Parafollicular C cells:

  • Derived from neural crest
  • Produce calcitonin (decrease serum calcium)

T3: is 3 times as active as T4,

  • Half-life = 3 days

FT4: T3RU timesT4


  • Prevents DIT, MIT coupling
  • Crosses placenta -> cretinism
  • Rare but dreaded aplastic anemia

Peripheral conversion of T4 to T3 Blockers:

  • PTU, Propranolol, Prednisone (& other steroids)

Wolk Chaikoff effect: high I-doses (lugol's, KI)

  • Inhibit TSH
  • Useful in thyroid storm

FNA: Cannot distinguish malignant/benign with è Follicular and Hurthle cell è need tissue

Papillary Thyroid CA: most common (85%, P for Popular)

  • Lymphatic spread but nodes don't predict survival.
  • 20% of adults, 80% of children present node positive
  • 80% are Multicentric.
  • Psammoma bodies on path (P again), represents deposited calcium
  • History of exposure to radiation increases risk
  • F:M ratio is 3:1
  • 1/2 are before age 40
  • Lateral aberrant thyroid rest = nl appearing thyroid in a neck node = papillary thyroid cancer
  • MACIS criteria: criteria for
  • Mets:
    • ​Age (M>50, F>40 is worse)
    • Completeness of resection
    • Invasiveness and Size (>1.5cm generally means total thyroidectomy needed)

Follicular Thyroid CA:

  • Spreads hematogenously
  • 60% present with mets.
  • Present a little older (50s)
  • Also F:M 3:1.
  • Needle dx not adequate.
  • Generally do total thyroidectomy with ablative RI post-op

Medullary Thyroid CA (MTC):

  • 20% have MEN2
  • (Tend to be bilateral, younger, worse prognosis)
  • See amyloid on path (pathognomonic)
  • Gastrin is used as provocative test for Medullary thyroid CA (increase calcitonin)
  • Originates from parafollicular C cells.
  • Ret proto-oncogene is diagnostic.
  • Tx = total thyroidectomy, neck dissection if node (+)

Cold nodule lesion more likely Cancer than hot lesion

  • 1st step in work-up of thyroid nodule after H&P is FNA

Pregnancy: No radioactive iodine during pregnancy.

  • Operate in 2nd trimester if possible.

Radioactive iodine: Only useful for well-differentiated tumors (papillary and follicular)

Superior laryngeal nerve, external branch:

  • Motor: to cricothyroid muscle
  • Injury = loss of projection, high pitch (vocal folds cannot be tightened)
  • Provides sensory: to supraglottis

Recurrent laryngeal nerve:

  • Innervates all of larynx except cricothyroid.
  • Injury to one branch: hoarseness
  • Bilateral injury = occluded airway


  • Supernumerary parathyroid 15%
  • Mediastinal gland blood supply from internal mammary or branches within the thyroid

Superior parathyroids: From 4th pouch

Inferior parathyroids: (and thymus) from 3rd

  • Inferior more variable position

All parathyroids generally receive blood supply from inferior thyroid artery

N terminal is active, C terminal is inactive portion of hormone (as with insulin)


  • Increase calcium bind protein to
  • Increase gut absorption of CA
  • Increase kidney Ca absorption
  • Increase PO4 loss


  • A/w prad oncogene and h/o radiation exposure
  • Increased Ca, Decreased Ph; Cl- to Ph ratio > 33:1
  • Osteitis fibrosa cystica is pathognomonic for hyper-PTH
  • Check urine Ca, should be high (r/o FHH = familal hypocalciuric hypercalcemia)
  • Most patients are asymptomatic, found incidentally with high Ca
  • 85% have single gland adenoma (except in MEN where increase PTH is due to 4 gland hyperplasia)
  • Tx of hypercalcemia crisis:
  • Dehydration IV hydration with NS
  • Furosemide Na+ and Ca+ exretion
  • Rare parathyroid adenocarcinoma:
  • Palpable mass
  • Very high Ca++
  • Resect widely

Multiple Endocrine Neoplasia

(MEN I) PPP pancreatic islet cell, pituitary, hyperparathyroidism

  • Pituitary adenoma
  • Hyperplasia of Parathyroid (not adenoma)
  • Pancreatic tumor
  • Gastrinoma 50%
  • Peptic ulcer, diarrhea
  • Insulinoma 20%
  • Confusion, seizure, personality change, palpitations, diuresis, hypoglycemia

MEN IIa 2 MPH: Medullary, Pheo, hyperparathyroidism

  • Medullary thyroid CA
  • Pheo
  • Hyperparathryroid

MEN IIb Medullary, Pheo, Mucosal neuroma, Marfans

  • Medullary thyroid CA
  • Calcitonin
  • Pheo
  • Urinary catecholamine, HTN
  • Mucosal neuroma
  • Marfans

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