Thyroid/Parathyroid

Question 1

Embryological origin of thyroid gland and descent?

Answer 1

Foramen cecum (midline diverticulum at the floor of the pharynx) Descends down the neck through the thyroglossal duct

Question 2

Ectopic thyroid tissue locations

Answer 2

Anterior mediastinum Central neck Lateral neck - not ectopic, just well differentiated thyroid cancer

Question 3

Ligament of Berry

Answer 3

Posteromedial suspensory ligament that is attached to upper 2-3 tracheal rings and cricoid cartilage RLN usually just lateral to ligament, in 25% of cases nerve is surrounded by ligament before entrance into larynx

Question 4

Arterial supply of thyroid

Answer 4

2 superior arteries: -superior thyroid artery: 1st anterior branch of ECA -runs with external branch of superior laryngeal nerve 2 inferior arteries: -inferior thyroid artery: from thyrocervical trunk -supplies blood to superior/inferior parathyroid glands -runs with RLN

Question 5

Right RLN path

Answer 5

arises from vagus at crossing with subclavian vein, usually ascends 1-2 cm lateral to tracheoesophageal groove

Question 6

Left RLN path

Answer 6

Arises from behind aortic arch, typically arises in tracheoesophageal groove

Question 7

Superior laryngeal nerve path

Answer 7

Arises from vagus, desceds along ICA

• internal branch: sensory, enters larynx via thyrohyoid membrane
• external branch: descends just medial to superior thyroid artery and enters cricothyroid muscle

Question 8

1st step in work up of a thryoid nodule?

Answer 8

H&P

FNA

Question 9

Total thryoidectomy vs near-total vs subtotal thyroidectomy

Answer 9

Total: all visible thyroid tissue is removed bilaterally

Near-total: all visible thyroid tissue is removed on one side and a small rim is left on the other side

Subtotal: small rim of thyroid tissue is left bilaterally to ensure parathyroid viability

Question 10

MC thyroid cancer

Answer 10

Papillary thyroid cancer

Question 11

Psammoma bodies on histology

Answer 11

Papillary thyroid cancer

Question 12

Tx of papillary thyroid cancer

Answer 12

1 cm lesion: lobectomy and isthmectomy

>2 cm: total or near total thyroidectomy

Palpable adenopathy: modified radical neck dissection and total thyroidectomy

Radioiodine is used as an adjunctive therapy

Question 13

Embryology of parathyroid glands

Answer 13

Superior parathyroids arise from 4th pharyngeal pouch

Inferior parathyroids arise from 3rd pharyngeal pouch

Question 14

Primary hyperparathyroidism lab findings

Answer 14

High Ca

High PTH

High urinary Ca

Hyperchloremic metabolic acidosis

Question 15

Parafollicular C cells derived from

Answer 15

Neural crest

Produce calcitonin

Question 16

Drugs that block peripheral conversion of T4 to T3

Answer 16

PTU

Propanolol

Prednisone (steroids)

T3 is 3x as active as T4

Question 17

Follicular thyroid cancer spread vs PTC

Answer 17

Spreads hematogenously

PTC - lymphatic spread

Question 18

Medullary thyroid cancer histologic finding

Answer 18

Amyloid stroma

Question 19

Superior laryngeal branch injury

Answer 19

External branch - motor to cricothyroid muscle, injury causes loss of projection and high pitch

Question 20

What is the Wolff-Chaikoff-White effect?

Answer 20

Iodine binding by thyroid and production of T3 and T4 are inhibited as plasma iodine levels accumulate beyond a critical level

Iodine is the most effective means to rapidly decrease thyroid hormone levels (Lugols)