Pituitary Pathology

Question 1

What are the types of pituitary adenomas? How common is each? How do patients present?

Answer 1

• pituitary adenomas are benign and can be functional (about 70%) or nonfunctional (about 30%)
• 40% are prolactinomas (most common)
• 20% are somatotrophic (GH)
• 10% are corticotrophin (ACTH)
• adenomas secreting TSH, FSH, or LH are very rare
• patients present with mass effect: bitemporal hemianopia, hypopituitarism, headache (if the tumor is functional, patients will also present with effects of the excess hormone)

Question 2

How do patients with a prolactinoma present?

Answer 2

• prolactinoma is the most common type of pituitary adenoma; it secretes prolactin
• women: galactorrhea, secondary amenorrhea*
• men: impotence* and decreased libido*
• *prolactin INHIBITS GnRH secretion from the hypothalamus, resulting in an inhibition of FSH and LH secretion

Question 3

How do patients with a somatotrophic pituitary adenoma present?

Answer 3

• somatotrophes secrete growth hormone
• in kids: gigantism and eventual cardiac failure
• in adults: acromegaly; patients present with large tongues, deep voices, large hands and feet, coarse facies (frontal bossing, jaw protrusion, spacing between teeth), insulin resistance

Question 4

How do we diagnose acromegaly? How can we treat it? What is the most common cause of death in these patients?

Answer 4

• pituitary mass on MRI
• elevated serum IGF-1 (AKA somatomedin C; hepatic synthesis triggered by GH)
• failure to suppress GH in an oral glucose tolerance test (normally, glucose inhibits GH secretion)
• treat with surgery and/or octreotide (a somatostatin analog; somatostatin inhibits GH secretion)
• most common cause of death is dilated cardiomyopathy

Question 5

What is diabetes insipidus? How to patients present? What are the two types?

Answer 5

• diabetes insipidus is the inability to concentrate urine due to a dysfunction in ADH (AKA vasopressin)
• patients present with polyuria and polydipsia; serum osmolarity is increased and hyperosmotic volume contraction occurs (euvolemic hypernatremia; loss of H2O)
• 2 types: central and nephrogenic

Question 6

What causes central diabetes insipidus? Is ADH high or low? How do we treat it?

Answer 6

• central DI is due to an issue with the posterior pituitary gland’s secretion of ADH (vasopressin)
• causes: pituitary adenoma, autoimmune damage, trauma, surgery, Sheehan syndrome, etc.
• ADH is low in these patients
• treat with hydration and DDAVP (desmopressin, an ADH analog)

Question 7

What causes nephrogenic diabetes insipidus? Is ADH high or low? How do we treat it?

Answer 7

• nephrogenic DI is due to an issue with the kidney’s sensitivity to ADH (vasopressin)
• causes are hereditary (defect in V2 receptor for ADH), hypercalcemia, lithium
• ADH is normal or high in these patients
• treat with hydration, hydrochlorothiazide, indomethacin, amiloride

Question 8

What is SIADH? What are the major causes? How do patients present?

Answer 8

• SIADH: syndrome of inappropriate ADH secretion
• excessive ADH results in excessive water retention and lowered serum osmolarity (euvolemic hyponatremia)
• aldosterone decreases in response to the water retention, leading to decreased Na+ reabsorption and hyponatremia
• causes: ectopic ADH secretion (in small cell lung carcinoma), CNS disorder or head trauma, drugs

Question 9

How do we treat SIADH? What is a potential complication of treatment?

Answer 9

• treat SIADH with fluid restriction
• give IV hypertonic saline to restore Na+*
• can also give demeclocycline (an ADH antagonist)
• *the rapid uptake of Na+ during treatment can result in pontine myelinolysis (irreparable damage to pons) AKA “locked in” syndrome; prevent this by slowly correcting the patient’s sodium

Question 10

What are the major causes of hypopituitarism? What is the most common cause in adults? In children?

Answer 10

• nonfunctional pituitary adenoma (MCC in adults)
• craniopharyngioma (MCC in children)
• Sheehan syndrome
• empty sella syndrome
• hemorrhage (pituitary apoplexy)
• autoimmune destruction (lymphocytic hypophysitis)
• (anything that destroys the tissue)
• secondary hypopituitarism is via a defect in hypothalamus

Question 11

What is Sheehan syndrome? Empty sella syndrome? Pituitary apoplexy?

Answer 11

• these all cause hypopituitarism
• Sheehan: postpartum ischemic infarct of pituitary due to hypovolemic shock (partum blood loss)
• empty sella: subarachnoid space extends into the sella turcica, the increased pressure (from the CSF in the SAS) flattens and destroys the pituitary gland; common in obese women
• pituitary apoplexy: hemorrhage of pituitary; sudden onset of neurologic and hormone dysfunction (BP collapse, profound lethargy, potential severe headache)