Pituitary Disorders

Pituitary Basics - Master Gland Overview

• Location: Sella turcica, sphenoid bone; connected to hypothalamus by infundibulum (stalk).
• Lobes & Hormones:
  • Anterior (Adenohypophysis): GH, PRL, ACTH, TSH, FSH, LH. 📌 Mnemonic: FLAT PiG (FSH, LH, ACTH, TSH, PRL, GH).
  • Posterior (Neurohypophysis): Stores & releases ADH (Vasopressin), Oxytocin (from hypothalamus).
• Regulation: Hypothalamic releasing/inhibiting factors (anterior); neural input (posterior).

⭐ The anterior pituitary develops from Rathke's pouch (oral ectoderm); posterior from neuroectoderm (diencephalon).

Anterior Hyperdrive - Excess Hormone Express

Pituitary adenomas causing hormone overproduction.

• Prolactinoma (Most Common)

  • Symptoms: Galactorrhea, amenorrhea, infertility, ↓libido.
  • Diagnosis: ↑Serum PRL. PRL > 200 ng/mL suggestive. MRI.
  • Treatment: Dopamine agonists (Cabergoline > Bromocriptine). Surgery if failure/compression.

• Acromegaly / Gigantism (GH Excess)

  • Gigantism (kids), Acromegaly (adults).
  • Symptoms: Coarse facies, large hands/feet, prognathism, arthralgia, HTN, DM.
  • Diagnosis: ↑IGF-1 (screen). OGTT: GH not suppressed < $\mathbf{1}$ ng/mL (confirm). MRI.
  • Treatment: Transsphenoidal surgery (1st line). Medical: Somatostatin analogs (Octreotide), Pegvisomant.

• Cushing's Disease (ACTH-secreting adenoma)

  • Symptoms: Central obesity, moon facies, buffalo hump, purple striae, HTN, hyperglycemia, osteoporosis.
  • Diagnosis: ↑ACTH. Low-dose dexamethasone: no suppression; high-dose: suppression. MRI.
  • Treatment: Transsphenoidal surgery (1st line). Medical: Ketoconazole, Metyrapone.

⭐ Prolactinomas are the most common hormone-secreting pituitary tumors.

Anterior Low & Slow - Deficits & Pressure Cookers

• Hypopituitarism (Deficits): ↓Anterior pituitary hormones.
  • Causes: Adenomas, Sheehan's, apoplexy, iatrogenic (surgery/XRT).
  • 📌 Order of loss: GH → LH/FSH → TSH → ACTH → PRL ("Go Look For The Adenoma").
  • Clinical Features:
    • GH↓: Child: dwarfism; Adult: ↓muscle, ↑fat, ↓QoL.
    • LH/FSH↓: Hypogonadism (amenorrhea, infertility, ↓libido).
    • TSH↓: Secondary hypothyroidism (fatigue, cold).
    • ACTH↓: Secondary adrenal insufficiency (weakness, hypotension; NO hyperpigmentation/hyperkalemia).
    • PRL↓: Lactation failure.
• Pressure Cookers (Tumor Mass Effects): Expanding pituitary lesions.
  • Headache: Often bitemporal.
  • Visual: Bitemporal hemianopia (optic chiasm).
  • CN Palsies: CN III, IV, V1/2, VI palsies (cavernous sinus).
  • Pituitary Apoplexy: Acute tumor bleed/infarct. Severe HA, vision loss, ophthalmoplegia, ↓LOC. Emergency!
  • Sheehan's Syndrome: Postpartum necrosis. Lactation failure, amenorrhea, hypopituitarism.

    ⭐ ACTH deficiency: Aldosterone (RAAS) normal → NO hyperkalemia. Low ACTH/MSH → NO hyperpigmentation.

Posterior Pituitary - Water Works Wonders (or Woes)

ADH (Vasopressin) from posterior pituitary controls water balance.

• Diabetes Insipidus (DI): 📌 "Dry Inside" - ↓ADH effect.
  • Symptoms: Polyuria (>3L/day), polydipsia, nocturia.
  • Labs: ↑Serum Osm (>295 mOsm/kg), ↓Urine Osm (<300 mOsm/kg), ↓Urine Sp. Gr. (<1.005).
  • Types:
    • Central (↓ADH): Rx Desmopressin. Dx: Water deprivation test + ADH.
    • Nephrogenic (Kidney ADH resistance): Rx Thiazides, Amiloride (Li-induced).
• SIADH: 📌 "Soaked Inside" - ↑ADH effect.
  • Symptoms: Related to hyponatremia (Na <135 mEq/L); euvolemic.
  • Labs: ↓Serum Osm (<275 mOsm/kg), ↑Urine Osm (>100 mOsm/kg), ↑Urine Na (>20 mEq/L).
  • Rx: Fluid restriction (<800mL/day), hypertonic saline (severe), Vaptans.

  ⭐ Ectopic ADH from Small Cell Lung Cancer is a classic cause of SIADH.

High‑Yield Points - ⚡ Biggest Takeaways

• Prolactinoma: Most common functional pituitary adenoma; treat with dopamine agonists (cabergoline).
• Acromegaly/Gigantism: Screen with IGF-1; confirm with OGTT (failed GH suppression).
• Cushing's Disease: ACTH-secreting pituitary adenoma; leads to bilateral adrenal hyperplasia.
• Central Diabetes Insipidus: ↓ADH secretion; water deprivation test confirms; responds to desmopressin.
• SIADH: Characterized by euvolemic hyponatremia; primary treatment is fluid restriction.
• Sheehan's Syndrome: Postpartum pituitary ischemic necrosis causing panhypopituitarism.
• Craniopharyngioma: Suprasellar calcified cystic tumor (Rathke's pouch remnant); visual field defects_._