A 28-year-old woman presents to her primary care physician complaining of intense thirst and frequent urination for the past 2 weeks. She says that she constantly feels the urge to drink water and is also going to the bathroom to urinate frequently throughout the day and multiple times at night. She was most recently hospitalized 1 month prior to presentation following a motor vehicle accident in which she suffered severe impact to her head. The physician obtains laboratory tests, with the results shown below: Serum: Na+: 149 mEq/L Cl-: 103 mEq/L K+: 3.5 mEq/L HCO3-: 24 mEq/L BUN: 20 mg/dL Glucose: 105 mg/dL Urine Osm: 250 mOsm/kg The patient’s condition is most likely caused by inadequate hormone secretion from which of the following locations?

Preoptic nucleus of the hypothalamus

Suprachiasmatic nucleus of the hypothalamus

Four months after giving birth, a young woman presents to the hospital complaining of lack of breast milk secretion. The patient complains of constantly feeling tired. Physical exam reveals that she is slightly hypotensive and has lost a significant amount of weight since giving birth. The patient states that she has not experienced menstruation since the birth. Which of the following is likely to have contributed to this patient's presentation?

Increased anterior pituitary perfusion

Pregnancy-induced decrease in anterior pituitary size

A previously healthy 46-year-old man comes to the physician for an 8-month history of headache that is more severe in the mornings. His blood pressure is 151/92 mm Hg. Examination shows enlargement of the nose, forehead, and jaw as well as the hands, fingers, and feet. Ophthalmologic examination shows impaired vision in the outer peripheral fields of both eyes. Laboratory studies show a serum glucose concentration of 225 mg/dL. Which of the following findings is most likely to confirm the diagnosis?

Elevated serum insulin-like growth factor-1 level

A 34-year-old woman, who had her first child 2 weeks ago, visits her family physician with concerns about constant fatigue and difficulty with breastfeeding. She was discharged from the intensive care unit after hospitalization for severe postpartum hemorrhage. Since then, she has tried multiple pumps and self-stimulation to encourage breast milk production; however, neither of these strategies has worked. Her blood pressure is 88/56 mm Hg and heart rate is 120/min. Which of the following best explains the underlying condition of this patient?

Pituitary infiltration by histiocytes

Pituitary stalk epithelial tumor

A 47-year-old woman complains of weight gain and irregular menses for the past 2 years. She has gained 13 kg (28.6 lb) and feels that most of the weight gain is in her abdomen and face. She has type 2 diabetes and hypertension for 1 year, and they are difficult to control with medications. Vital signs include a temperature of 36.9°C (98.4°F), blood pressure of 160/100 mm Hg, and pulse of 95/min. The patient's late-night salivary cortisol is elevated. Morning plasma ACTH is high. Brain magnetic resonance imaging shows a 2 cm pituitary adenoma. Which of the following is the optimal therapy for this patient?

Transsphenoidal pituitary adenomectomy

A 48-year-old man is brought to the emergency department by his neighbor, who found him lying unconscious at the door of his house. The patient lives alone and no further history is available. On physical examination, his temperature is 37.2ºC (98.9ºF), pulse rate is 114/min, blood pressure is 116/78 mm Hg, and respiratory rate is 22/min. His Glasgow Coma Scale score is 7 and the patient is intubated. A stat serum osmolality is reported at 260 mmol/kg. Based on the provided information, which of the following conditions is most likely present in this patient?

Syndrome of inappropriate antidiuretic hormone

Nonketotic hyperosmolar hyperglycemic coma

A 71-year-old male presents to the emergency department after having a generalized tonic-clonic seizure. His son reports that he does not have a history of seizures but has had increasing confusion and weakness over the last several weeks. An electrolyte panel reveals a sodium level of 120 mEq/L and a serum osmolality of 248 mOsm/kg. His urine is found to have a high urine osmolality. His temperature is 37° C (98.6° F), respirations are 15/min, pulse is 67/min, and blood pressure is 122/88 mm Hg. On examination he is disoriented, his pupils are round and reactive to light and accommodation and his mucous membranes are moist. His heart has a regular rhythm without murmurs, his lungs are clear to auscultation bilaterally, the abdomen is soft, and his extremities have no edema but his muscular strength is 3/5 bilaterally. There is hyporeflexia of all four extremities. What is the most likely cause of his symptoms?

Syndrome of Inappropriate Antidiuretic Hormone (SIADH)

Pituitary disorders for USMLE Step 2 CK: High-Yield Pathology Lessons

Pituitary Anatomy - Command Center

Location: Protected within the sella turcica of the sphenoid bone.
Lobes & Embryology:
- Anterior (Adenohypophysis): From oral ectoderm (Rathke's pouch).
- Posterior (Neurohypophysis): From neuroectoderm.
Anterior Pituitary Hormones: 📌 FLAT PEG
- Tropic: FSH, LH, ACTH, TSH
- Direct: Prolactin, Endorphins, GH

⭐ Pituitary adenomas can compress the optic chiasm superiorly, causing classic bitemporal hemianopsia.

Pituitary Adenomas - Hyperactive Hormones

Prolactinoma (Most Common):
- Secretes ↑ Prolactin → Galactorrhea & amenorrhea (females), ↓ libido & infertility (males).
- Dx: ↑ serum prolactin.
- Rx: Dopamine agonists (e.g., Cabergoline, Bromocriptine).
Somatotroph Adenoma (↑ GH):
- Acromegaly (Adults): Large hands/feet, coarse facial features, insulin resistance.
- Gigantism (Children): ↑ linear growth before epiphyseal closure.
- Dx: ↑ IGF-1; failure of GH suppression with oral glucose tolerance test.
Corticotroph Adenoma (↑ ACTH):
- Cushing's Disease: The specific cause of Cushing's syndrome due to a pituitary adenoma.
- Dx: ↑ 24-hr urine free cortisol; failure of low-dose dexamethasone suppression.

⭐ Nelson Syndrome: Post-bilateral adrenalectomy, a pre-existing corticotroph adenoma grows rapidly. Presents with mass effects and hyperpigmentation (↑ MSH).

Acromegaly: Signs and Symptoms

Posterior Pituitary - Wet or Dry

SIADH (Wet - ↑ ADH): Euvolemic hyponatremia.
- Causes: Ectopic (Small cell lung cancer), CNS trauma, drugs.
- Labs: ↓ Serum Osm, ↑ Urine Osm (>100 mOsm/kg), ↑ Urine Na+ (>40 mEq/L).
- 📌 Small cell, Increased ADH, Dilutional Hyponatremia.
Diabetes Insipidus (Dry - ↓ ADH effect): Hypernatremia & polyuria.
- Central: ↓ ADH production. Responds to desmopressin.
- Nephrogenic: Renal ADH resistance. No response.

⭐ Correcting hyponatremia from SIADH too rapidly (>8-12 mEq/L/24h) risks osmotic demyelination syndrome (central pontine myelinolysis).

Hypopituitarism - Powering Down

Etiology: Pituitary adenomas (most common), Sheehan syndrome (postpartum necrosis), apoplexy, empty sella syndrome, craniopharyngioma.
Clinical Presentation: Sequential loss of hormones.
- ↓GH → Dwarfism (children)
- ↓FSH/LH → Amenorrhea, ↓libido
- ↓TSH → Secondary hypothyroidism
- ↓ACTH → ↓cortisol, no hyperpigmentation
📌 Sequence of Loss: Go Look For The Adenoma (GH, LH, FSH, TSH, ACTH)

Sheehan Syndrome Pathophysiology

⭐ In pituitary-dependent adrenal insufficiency (↓ACTH), aldosterone levels are preserved by the renin-angiotensin system, but cortisol is low.

Craniopharyngioma - Rathke's Revenge

Benign suprasellar tumor from Rathke's pouch remnants (ectoderm).
Bimodal age distribution: common in children (5-15 yrs) & adults (>50 yrs).
Presents with headaches, visual defects (bitemporal hemianopsia), and panhypopituitarism.
Histology: "Wet" keratin, dystrophic calcification, and cysts with "machine oil" fluid (cholesterol crystals).

⭐ Most common childhood supratentorial tumor.

High‑Yield Points - ⚡ Biggest Takeaways

Pituitary adenomas are the most common cause of hyperpituitarism; prolactinomas are the most frequent type.

Mass effect from adenomas classically causes bitemporal hemianopsia by compressing the optic chiasm.

Sheehan syndrome is postpartum pituitary necrosis, leading to hypopituitarism and failure to lactate.

Central Diabetes Insipidus (↓ ADH) causes polyuria and hypernatremia; it responds to desmopressin.

SIADH (↑ ADH) results in euvolemic hyponatremia and inappropriately concentrated urine.

Pituitary apoplexy, an acute hemorrhage into an adenoma, is a neurosurgical emergency.

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