Everything You Need to Know About Pituitary adenomas (prolactinoma, GH-secreting) for Step 1

Pituitary adenomas are one of those “small lesion, huge consequences” topics that USMLE loves: a tiny tumor in the sella can derail reproduction, growth, vision, and even your glucose control. The good news is that Step questions are very pattern-based—if you recognize the hormone profile + clinical syndrome + MRI findings, you can usually nail diagnosis and first-line treatment quickly.

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Big picture: what is a pituitary adenoma?

A pituitary adenoma is a usually benign neoplasm arising from anterior pituitary hormone–producing cells.

Key definitions (high-yield)

• Microadenoma: < 10 mm
• Macroadenoma: ≥ 10 mm (more likely to cause mass effect, especially bitemporal hemianopsia)

Why Step 1 cares

Pituitary adenomas show up in questions as:

• Hyperfunctioning tumors (e.g., prolactinoma, GH-secreting adenoma)
• Mass effect symptoms (headache, visual field defects)
• Hypopituitarism from compression of normal pituitary tissue (esp. with macroadenomas)

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First Aid cross-ref (Endocrine → Pituitary): pituitary adenomas, prolactinoma, acromegaly/gigantism, stalk effect, bitemporal hemianopsia.

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Anatomy + physiology quick refresh (what to localize on exams)

Pituitary neighborhood

• Pituitary sits in the sella turcica, just inferior to the optic chiasm
• Macroadenoma can compress optic chiasm → classically bitemporal hemianopsia
• Compression of pituitary stalk can disrupt hypothalamic dopamine delivery

Hypothalamic control (especially testable with prolactin)

• Dopamine inhibits prolactin (tonic inhibition)
• TRH stimulates prolactin (and TSH)

So if something decreases dopamine to the pituitary (e.g., stalk compression), prolactin can rise even without a prolactinoma.

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Two Step superstars: Prolactinoma and GH-secreting adenoma

At-a-glance comparison table

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Prolactinoma: deep dive

Pathophysiology

A prolactinoma is a lactotroph adenoma producing excess prolactin, which:

• Suppresses GnRH → ↓ LH/FSH
• Leads to hypogonadism (amenorrhea/oligomenorrhea, infertility, ↓ libido, ED)
• Causes galactorrhea (may be present in men too, but less emphasized)

Clinical presentation (classic vignettes)

Women:

• Amenorrhea/oligomenorrhea
• Galactorrhea
• Infertility
• Low estrogen symptoms (vaginal dryness, decreased bone density over time)

Men:

• Decreased libido
• Erectile dysfunction
• Infertility
• Often present later with macroadenoma symptoms (headache/visual defects)

Mass effect (macroadenoma):

• Headache
• Bitemporal hemianopsia
• Possible hypopituitarism (compression)

Diagnosis (USMLE-style algorithm)

1. Check serum prolactin
2. Rule out common secondary causes before labeling it “prolactinoma”:
   • Pregnancy (always check)
   • Medications: dopamine antagonists (e.g., antipsychotics like risperidone/haloperidol), metoclopramide
   • Primary hypothyroidism: ↑ TRH → ↑ prolactin
     • Order TSH/free T4 if suggested
3. Pituitary MRI with contrast
   • Especially if prolactin is markedly elevated or symptoms suggest a sellar mass

HY nuance: “stalk effect” vs prolactinoma

• Stalk compression decreases dopamine delivery → mild to moderate prolactin elevation
• True prolactinoma tends to have higher prolactin levels and a lesion arising from lactotrophs
  (Exact numeric cutoffs vary; on Step, think very high prolactin = prolactinoma, modest elevation = stalk effect/meds/hypothyroid.)

Treatment

First-line: dopamine agonists

• Cabergoline (often preferred: more potent/longer-acting)
• Bromocriptine (classically tested, especially in pregnancy contexts)

These:

• ↓ prolactin
• Shrink tumor size (often dramatically)
• Restore gonadal function

Surgery (transsphenoidal)

• Consider if medication fails, not tolerated, or if there are urgent compressive symptoms not responding quickly.

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GH-secreting adenoma: deep dive (acromegaly/gigantism)

Pathophysiology

A somatotroph adenoma secretes GH, which stimulates the liver to produce IGF-1 (somatomedin C).
Most of the chronic “growth” effects are mediated by IGF-1.

• Adults (closed epiphyses) → acromegaly
• Children (open epiphyses) → gigantism

Clinical presentation (what Step expects you to recognize)

Acromegaly (adults):

• Enlarged hands/feet (rings/shoes no longer fit)
• Coarse facial features, prognathism (jaw growth)
• Macroglossia
• Increased sweating, oily skin
• Carpal tunnel syndrome
• Organomegaly
• Headaches, visual field defects (macroadenoma)

Metabolic/cardiopulmonary associations (high-yield):

• Insulin resistance → impaired glucose tolerance/DM
• Hypertension
• Cardiomyopathy (can be a cause of mortality)
• Obstructive sleep apnea
• Increased risk of colon polyps (and possibly colon cancer—often tested as “needs colonoscopy”)

Diagnosis

Best screening test: serum IGF-1

• More stable than GH (GH is pulsatile)

Confirmatory test: oral glucose suppression test

• Normal physiology: glucose load → suppresses GH
• Acromegaly: GH fails to suppress (remains elevated)

Imaging: pituitary MRI

• Often shows a macroadenoma

Treatment

First-line (typical): transsphenoidal resection (especially for resectable tumors)

Medical therapy (adjunct or if not surgical candidate / persistent disease):

• Somatostatin analogs: octreotide, lanreotide (↓ GH release)
• GH receptor antagonist: pegvisomant (blocks GH action → ↓ IGF-1 effects)
• Dopamine agonists (less effective, but can help in select cases, especially mixed tumors)

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Shared mass effects and complications (very testable)

Optic chiasm compression

• Bitemporal hemianopsia is the classic pattern
• Often paired with headaches and endocrine symptoms in vignettes

Hypopituitarism from compression

A large adenoma can compress normal pituitary tissue leading to low downstream hormones:

• Secondary adrenal insufficiency (low ACTH/cortisol)
• Secondary hypothyroidism (low TSH → low T4)
• Hypogonadotropic hypogonadism (low LH/FSH)
• Prolactin can be paradoxically elevated via stalk effect even in non-prolactin tumors

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High-yield differentials and traps

1) Medication-induced hyperprolactinemia

• Dopamine blockade (antipsychotics, metoclopramide) → ↑ prolactin
• Look for psych history + galactorrhea/amenorrhea

2) Primary hypothyroidism

• ↑ TRH → ↑ prolactin
• Clues: weight gain, cold intolerance, constipation, bradycardia; labs show ↑ TSH, ↓ free T4
• Treat hypothyroidism → prolactin often normalizes

3) Physiologic hyperprolactinemia

• Pregnancy and lactation (don’t miss the pregnancy test in a vignette)

4) Pituitary apoplexy (board-relevant emergency)

Hemorrhage into a pituitary adenoma → sudden:

• Severe headache
• Visual symptoms/ophthalmoplegia
• Acute hypopituitarism (can cause adrenal crisis)

Management often includes urgent steroids + neurosurgical evaluation.

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Step-ready “if you see X, think Y” associations

• Amenorrhea + galactorrhea + infertility → check prolactin, consider prolactinoma
• Bitemporal hemianopsia + endocrine symptoms → think pituitary macroadenoma
• Big hands/feet + coarse facial features + new diabetes → check IGF-1, confirm with glucose suppression test
• Elevated prolactin + antipsychotic use → medication effect (don’t jump straight to surgery)
• Elevated prolactin + hypothyroid symptoms → check TSH/free T4 (TRH-driven prolactin)

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First Aid cross-references (quick map for your review)

While edition page numbers vary, these topics live in:

• Endocrine → Hypothalamus & Pituitary
  • Prolactin regulation (dopamine inhibits; TRH stimulates)
  • Prolactinoma: galactorrhea, amenorrhea, infertility; tx cabergoline/bromocriptine
  • Acromegaly/Gigantism: ↑ IGF-1; diagnosis with glucose suppression test; tx surgery ± octreotide/pegvisomant
  • Mass effects: bitemporal hemianopsia

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Rapid review checklist (the night before)

• Know dopamine’s role: dopamine inhibits prolactin
• Prolactinoma symptoms = hypogonadism + galactorrhea
• First-line prolactinoma tx = dopamine agonist
• GH adenoma best marker = IGF-1
• Confirmation = oral glucose fails to suppress GH
• Acromegaly associations: DM, OSA, cardiomyopathy, colon polyps
• Macroadenoma = bitemporal hemianopsia