A 26-year-old woman has amenorrhea, galactorrhea, and a serum prolactin of 65 ng/mL. MRI shows a 9 mm pituitary lesion. A second patient has similar symptoms with prolactin of 320 ng/mL and a 14 mm sellar mass. Which statement correctly separates these two scenarios?

• A Both patients have prolactin-secreting adenomas requiring surgery
• B The second patient more likely has acromegaly with co-secreted prolactin
• C Prolactin levels cannot distinguish stalk effect from adenoma; both need dopamine agonist trial
• D Mild hyperprolactinemia with a small lesion suggests stalk effect, whereas prolactin above roughly 200 ng/mL with a macroadenoma indicates true lactotroph adenoma ✓

Explanation

Any mass compressing the pituitary stalk interrupts hypothalamic dopaminergic inhibition, producing modest prolactin elevation, usually below about 200 ng/mL. True lactotroph (prolactin) adenomas secrete autonomously and produce proportionally higher levels, often exceeding 200 ng/mL with macroadenomas. This quantitative distinction prevents mislabeling a nonfunctioning macroadenoma as a prolactinoma. Dopamine agonists shrink prolactinomas but do nothing for other adenoma types, so the distinction guides therapy.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

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Written and medically reviewed by the StethoPrep medical team.