💧 Leaky Faucets Explained
Pathologic discharge is typically unilateral, spontaneous, and from a single duct.
| Cause | Discharge Type | Key Features / Histo |
|---|---|---|
| Intraductal Papilloma | Bloody/Serosanguineous | Benign papillary growth in a large duct. Fibrovascular core lined by epithelial & myoepithelial cells. |
| DCIS/Invasive Ca | Bloody/Serosanguineous | Malignant cells within duct, no myoepithelial layer. May have associated mass. |
| Mammary Duct Ectasia | Green/Brown, sticky | Periductal inflammation, plasma cells, duct dilation with lipid-laden macrophages. |
| Physiologic/Galactorrhea | Milky, bilateral | ↑ Prolactin. Requires bilateral, multi-duct expression. Check TSH, pregnancy test. |
🕵️ The Discharge Detective
- Initial Assessment: Differentiate physiologic vs. pathologic.
- Physiologic: Bilateral, multiductal, non-bloody (milky/yellow/green).
- Workup: Pregnancy test, TSH, prolactin.
- Causes: Galactorrhea (prolactinoma, hypothyroidism, drugs), pregnancy.
- Pathologic: Unilateral, uniductal, bloody, serosanguineous, or clear/watery.
- Causes: Intraductal papilloma, duct ectasia, malignancy (DCIS/IDC).
- Physiologic: Bilateral, multiductal, non-bloody (milky/yellow/green).
⭐ The most common cause of unilateral, bloody nipple discharge is a benign intraductal papilloma, not malignancy.
- Pathologic Discharge Workup Algorithm:
💧 Fixing the Flow
- Physiologic: Bilateral, multi-ductal, milky/yellow/green. Often expressible, not spontaneous. Causes: pregnancy, lactation, hyperprolactinemia, hypothyroidism.
- Pathologic: Unilateral, uni-ductal, spontaneous, bloody (papilloma, cancer), serosanguinous, or clear (cancer). Warrants full workup.
⭐ The most common cause of unilateral, bloody nipple discharge is a benign intraductal papilloma. However, malignancy must always be ruled out.

⚡ Biggest Takeaways
- Pathologic discharge is typically unilateral, uniductal, and spontaneous (bloody/serous); physiologic is often bilateral and multiductal.
- The most common cause of bloody nipple discharge is a benign intraductal papilloma.
- Always rule out malignancy, especially Ductal Carcinoma In Situ (DCIS) or invasive cancer.
- Initial workup for pathologic discharge includes mammography and ultrasound, particularly in women >30.
- For milky, bilateral discharge (galactorrhea), check prolactin and TSH levels.
- If imaging is negative but discharge remains suspicious, terminal duct excision is diagnostic.
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