Inflammatory breast lesions
- Lesion
Breast inflammation ranges from the infection of breastfeeding to lesions that feel and look like cancer, which is why many end up biopsied.
What it is
Inflammatory breast disorders are uncommon outside lactation, and several of them mimic carcinoma by forming hard masses, retracting the skin or calcifying. Acute mastitis is a bacterial infection of the lactating breast. Squamous metaplasia of lactiferous ducts, strongly tied to smoking, plugs the ducts with keratin and causes recurrent subareolar abscesses. Duct ectasia, fat necrosis, lymphocytic mastopathy and granulomatous mastitis complete the group.
Structure
- Acute mastitis: neutrophils filling ducts and lobules, sometimes with abscess cavities.
- Squamous metaplasia: keratinizing squamous epithelium extending deep into nipple ducts, keratin debris, and a granulomatous reaction to spilled keratin.
- Duct ectasia: dilated ducts with inspissated secretions and foamy macrophages, surrounded by plasma cells, lymphocytes and fibrosis.
- Fat necrosis: necrotic fat cells, foamy macrophages, multinucleated giant cells, haemosiderin, then fibrosis and calcification.
- Lymphocytic mastopathy: dense keloid-like collagen with lymphocytes around ducts, lobules and vessels.
- Cystic neutrophilic granulomatous mastitis: granulomas around clear vacuoles that contain gram-positive rods (Corynebacterium).
Step by step
- During lactation, a cracked nipple lets skin bacteria into the milk ducts, where stasis helps them grow.
- In smokers, the duct lining undergoes squamous metaplasia; keratin plugs block the duct.
- Blocked ducts dilate and rupture; their contents escape into the stroma.
- Keratin, lipid or milk products provoke intense inflammation, granulomas and abscesses.
- Healing leaves fibrosis that retracts the nipple or skin and can feel like a tumour.
Inflammatory breast lesions at a glance
| Lesion | Typical patient | Key histology | Why it matters |
|---|---|---|---|
| Acute mastitis and abscess | Breastfeeding woman | Neutrophils, abscess | Needs antibiotics or drainage |
| Squamous metaplasia of lactiferous ducts | Smoker | Keratinizing metaplasia, keratin granulomas | Recurrent subareolar abscess and fistula |
| Duct ectasia | Older parous woman | Dilated ducts, plasma cells | Mimics cancer (retraction, mass) |
| Fat necrosis | After trauma or surgery | Foamy macrophages, giant cells, calcification | Mimics cancer on imaging |
| Lymphocytic mastopathy | Type 1 diabetes, autoimmune thyroid disease | Keloid-like stroma, lymphocytes | Hard mass, often recurrent |
| Granulomatous mastitis | Parous women; systemic disease | Granulomas, sometimes microbes | Exclude tuberculosis and fungi |
Clinical notes
- Lactational mastitis is treated with continued milk drainage and antibiotics; breastfeeding usually continues.
- Inflammatory carcinoma can look like mastitis: a red, swollen breast outside lactation that does not respond to antibiotics needs a biopsy.
- In Colombia, tuberculous mastitis should be considered in a granulomatous breast lesion.
Test yourself
Think of the answer, then tap the question to see it.
Which organism most often causes lactational breast abscess?
Staphylococcus aureus.
What is the strongest risk factor for squamous metaplasia of lactiferous ducts?
Smoking.
Why is fat necrosis clinically important?
It forms a firm mass with calcifications and skin retraction that mimics carcinoma on examination and imaging.
Elsewhere in DurgiPedia
Connections
Microorganisms2
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Acute Mastitis (StatPearls (NCBI Bookshelf), 2026); Breast Abscess (StatPearls (NCBI Bookshelf), 2026).
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Representative model, for educational purposes only.