 8

Parathyroid glands are part of which system?

Answer 8

Endocrine system

Question 9

Function of parathyroid glands

Answer 9

Secrete parathyroid hormone, which plays an important role in:
regulation of low blood calcium, influencing the amount of calcium in blood and within the bones

Question 10

Location of parathyroid glands

Answer 10

Four parathyroid glands : a superior and inferior pair

Parathyroid glands are embedded (mostly) on posterior aspect of thyroid gland but can vary considerably in position

Question 11

Blood and nerve supply of parathyroid gland

Answer 11

Share blood supply and nerve supply with surrounding thyroid gland

Question 12

Thyroid gland development: origins

Answer 12

Thyroid gland develops as an epithelial proliferation at the foramen caecum of developing tongue (embryonal week 4)

Question 13

Which pharyngeal pouches do parathyroid glands develop from?

Answer 13

Develops from 3rd (inferior pair) and 4th (superior pair) pharyngeal pouch respectively

Question 14

Thyroid and parathyroid development

Answer 14

By week 7, the thyroid will have migrated along the path of thyroglossal duct to its final position in relation to tracheal cartilages and cricoid cartilage

The inferior parathyroids will be pulled along with migration of thyroid and end below superior pair

Thyroglossal duct eventually regresses and obliterates (end of week 7)

Question 15

Arterial blood supply to thyroid and parathyroid

Answer 15

• superior thyroid arteries branch from external carotid
• inferior thyroid arteries arise from thyrocervical trunk

Question 16

What does the thyrocervical trunk supply

Answer 16

Shared supply to
- thyroid, parathyroid glands,
- scalene muscles
- parts of sternocleidomastoid and trapezius muscles

Question 17

Identify the arteries

Answer 17

Question 18

Variant of arterial blood supply to thyroid gland

Answer 18

Thyroid ima artery: supplies thyroid and trachea
In approximately 7-10% of population, an additional artery is found anterior to trachea, in midsagittal plane and at inferior aspect of thyroid isthmus

• originally an embryonic artery, arising from brachiocephalic trunk , or arch of aorta
• usually small or obliterated but can be substantial in variant to point where it is the main blood supply to thyroid

Question 19

Venous drainage of thyroid gland

Answer 19

To internal jugular and brachiocephalic veins
Via superior, middle and inferior thyroid veins which also form extensive anastomoses
(Inferior thyroid vein variable in size, can be just a single inferior thyroid vein lying in middle of trachea)

Question 20

Nerve supply to thyroid gland

Answer 20

Sympathetic trunk and branches of vagus nerve (superior laryngeal and recurrent laryngeal nerves)

Question 21

What do the recurrent laryngeal nerves run in close proximity to?

What is the significance of this during surgery?

Answer 21

Inferior thyroid arteries

During thyroid surgery, inferior thyroid artery needs to be lighted and sometimes this results in damage to one or both recurrent laryngeal nerves

Question 22

Lymphatic drainage of thyroid gland

Answer 22

Mostly to para-tracheal cervical and pre-tracheal lymph nodes
Lymphatics from gland usually pass to pre-laryngeal and tracheal nodes

May also pass directly into deep cervical nodes or into thoracic duct or right lymph duct

Question 23

What are lumps in the mid-sagittal plane in neck, caused by migratory development of thyroid

Answer 23

1. Thyroid cysts: persistent remnants of thyroglossal duct which fill with fluid and can produce fluctuate, pain-free midline swellings (soft to touch)
2. Lingual thyroid: ectopic thyroid tissue can be located along the route of thyroglossal duct

Question 24

What is an enlarged thyroid gland called

Answer 24

Goitre

Question 25

Presentation of goitre

Answer 25

Enlarged thyroid gland, producing a midsagittal swelling which does not rise above thyroid cartilage

Moves up and down with larynx, expands downwards to thoracic inlet

Question 26

What is the most common cause of goitre?

Answer 26

Iodine deficiency

Question 27

What are other causes of goitre?

Answer 27

• Congenital hypothyroidism,
• autoimmune diseases affecting thyroid,
• cancers of thyroid and
• disorders of hormonal organ system.

Question 28

Differentials of non-thyroid lumps of neck

Answer 28

Lymphadenopathy
Branchial cysts
Fistulae

Question 29

What is lymphadenopathy?

Answer 29

Enlarged lymph nodes, particularly with long-standing health issues
Eg chronic tonsillitis, tuberculosis, carcinoma etc

Question 30

Clinical notes when checking for lymphadenopathy
Hints: pain? How does it feel?

Answer 30

Usually solid, painful neck swellings
Can be Uni- or bilateral, always check for symmetry

Question 31

Branchial cysts and fistulae location and presentation

Answer 31

Located in lateral neck and usually present as fluctuant, pain-free one-sided swellings (differentiate from lymphadenopathy)

Question 32

How do Branchial cysts occur

Answer 32

When Branchial clefts (1-4) do not obliterate or when Branchial arches do not fuse properly (2,3) during embryonal development

Cysts develop along anterior border of sternocleidomastoid