Thyroid gland (dave's notes)

Question 1

Describe the shape and location of the thyroid gland

Answer 1

Two symmetrical lobes united in front of the 2nd, 3rd, and 4th tracheal rings by a glandular isthmus

Question 2

What is the shape of the lateral lobes of the thyroid?

Answer 2

Pear or triangular in shape with a narrow upper pole and a broad lower pole

Question 3

What is the shape of the lateral lobe of the thyroid in cross section? What surfaces does it have?

Answer 3

Triangular, with lateral, medial and posterior surfaces

Question 4

What covers the lateral surface of the lateral lobe of the thyroid?

Answer 4

Sternothyroid and sternohyoid

Question 5

What is in contact with the medial surface of the lateral lobe of the thyroid?

Answer 5

The lateral side of the larynx and upper trachea

Question 6

How far inferior may the lower pole of the thyroid extend?

Answer 6

The 6th tracheal ring.

Question 7

What are the medial muscular relations of the thyroid?

Answer 7

Cricothyroid and inferior constrictor muscles

Question 8

What nerve approaches the thyroid from above? What nerve from below?

Answer 8

External laryngeal nerves approach from above

Recurrent laryngeal nerve from below

Question 9

What does the posterior surface overlap? What may happen in pathological enlargement here?

Answer 9

The posterior surface overlaps the medial part of the carotid sheath and can extend past the internal jugular vein in enlargement

Question 10

Where are the parathyroid glands usually found?

Answer 10

In contact with the posterior surface of the lateral lobes of the thyroid

Question 11

Via what route to the recurrent laryngeal nerves approach the thyroid? How does the left differ from the right RLN?

Answer 11

The recurrent laryngeal nerves approach the medial surface of the gland from below, just in front of the trachea-oesophageal groove. The left is more likely to lie behind the inferior thyroid artery. On the right there is an equal chance.

Question 12

What is the recurrent laryngeal nerve always found behind?

Answer 12

The pretracheal fascia and behind the cricothyroid joint; here it passes upwards under inferior constrictor

Question 13

What may happen to the recurrent laryngeal nerve at the upper border of the isthmus?

Answer 13

It may divide into two. The anterior branch will always be motor.

Question 14

How does the external laryngeal nerve approach the thyroid?

Answer 14

It runs down to supply cricothyroid behind the superior thyroid artery

Question 15

Describe the thyroid isthmus

Answer 15

The thyroid isthmus joins the anterior surfaces of the left and right thyroid lobes and is firmly adherent to the 2nd, 3rd, and 4th tracheal rings.

Question 16

What runs across the thyroid isthmus?

Answer 16

An arterial anastomosis.

Question 17

Where may a pyramidal lobe be found? What does this represent?

Answer 17

A pyramidal lobe may be found projecting forwards on the left representing the caudal end of the thyroglossal duct.

Question 18

What other developmental remnant may be found?

Answer 18

An accessory remnant may also be found

Question 19

What is the arterial supply to the thyroid?

Answer 19

Superior thyroid
Inferior thyroid
Thyroidea ima artery

Question 20

From what does the superior thyroid arise? What branches does it give off first?

Answer 20

The first branch of the anterior aspect of the external carotid.
Gives off SCM and superior laryngeal branches before piercing the pretracheal fascia to reach the summit of the upper pole.

Question 21

What is found immediately behind the superior thyroid artery?

Answer 21

The external laryngeal nerve. The artery is divided right at the pole.

Question 22

From what does the inferior thyroid artery arise? What branches does it give off first?

Answer 22

The inferior thyroid artery arises from the thyrocervical trunk. It arches upwards behind the lower pole to divide outside the pretracheal fascia into 4-5 branches that pierce separately.
Gives of oesophageal and inferior laryngeal branches first.
In thyroidectomies is ligated well lateral.

Question 23

Where is the thyroidea ima artery found? From which arteries may it originate?

Answer 23

The thyroidea ima artery enters the lower part of the isthmus in 3% of individuals. It can arise from the brachiocephalic trunk, the right common carotid, or the aortic arch.

Question 24

Describe the venous drainage of the thyroid

Answer 24

Venous return from the upper pole follows the superior thyroid artery (superior thyroid vein) to the internal jugular vein or the FV (??).
The middle thyroid vein passes from the middle directly to the IJV.
Inferior thyroid veins form a plexus which drains primarily into the left brachiocephalic vein.

Question 25

Where does thyroid lymph drain to?

Answer 25

Lymph drainage follows the arteries.

The upper pole drains to the anterosuperior group, and the lower pole to the postero-inferior group.

Question 26

Describe the nerve supply to the thyroid

Answer 26

The bulk of sympathetic supply is from the middle cervical ganglion, fibres of which enter on the inferior thyroid artery. A few vagal filaments also exist.

Question 27

What percentage of cells are parafollicular? What do they secrete?

Answer 27

2%, Calcitonin

Question 28

Describe the histological structure of the thyroid

Answer 28

The thyroid has a mass of rounded follicles full of colloid (iodine containing product of epithelial cells). Colloid is iodinated within the cells, stored outside, then reabsorbed for transport

Question 29

Summarise the development of the thyroid

Answer 29

The thyroid develops as a proliferation of cells from the caudal end of the thyroiglossal duct. Parafollicular calcitonin cells come from the 5th pharyngeal pouch, but no other part does.