Fiser Chapter 22 THYROID Flashcards
Thyroid embryology
1st and 2nd pharyngeal ARCHES
Thyrotropin releasing factor (TRF)
Hypothalamus releases TRF -> acts on anterior pituitary -> TSH release -> acts on thyroid to release T3 and T4 (via increased cAMP)
T3 and T4 control TRF and TSH release by negative feedback loop
Thyroid blood supply
- Superior thyroid artery (1st branch off external carotid)
- Inferior thyroid artery (off thyrocervical trunk): supplies all parathyroids; so ligate close to thyroid to avoid injury to parathyroids
- Ima artery: occurs in 1%, arises from innominate or aorta and goes to isthmus
Thyroid veins
- Superior thyroid vein -> IJ vein
- Middle thyroid vein -> IJ vein
- Inferior thyroid vein -> innominate vein
Nerves around thyroid
- Superior laryngeal nerve: motor to cricothyroid, runs lateral to thyroid lobes, tracks close to superior thyroid artery (but variable); injury causes loss of projection and voice fatiguability
- Recurrent laryngeal nerve: motor to all larynx (except cricothyroid m), runs posterior to thyroid lobes in T-E groove, can track with inferior thyroid artery (but variable), L RLN loops around aorta, R RLN loops are innominate artery; injury causes hoarseness; bilateral injury can obstruct airway (need emergency tracheostomy); 2% has a Non-recurrent laryngeal nerve (more common on R); risk of injury is higher for non-recurrent laryngeal nerve during thyroid surgery
Ligament of Berry
Posterior medial suspensory ligament close to RLNs; need careful dissection
Thyroglobulin
Stores T3 and T4 in colloid
Plasma T4:T3 ratio is 15:1
T3 is more active form (tyrosine + iodine linked together by peroxidases; separated by deiodinases?)
Most T3 is produced in periphery from conversion of T4 to T3 via deiodinases
Most sensitive indicator of thyroid function
TSH
Thyroxine-binding globulin
Thyroid hormone transport: binds majority of T3 and T4 in circulation
Tubercles of Zuckerkandl
Most lateral, posterior extension of thyroid tissue
- Left behind with subtotal thyroidectomy because of proximity to RLNs
- Rotate medially to find RLNs
Calcitonin comes from what cells
Parafollicular C cells of thyroid
Thyroxine treatment
TSH levels should fall 50%
Osteoporosis is a long-term side effect
Post-thyroidectomy stridor
Open neck and remove hematoma emergently -> can result in airway compromise; can also be due to bilateral RLN injury -> would need emergent tracheostomy
Tachycardia, fever, numbness, irritability, vomiting, diarrhea, high-output cardiac failure
Thyroid storm (MCC of death is high-output cardiac failure)
- Most common after surgery in patient with undiagnosed Grave’s disease
- Can be precipitated by anxiety, excessive gland palpation, adrenergic stimulants
Tx of thyroid storm
Tx: Beta-blockers (first line), PTU, Lugol’s solution (potassium iodide -> Wolff-Chaikoff effect), cooling blankets, oxygen, glucose. Emergent thyroidectomy rarely indicated.
Wolff-Chaikoff effect
Give patient high dose of iodine (Lugol’s solution, potassium iodide), which inhibits TSH action on thyroid and inhibits organic coupling of iodide, resulting in less T3 and T4 release
Asymptomatic thyroid nodule: risk of malignancy
90% are benign
Asymptomatic thyroid nodule: management
- FNA (best initial test) and TFTs
Indeterminant thyroid FNA for asymptomatic thyroid nodule: next step?
-Radionuclide study
Hot versus cold nodule management
Hot nodule -> monitor if asymptomatic (if symptomatic, PTU and 131-I)
Cold nodule -> Lobectomy (more likely malignant)
Follicular cells on thyroid FNA, tx
Lobectomy (10% cancer risk)
Cyst fluid on thyroid FNA
Drain fluid
Lobectomy if bloody or recurs
Colloid tissue on thyroid FNA, tx
Thyroxine (colloid goiter, low chance of malignancy)
Lobectomy if enlarges
Normal thyroid tissue on FNA but TFTs elevated
Monitor if asymptomatic; PTU and 131-I if symptomatic
Likely solitary toxic nodule
Abnormal thyroid enlargement, dx and tx
Goiter: most identifiable cause iodine deficiency
Tx: Iodine replacement
If diffuse enlargement but no functional abnormality = nontoxic colloid goiter
-Unusual to require surgery unless causing airway compression or suspicious nodule -> subtotal or total thyroidectomy (subtotal has reduced risk of RLN injury)
Abnormal thyroid enlargement, dx and tx
Goiter: most identifiable cause iodine deficiency
Tx: Iodine replacement
If diffuse enlargement but no functional abnormality = nontoxic colloid goiter
-Unusual to require surgery unless causing airway compression or suspicious nodule -> subtotal or total thyroidectomy (subtotal has reduced risk of RLN injury)
Substernal goiter
Usually secondary (vessels originate from superior and inferior thyroid artery)
Primary substernal goiter rare (vessels originate from innominate artery)
?
Mediastinal thyroid tissue
Most likely from acquired disease with inferior extensions of normally placed gland (eg substernal goiter)
Abnormalities of thyroid descent
- Pyramidal lobe: extends from isthmus toward thymus
- Lingual thyroid: thyroid tissue persisting in foramen cecum at base of tongue
- Thyroglossal duct cyst
Lingual thyroid presentation and tx
Dysphagia, dyspnea, dysphonia
2% malignancy risk
Tx:
- Thyroxine suppression
- Abolish with 131-I
- Resect if worried about CA or does not shrink after medical therapy
- is the only thyroid tissue in 70% who have it
Thyroglossal duct cyst presentation and tx
- Moves upward with swallowing
- Susceptible to infection and may be premalignant
Tx: Sistrunk procedure (resect cyst and take midportion or all of hyoid bone along with it)
Hyperthyroidism treatment
PTU (propylthiouracil)
Methimazole
Radioactive iodine (131-I)
Thyroidectomy
PTU (propylthiouracil)
Inhibits peroxidases and prevents iodine-tyrosine coupling
Safe for PREGNANCY, good for young patients, small goiters, mild T3 and T4 elevation
Side effects: aplastic anemia, agranulocytosis
Methimazole
Inhibits peroxidases and prevents iodine-tyrosine coupling
Good for youn
