A 30-year-old woman has amenorrhea and galactorrhea. MRI shows a 6 mm pituitary lesion. Serum prolactin is 320 ng/mL. The most likely pathological diagnosis and expected IHC finding are:
- A Prolactinoma (lactotroph adenoma) — strongly prolactin-positive on IHC ✓
- B Null cell adenoma — no hormone immunoreactivity on IHC
- C Somatotroph adenoma — GH positive causing acromegaly
- D Craniopharyngioma — squamous cells with Rathke cleft cyst
Correct answer: A. Prolactinoma (lactotroph adenoma) — strongly prolactin-positive on IHC
Explanation
Prolactinoma (lactotroph adenoma) is the most common functioning pituitary adenoma; microadenomas typically present in women with hyperprolactinemia causing amenorrhea-galactorrhea. IHC shows diffuse prolactin positivity (densely or sparsely granulated). Null cell adenomas have no hormone staining; somatotroph adenomas cause acromegaly; craniopharyngioma is a suprasellar tumor, not an intrasellar parenchymal adenoma.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.