Pathology of the pituitary

Question 1

Anterior vs posterior lobes of the pituitary

Answer 1

• Anterior: adenohypophysis, origin is rathke pouch, blood supply is venous portal system (vulnerable to ischemia)
• Cell types: chromophobes, acidophils (somatotropes, lactotropes), basophils (corticotrophs, thyrotrophs, gonadotrophs)
• Ectopic or remnant squamous tissue from rathke pouch may give rise to caniopharyngiomas
• Posterior: neurohypophysis, origin is diencephalon, arterial blood supply
• Pituicytes: ADH and oxytocin

Question 2

Congenital anomalies of pituitary

Answer 2

• Aplasia: defective rathke pouch formation
• Posterior lobe is present but anterior lobe absent
• There is end organ hypoplasia
• Anencephaly: anterior lobe present but posterior lobe absent
• Pharyngeal pituitary: congenital rest (remnant of rathke pounch) in midline of nasopharynx
• Can be a source of ectopic pituitary adenoma

Question 3

Pituitary apoplexy

Answer 3

• Sudden hemorrhage/infarction followed by necrosis
• Most common underlying disease is macro adenoma
• Neurosurgical emergency
• 75-90% destruction of anterior pituitary causes hypopituitarism

Question 4

Sheehan syndrome (postpartum pituitary necrosis)

Answer 4

• Only affects anterior lobe (more vulnerable to ischemia)
• Durin pregnancy there is enlargement of pituitary to 2x normal size
• During pregnancy there may be blood loss/shock and thus decreased perfusion to pituitary
• Anterior lobe is susceptible to ischemia-> infarction-> necrosis
• May lead to hypopituitarism

Question 5

Chronic inflammation of pituitary

Answer 5

• Granulomatous diseases: TB, sarcoid, syphilis, fungal
• Lymphocytic hypophysitis: usually occurs during pregnancy or just after birth (affects both sexes but prefers women)
• Autoimmune infiltration of pituitary by lymphocytes w/ destruction and fibrosis
• May result in an enlarged gland that produces pressure Sx (bitemporal hemianopsia, headaches, nausea/vomiting, enlargement of sella)
• Associated w/ hashimoto thyroiditis, when pt has both its polyglandular autoimmune syndrome (may have adrenal and pancreatic involvement)

Question 6

Pituitary adenomas 1

Answer 6

• May be functional or nonfunctional, micro (10mm) adenomas

- Functional micro adenomas typically produce serum levels 100 of the functional hormone

Question 7

Pituitary adenomas 2

Answer 7

• Non functional macro adenomas may cause the stalk affect/compression/hemorrhage, which can lead to hypopit
• Stalk effect will have a prolactin level in the micro range (<100) due to ceasing the DA inhibition
• Pituitary adenomas are associated w/ MENI: pituitary adenomas, parathyroid hyperplasia, pancreatic islet cell neoplasms (PPP; chrom 11q13)

Question 8

Pathology of pituitary adenomas 1

Answer 8

• Most are nonfunctional (chromophobe adenomas), of the functional adenomas prolactinomas are most common
• Macroadenomas have significantly high risk of apoplexy
• Micro: very uniform cell population (compared to variability of normal ant pituitary cell histology), few mitoses, high nuclear pleomorphism
• Prolactinomas produce infertility, amenorrhea, +/- galactorrhea (first two b/c high prolactin reduces FSH/LH secretion)
• GH producing tumors lead to gigantism (proportionate growth) if they occur before epiphyses close, or acromegaly (disproportionate growth) if after the epiphyses close (adulthood)

Question 9

Pathology of pituitary adenomas 2

Answer 9

• Corticotroph adenomas: most are micro adenomas, produce cushiness disease
• Nelson syndrome: rapidly enlarging pituitary tumor and skin hyper pigmentation occurring in cushiness disease pts previously Rx w/ bilateral adrenalectomy
• ACTH producing cells undergo Crook’s hyaline change when there is cushings-induced adenoma
• The cytoplasm becomes a glassy pink ring around the nucleus
• Pituitary CA is very rare and most are nonfunctional (usually are mets from somewhere else)

Question 10

Craniopharyngioma

Answer 10

• Arises from epithelial remnants of rathke pouch, usually suprasellar producing pressure Sx
• Mostly affects young (children and adolescents) and those in 6th decade, frequently shows calcification
• Micro: squamous epithelial cysts, calcification, cholesterol crystals, stellate mesenchymal center, and pallisading nuclei around empty spaces are common
• Calcified cystic suprasellar mass in young person is craniopharyngioma until proven otherwise
• Difficult to resect and recurrence is common

Question 11

Posterior pituitary pathology 1

Answer 11

• Normal histology of post pit: looks like neural tissue (neuropil)
• DI: nephrogenic DI due to kidneys resistant to ADH, central DI due to no ADH release
• SIADH: increased ADH release, from stress, trauma, pituitary dysfxn, tumors (small cell CA)
• Mets most likely go to post lobe than ant lobe (breast/lung)
• Inflammatory conditions: encephalitis, sarcoid, TB, siphilis

Question 12

Posterior pituitary pathology 2

Answer 12

• Trauma: basal skull fracture-> damage to neurohypophysis
• Langerhans cell histiocytosis: granulomatous, destructive lesion that under LM looks like histiocyte infiltration of post pit
• Under EM can see zipper-like structures w/in cells (birbeck granules), cells are CD1a and S100 positive
• Hand-schuller-christian disease: langerhans cell histiocytosis that causes bony lesions, exopthalmos, and DI

Question 13

Empty sella syndrome

Answer 13

• Primary: compression atrophy of the pituitary due to arachnoid herniation containing CSF thru defect in sella (CSF pooch)
• Rarely causes hypopituitarism
• Secondary: due to spontaneous necrosis or surgical removal of pituitary adenoma, leads to hypopit