A 40-year-old woman with a large nonfunctioning pituitary macroadenoma has serum prolactin of 85 ng/mL (normal up to 25). She has no galactorrhea. Which mechanism best explains this mild prolactin elevation?

• A Autonomous secretion of prolactin by the adenoma
• B Compression of the pituitary stalk interrupting dopaminergic inhibition ✓
• C Ectopic secretion of GnRH by the tumor
• D Renal failure reducing prolactin clearance

Explanation

Any mass expanding the sella can compress the infundibular stalk, cutting off hypothalamic dopamine from reaching lactotrophs, causing disinhibited prolactin release called the stalk effect. Levels typically stay below about 200 ng/mL, whereas true prolactinomas usually exceed 200 ng/mL in macroadenomas. This distinction matters because stalk effect needs surgery of the primary lesion, not dopamine agonist therapy.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.