Pituitary adenomas show up everywhere on USMLE because they’re high-yield, clinically “visual,” and testable from multiple angles: neuroanatomy, endocrinology, ophthalmology, and even pharmacology. If you can picture the sella turcica and what sits right above it, you can answer most questions in seconds.
The “SELLA” visual hack (draw it in 5 seconds)
Picture the pituitary as a tiny “SELLA” shop sitting in a bony saddle, with a big X-shaped sign hovering just above it.
- S = Sella turcica (where the tumor grows)
- E = Endocrine hypersecretion (functional tumors)
- L = Lateral cavernous sinus invasion (CN palsies)
- L = Loss of vision (bitemporal hemianopsia)
- A = Amenorrhea/galactorrhea (prolactinoma) / Acromegaly (GH)
One-liner: Pituitary adenoma = sellar mass that causes endocrine symptoms + mass effect, classically compressing the optic chiasm → bitemporal hemianopsia.
Quick diagram to keep in your head
Order from top to bottom:
Optic chiasm
⬇ (compression by pituitary macroadenoma)
Pituitary gland in sella turcica
⬅➡ (lateral spread) cavernous sinus (CN III, IV, V1, V2, VI)
Why bitemporal hemianopsia?
Compression of crossing nasal retinal fibers at the optic chiasm → loss of temporal visual fields bilaterally.
Microadenoma vs macroadenoma (USMLE loves cutoffs)
| Feature | Microadenoma | Macroadenoma |
|---|---|---|
| Size | < 10 mm | ≥ 10 mm |
| Classic presentation | Hormone hypersecretion (esp. prolactin) | Mass effect (vision loss, headache) ± hormonal changes |
| Visual field defects | Uncommon | Common (optic chiasm compression) |
Functional pituitary adenomas: the high-yield trio
1) Prolactinoma (most common)
Clue set: galactorrhea + amenorrhea/infertility (women), decreased libido/ED (men)
Mechanism to remember:
Dopamine inhibits prolactin. So dopamine agonists treat prolactinomas.
Treatment: Cabergoline (or bromocriptine)
USMLE pitfall: Primary hypothyroidism can raise prolactin via TRH.
- TRH ↑ → TSH ↑ and prolactin ↑
So check TSH in hyperprolactinemia workups.
2) Somatotroph adenoma (GH-secreting)
Clue set: acromegaly (adults) or gigantism (kids), sweating, enlarged hands/feet, prognathism, OSA, cardiomyopathy
Labs:
- IGF-1 is the best screening test (more stable than GH)
- Oral glucose normally suppresses GH; failure to suppress = acromegaly
Treatment: transsphenoidal surgery ± octreotide (somatostatin analog) ± pegvisomant (GH receptor antagonist)
3) Corticotroph adenoma (ACTH-secreting)
Clue set: Cushing disease features (central obesity, proximal muscle weakness, HTN, glucose intolerance, purple striae)
Testable distinction:
- High-dose dexamethasone suppresses ACTH in pituitary Cushing (Cushing disease)
- Ectopic ACTH typically does not suppress
Nonfunctional adenomas: mass effect + hypopituitarism
Nonfunctional pituitary adenomas often present when they’re big enough to cause compression.
High-yield mass effects:
- Headache
- Bitemporal hemianopsia
- Hypopituitarism from compression of normal pituitary tissue
Hormone loss tends to go in an order (common teaching):
GH → gonadotropins (LH/FSH) → TSH → ACTH (posterior pituitary usually spared)
Cavernous sinus invasion = cranial nerve palsies
A lateral-growing pituitary macroadenoma can invade the cavernous sinus.
Cavernous sinus contents to remember:
- CN III, IV, V1, V2, VI
- Internal carotid artery
- Sympathetic fibers
Classic deficits:
- CN III palsy: ptosis, “down and out,” mydriasis
- CN VI palsy: impaired abduction (lateral rectus)
- Facial sensory loss (V1/V2)
Pituitary apoplexy: the emergency presentation
Think: sudden hemorrhage into a pituitary adenoma.
Presentation:
- Sudden severe headache
- Visual changes/ophthalmoplegia
- Possible altered mental status
- Acute hypopituitarism (can precipitate adrenal crisis)
Management (board-style):
- Immediate glucocorticoids (treat possible acute adrenal insufficiency)
- Neurosurgical evaluation (often urgent decompression)
Imaging + approach (what Step questions expect)
- MRI with contrast: best for pituitary adenoma
- Visual field testing if macroadenoma suspected
- Endocrine labs targeted to symptoms (prolactin, IGF-1, cortisol/ACTH, TSH/free T4, LH/FSH)
Pro tip: A mildly elevated prolactin can be due to stalk effect (dopamine can’t reach pituitary well). A very high prolactin level points more toward true prolactinoma.
Ultra-high-yield recap (memorize this)
- Macroadenoma → optic chiasm compression → bitemporal hemianopsia
- Prolactinoma → galactorrhea + amenorrhea/infertility; treat with cabergoline
- GH adenoma → acromegaly; screen with IGF-1; glucose fails to suppress GH
- ACTH adenoma → Cushing disease; high-dose dexamethasone suppresses
- Pituitary apoplexy → thunderclap headache + vision changes; give steroids now