A 48-year-old woman has bitemporal hemianopia from a 3 cm sellar mass. Serum prolactin is mildly elevated at 95 ng/mL (normal up to 25). After transsphenoidal resection, histology shows a nonfunctioning gonadotroph adenoma. What explains her mild hyperprolactinemia?

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

Explanation

Nonfunctioning pituitary macroadenomas commonly cause mild hyperprolactinemia through the stalk effect: the expanding mass compresses the infundibulum, cutting off hypothalamic dopamine delivery to lactotrophs and disinhibiting them. Stalk effect hyperprolactinemia typically stays below roughly 200 ng/mL, whereas true prolactin-secreting macroadenomas usually produce levels far higher, often above 250 ng/mL. Recognizing this distinction matters because a nonfunctioning adenoma will not shrink with cabergoline the way a prolactinoma does.

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

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Written and medically reviewed by the StethoPrep medical team.