7. The thyroid gland

Question 1

Where is the thyroid gland located?

Answer 1

in the neck - in front/around the lower larynx and upper trachea - isthmus extends from 2nd to 3rd rings of trachea

below thyroid cartilage (Adam’s apple)

Question 2

Is the thyroid gland usually visible/palpable?

Answer 2

No, only when enlarged - goitre

Question 3

Which nerves are at risk during thyroid surgery?

Answer 3

recurrent laryngeal and external branch of superior laryngeal - lie in close proximity to gland and must be avoided as supply the larynx and are involved in speech

Question 4

Describe the structure of the thyroid gland.

Answer 4

2 lobes joined by isthmus (“bow tie” shape and location)

Question 5

Describe the vascularisation of the thyroid gland.

Answer 5

highly vascularised - supplied by 3 arteries and drained by 3 veins: superior, middle and inferior thyroid arteries and veins

Question 6

Describe the embryological development of the thyroid gland.

Answer 6

1st endocrine gland to develop

1. appears at 3-4wks gestation as an epithelial proliferation in floor of pharynx at base (foramen cecum) of tongue. Over next several wks…
2. descends as thyroid diverticulum through thyroglossal duct and migrates downwards, passing in front of hyoid bone
3. during migration remains connected to tongue by thyroglossal duct which subsequently degenerates
4. detached thyroid then continues to final position over following 2 wks

Question 7

Describe the cellular composition of thyroid tissue.

Answer 7

• 2 major cell types in gland: follicular (epithelial) cells and parafollicular (C-cells)
• follicular cells arranged in spheres called thyroid follicles
• follicles separated by connective tissue containing the parafollicular cells
• follicles filled with colloid, a deposit of thyroglobulin

Question 8

What do thyroid follicular and parafollicular cells produce?

Answer 8

• follicular cells: thyroid hormone

- parafollicular cells: calcitonin (polypeptide hormone involved in calcium metabolism)

Question 9

What structures is the thyroid gland associated with?

Answer 9

associated but distinct from parathyroid glands (principal/chief cells produce parathyroid hormone)

Question 10

How is the thyroid gland attached to the trachea and larynx? What is the consequence of this?

Answer 10

pre-tracheal fascia

so thyroid moves upwards on swallowing

Question 11

How is the thyroid gland visualised?

Answer 11

Technetium-99m (can be injectible IV - rapid scan) used for isotope scanning of thyroid with a gamma camera (radiation exposure therefore low)

Question 12

What is a lingual thyroid?

Answer 12

ectopic thyroid (on tongue) resulting from lack of normal caudal migration of thyroid gland

Question 13

What is a thyroglossal duct cyst? How does it present?

Answer 13

• Thyroglossal duct normally disappears but remnants of thyroid epithelium may remain and form a thyroglossal duct cyst.
• Cyst usually near or within the body of the hyoid and forms a swelling in anterior part of neck, ALWAYS ON MIDLINE.
• Cyst MOVES UPWARDS on TONGUE PROTRUSION.