From the 1st and 2nd pharyngeal arches (not from pouches)

  Thyrotropin-releasing factor (TRF) – released from the hypothalamus; acts on the anterior pituitary gland and causes release of TSH

  Thyroid-stimulating hormone (TSH) – released from the anterior pituitary gland; acts on the thyroid gland to release T3 and T4 (through a mechanism that involves ↑ cAMP)

  TRF and TSH release are controlled by T3 and T4 through a negative feedback loop

  Superior thyroid artery – 1st branch off external carotid artery

  Inferior thyroid artery – off thyrocervical trunk; supplies both the inferior and superior parathyroids

•  Ligate close to thyroid to avoid injury to parathyroid glands with thyroidectomy

  Ima artery – occurs in 1%, arises from the innominate or aorta and goes to the isthmus

  Superior and middle thyroid veins – drain into internal jugular vein

  Inferior thyroid vein – drains into innominate vein

  Superior laryngeal nerve

•  Motor to cricothyroid muscle

•  Runs lateral to thyroid lobes

•  Tracks close to superior thyroid artery but is variable

Injury results in loss of projection and easy voice fatigability (opera singers)

  Recurrent laryngeal nerves (RLNs)

•  Motor to all of larynx except cricothyroid muscle

Run posterior to thyroid lobes in the tracheoesophageal groove

•  Can track with inferior thyroid artery but are variable

•  Left RLN loops around aorta; right RLN loops around innominate artery

•  Injury results in hoarseness; bilateral injury can obstruct airway → need emergency tracheostomy

•  Non-recurrent laryngeal nerve – in 2%; more common on the right

•  Risk of injury is higher for a 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 the more active form (is tyrosine + iodine)

•  Most T3 is produced in periphery from T4 to T3 conversion by deiodinases

  Peroxidases link iodine and tyrosine together

  Deiodinases separate iodine from tyrosine

  Thyroxine-binding globulin – thyroid hormone transport; binds the majority of T3 and T4 in circulation

  TSH – most sensitive indicator of gland function

  Tubercles of Zuckerkandl – most lateral, posterior extension of thyroid tissue

•  Rotate medially to find RLNs

•  This portion is left behind with subtotal thyroidectomy because of proximity to RLNs

  Parafollicular C cells – produce calcitonin

  Thyroxine treatment – TSH levels should fall 50%; osteoporosis 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

THYROID STORM

  Symptoms: ↑ HR, fever, numbness, irritability, vomiting, diarrhea, high-output cardiac failure (most common cause of death)

  Most common after surgery in patient with undiagnosed Graves’ disease

  Can be precipitated by anxiety, excessive gland palpation, adrenergic stimulants

  Tx: β-blockers (first line), PTU, Lugol’s solution (KI), cooling blankets, oxygen, glucose

•  Emergent thyroidectomy rarely indicated

  Wolff–Chaikoff effect – very effective for thyroid storm; patient given high doses 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

  90% of thyroid nodules are benign; female predominance

  Get FNA (best initial test) and thyroid function tests

•  Determinant in 80% → follow appropriate treatment

•  Shows follicular cells → lobectomy (10% CA risk; see Thyroid CA section)

•  Shows thyroid CA → thyroidectomy or lobectomy and appropriate treatment (see Thyroid CA section)

•  Shows cyst fluid → drain fluid

•  If it recurs or is bloody → lobectomy

•  Shows colloid tissue → most likely colloid goiter; low chance of malignancy (< 1%)

•  Tx: thyroxine; lobectomy if it enlarges

•  Shows normal thyroid tissue and TFTs are elevated → likely solitary toxic nodule

•  Tx: if asymptomatic can just monitor; PTU and ¹³¹I if symptomatic

•  Indeterminant in 20% → get radionuclide study

•  Hot nodule → Tx: if asymptomatic can monitor; PTU and ¹³¹I if symptomatic

•  Cold nodule → lobectomy (more likely malignant than hot nodule)

  Goiter

•  Any abnormal enlargement

•  Most identifiable cause is iodine deficiency; Tx: iodine replacement

•  Diffuse enlargement without evidence of functional abnormality = nontoxic colloid goiter

•  Unusual to have to operate unless goiter is causing airway compression or there is a suspicious nodule

•  Tx: subtotal or total thyroidectomy for symptoms or if suspicious nodule; subtotal has decreased risk of RLN injury

  Substernal goiter

•  Usually secondary (vessels originate from superior and inferior thyroid arteries)

•  Primary substernal goiter – rare (vessels originate from innominate artery)

Stay updated, free articles. Join our Telegram channel

Join