## Diagnosis: Prolactinoma ### Clinical Presentation **Key Point:** Prolactinomas are the most common functional pituitary adenomas and typically present with amenorrhea, galactorrhea, and visual symptoms due to mass effect. ### Imaging Features - **Homogeneous enhancement** on contrast MRI - **Sellar/suprasellar location** with optic chiasm compression from below - **No cystic component** (unlike craniopharyngiomas) - Size varies: microadenomas (<10 mm) vs. macroadenomas (>10 mm) ### Laboratory Findings **High-Yield:** Serum prolactin >200 ng/mL strongly suggests prolactinoma; levels >2000 ng/mL are virtually diagnostic. The degree of elevation correlates with tumor size. ### Pathophysiology Prolactinomas arise from lactotroph cells and are typically D2 dopamine receptor-positive. Dopamine inhibits prolactin secretion, making dopamine agonists (bromocriptine, cabergoline) first-line therapy. ### Differential Imaging Considerations | Feature | Prolactinoma | Craniopharyngioma | Non-functional Adenoma | Meningioma | |---------|--------------|-------------------|----------------------|------------| | Enhancement | Homogeneous | Heterogeneous, cystic | Variable | Homogeneous, dural tail | | Cystic component | Rare | Common (90%) | Uncommon | Rare | | Prolactin level | Markedly elevated (>200) | Normal | Normal | Normal | | Compression direction | From below | From above | Variable | Dural attachment | | Age of onset | Reproductive years | Childhood/young adult | Any age | Middle-aged/elderly | **Clinical Pearl:** The combination of markedly elevated prolactin (>2000 ng/mL) + homogeneous sellar mass + optic chiasm compression from below is pathognomonic for prolactinoma. 
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