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Surgery M4 part 1 > Thyroid Gland anatomy & investigations > Flashcards

Thyroid Gland anatomy & investigations Flashcards

1
Q

What does the thyroid gland develop from?

A

the endodermal diverticulum in the middle of the primitive pharynx (FORAMEN CAECUM of tongue)

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2
Q

Describe the development of the thyroid gland?

A

the diverticulum elongates forming the thyroglossal duct —> thyroglossal duct descends caudally in front of the primitive pharynx and in front of hyoid bone —> duct bifurcates at the level of the thyroid cartilage to form lobes and isthmus and pyramidal lobe

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3
Q

What is responsible for the development of the most lateral parts of the lateral lobes of thyroid gland?

A

from the 4th pharyngeal arch ULTIMOBRANCHIAL BODY

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4
Q

What thyroid cells are derived from the neural crest? and what is their function?

A

parafollicular C cells

secretion of calcitonin

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5
Q

Where is the thyroid located?

A

lower part of the neck in the muscular triangle infront of sternomastoid muscle

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6
Q

where are the right and left lateral lobes located?

A

extend from the oblique line of the thyroid cartilage to the 6th tracheal ring

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7
Q

where is the isthmus located?

A

connects the 2 lateral lobes in midline extending from 2nd to 4th tracheal rings

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8
Q

What are the medial relations of the thyroid glands?

A
  • upper part: larynx & pharynx with superior laryngeal nerve in between
  • lower part: trachea & esophagus with recurrent laryngeal nerve
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9
Q

What are the posterolateral relations of the thyroid?

A

Carotid sheath & its contents

  • artery CAROTID ARTERY
  • vein INTERNAL JUGULAR VEIN
  • 2 nerves CERVICAL 1 SYMPATHETIC CHAIN & VAGUS NERVE

Superior & inferior parathyroid glands & muscles

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10
Q

What is the superficial relation of the thyroid gland?

A 
skin
platysma 
sternomastoid 
STRAP MUSCLES 
- sternohyoid 
- sternothyroid 
- omohyoid
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11
Q

What is the recurrent laryngeal related to?

A

Berry’s ligament: condensation of pretracheal fascia forming the ligament

during surgery be careful not to injure the recurrent laryngeal nerve next to it

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12
Q

What muscles does the superior laryngeal nerve supply?

A

it gives the external laryngeal branch which supplies the cricothyroid muscle responsible for HIGH PITCH

accompanies superior thyroid artery

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13
Q

the superior laryngeal nerve originates from which nerve?

A

Vagus nerve

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14
Q

The internal laryngeal nerve supplies?

A

mucous membranes above vocal cords

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15
Q

What does the recurrent laryngeal nerve supply?

A

motor: all internal laryngeal muscles except cricothyroid
sensory: mucous membranes below vocal cords

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16
Q

What are the coverings of the thyroid gland?

A
  • true capsule surrounding the thyroid gland itself

- false capsule surrounding the whole thyroid formed from PRETRACHEAL FASCIA is attached to the hyoid bone superiorly

17
Q

What is the blood supply of the thyroid artery?

A
  • SUPERIOR THYROID ARTERY
    (accompanying the external laryngeal nerve)
    FROM external carotid artery
  • INFERIOR THYROID ARTERY
    (accompanying recurrent laryngeal nerve)
    FROM thyrocervical trunk of the 1st part of subclavian
  • THYROID IMA branch of aorta or brachiocephalic
  • TRACHEAL AND OESOPHAGEAL BRANCHES
    to retain thyroid gland after thyroidectomy
18
Q

What is the venous drainage of the thyroid gland?

A

SUPERIOR THYROID VEIN -> drains into the internal jugular
MIDDLE THYROID VEIN -> short & drain into internal jugular
INFERIOR THYROID VEIN -> tracheal & esophageal branches

19
Q

What are the 2 secretory cells of the thyroid gland?

A
  • follicular cells: T3 & T4

- Parafollicular cells (C cells): calcitonin

20
Q

What are the lymph nodes that drain the thyroid?

A
  • prelaryngeal
  • pretracheal
  • paratracheal
    they all drain into superior & inferior deep cervical nodes
21
Q

What are the mechanisms of thyroid hormone synthesis??

A

1- IODINE TRAPPING: inorganic iodide is picked up by thyroid under the influence of TSH
2- OXIDATION: perioxidaze turns it to organic iodine
3- BINDING: organic iodine with tyrosine forming iodothyronins (MIT, DIT)
4- COUPLING: of MIT & DIT forming T3 & T4
5- RELEASE: by splitting thyroglobulin by protease
T3 & T4 bind to albumin & globulin but a small portion is free and physiologically active

22
Q

What are the functions of thyroxin?

A
  • stimulate O2 consumption (energy production)
  • stimulate glucose utilization by tissue
  • enhance protein catabolism
  • decrease serum cholesterol level
  • sensitize heart & CNS to catecholamines
  • stimulate physical mental and sexual growth in children
23
Q

Whats the function of calcitonin?

A

lowering the serum calcium level (antagonist for parathormone)

24
Q

What changes will occur in the hormone levels incase of hyperthyroidism & hypothyroidism?

A

Hyperthyroidism Hypothyroidism
T3 increase decrease
T4 increase decrease
TSH decrease increase

25
Q

What is the most important investigation for follow up?

A

THYROID FUNCTION TEST (TSH)
- free is more sensitive than total
- can differentiate between high normal and abnormally high thyroid hormones
from 4000 - 11000 NORMAL

26
Q

What condition is caused due to high T3 & normal T4?

A

T3 thyrotoxicosis

27
Q

What investigation is used to diagnose Grave’s disease or autoimmune thyroiditis?

A

AUTOANTIBODY TITERS

28
Q

What are the types of autoantibodies?

A
  • LATS (trab)
    TSH receptor antibody: bind to TSH receptors and increase stimulation causing GRAVES
  • Anti PO, antimitochondrial, antithyroglobulin
    inhibitors of thyroid hormone formation cause HASHIMOTO
29
Q

What is the most important method of investigation to differentiate between a toxic nodule and a solitary nodule of toxic nodular goiter?

A

isotope scan

  • hot nodule takes up isotope but surroundings don’t
  • warm nodules takes up isotope and surroundings do
  • cold nodules do not take up isotope
30
Q

What is the first line method of radiological investigation in case of suspected thyroid disease?

A

ultrasonography

  • detect enlargement of thyroid gland
  • comment on any nodules or cysts
  • guide FNAC
  • asses malignant lymphadenopathy
31
Q

How to differentiate between a benign or malignant cyst in the thyroid?

A

BENIGN MALIGNANT
- smooth - rough
- regular - irregular
- clear content - turbid content
- serous fluid - bloody fluid
- no residual mass - residual mass after aspiration
after aspiration
- no or slow recollection - rapid recollection
- no malignant cells - malignant cells

32
Q

What are the important TIRADS scores?

A

TR 1 = no FNA

TR 2 = no FNA

TR 3 = monitor if > or = to 1.5cm
= FNA if > or = to 2.5cm

TR 4 = follow if > or = to 1cm
= FNA if > or = to 1.5cm

TR 5 = follow if > or = 0.5cm
= FNA if > or = to 1cm

33
Q

What is the investigation of choice in discrete thyroid swellings?

A

FNAC

  • can diagnose colloid nodules, thyroiditis, papillary carcinoma. medullary carcinoma, anaplastic carcinoma & lymphoma
  • CAN’T distinguish between follicular adenoma or carcinoma
34
Q

When is indirect laryngoscopy used?

A

to assess vocal cords before surgery

35
Q

What method of investigation is best for assessing retrosternal & recurrent swellings?

A

CT & MRI

36
Q

What is the importance of neck X-ray?

A

demonstrates

  • tracheal deviation
  • compressions
  • retrosternal extension
  • ring or rim calcification
37
Q

Which method of investigation is malignancy specific?

A

PET scan

localizes disease that doesn’t take up radioiodine

38
Q

What is the most confirmatory line of investigation in a solitary thyroid nodule?

A

FNABC

39
Q

during thyroidectomy, surgeon should consider special care during ligation of superior thyroid artery as he may affect?

A

cricothyroid muscle supplied by the external laryngeal nerve

Surgery M4 part 1 (47 decks)

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