A female patient with galactorrhea and amenorrhea; MRI shows a pituitary microadenoma. What is the most likely diagnosis?

• A. Prolactinoma (prolactin-secreting pituitary adenoma).
• B. Nonfunctioning pituitary adenoma.
• C. Growth hormone secreting pituitary adenoma.
• D. Cushing disease.

Answer: (A)

High prolactin levels disrupt the normal reproductive hormonal axis by inhibiting GnRH from the hypothalamus. When GnRH is suppressed, LH and FSH fall, leading to anovulation and amenorrhea. Prolactin also directly causes galactorrhea by stimulating breast tissue. A pituitary microadenoma that secretes prolactin fits this pattern: a small, estrogen-unregulated rise in prolactin produces both galactorrhea and menstrual disturbances, and MRI can reveal a small pituitary lesion consistent with a prolactin-secreting tumor.

Other pituitary tumors would present with different hormonal or mass-effect features (for example, growth hormone–secreting tumors causing signs of excess IGF-1 and acromegaly, or Cushing disease with cortisol-related symptoms). A nonfunctioning adenoma could cause mild prolactin elevation via stalk effect but typically doesn’t cause prominent galactorrhea. Therefore, the presentation most strongly points to a prolactin-secreting pituitary adenoma.