34. Mastitis and breast abscess

1. Definition

• Mastitis → inflammation of the breast tissue, infective or non-infective
• Breast abscess → localised collection of pus in the breast

2. Epidemiology

• Lactational mastitis → up to 1 in 10 breastfeeding women, mostly in the first 3 months
• Abscess → small proportion of lactational mastitis

3. Aetiology and risk factors

Lactational

• Organisms → Staphylococcus aureus most common (including methicillin-resistant S. aureus, MRSA), streptococci
• Entry through a cracked nipple during breastfeeding
• Milk stasis → poor attachment, missed feeds, engorgement, tight clothing

Non-lactational

• Periductal mastitis → smoking (strongest risk factor), diabetes; mixed aerobic and anaerobic flora (anaerobes common in smokers)
• Duct ectasia → peri- and postmenopausal women; creamy or green nipple discharge
• Nipple piercing
• Idiopathic granulomatous mastitis → young parous women, oral contraceptive use; associated with Corynebacterium
• Rare → tuberculosis, actinomycosis, infected sebaceous cyst

Neonatal

• Breast bud infection in the first weeks of life → S. aureus

4. Pathogenesis

Lactational

1. Milk stasis
2. Bacteria enter through the nipple into the ducts
3. Cellulitis of the breast → mastitis
4. Untreated or late treatment → localised suppuration → abscess, often multiloculated

Periductal

1. Smoking damages subareolar ducts
2. Ductal inflammation and secondary infection
3. Subareolar abscess
4. Rupture or drainage at the areolar margin → mammary duct fistula
5. Repeated cycles → scarring, nipple retraction

5. Classification

• Lactational (puerperal)
• Non-lactational:
  • Periductal mastitis, subareolar abscess
  • Peripheral non-lactational abscess
  • Granulomatous mastitis
  • Chronic → tuberculosis, actinomycosis
• Neonatal
• By stage → serous (cellulitis), infiltrative, abscess

6. Clinical picture

Symptoms

• Painful, swollen, red area of the breast
• Fever, rigors, malaise → lactational
• Recurrent subareolar pain and seropurulent discharge → periductal

Signs

• Tender, warm, erythematous wedge-shaped area
• Abscess → fluctuant tender mass (fluctuation may be absent in deep abscess)
• Brawny oedema of the overlying skin
• Tender axillary lymph nodes
• Periductal → subareolar mass, slit-like nipple retraction, fistula at the areolar margin

7. Diagnosis

• Clinical in most

Laboratory

• Full blood count → leucocytosis
• Culture of milk or pus → guides antibiotics; review result and screen for MRSA at 48 h

Imaging

• Ultrasound → confirms abscess, size, loculation; guides aspiration
• Mammography → avoid in the acute painful phase; non-lactating women over 35 years after the infection settles
• Core biopsy:
  • Not settling after treatment or residual mass → exclude inflammatory carcinoma
  • Granulomatous mastitis → non-necrotising granulomas

8. Differential diagnosis

• Inflammatory breast carcinoma → diffuse redness, peau d'orange, no fever, no response to antibiotics
• Breast engorgement
• Galactocele → milk cyst; sterile creamy fluid on aspiration
• Infected cyst
• Fat necrosis

9. Treatment

Conservative

• Mastitis:
  • Continue breastfeeding or expressing → empties the breast; safe for the baby
  • Lactational → flucloxacillin 500 mg orally four times daily (1 g IV if unwell) or co-amoxiclav
  • Penicillin allergy → cefalexin with caution, clarithromycin or clindamycin; cover MRSA if risk
  • Non-lactational → co-amoxiclav, or a macrolide plus metronidazole
  • Analgesia, cold compresses, supportive bra
  • No improvement in 48 h → ultrasound for abscess
• Abscess:
  • Ultrasound-guided needle aspiration under local anaesthetic → first-line; repeated daily or on alternate days until no pus
  • No ultrasound and patient unwell → bedside aspiration
  • Antibiotics with aspiration
  • Periductal → antibiotics against anaerobes (co-amoxiclav, or flucloxacillin plus metronidazole)
  • Stop smoking
• Granulomatous mastitis → steroids first; observation, antibiotics against Corynebacterium (doxycycline), methotrexate; avoid surgery

Surgical

• Incision and drainage:
  • Failure of aspiration
  • Large, multiloculated abscess
  • Pointing abscess, thin or necrotic overlying skin → mini-incision over the abscess
  • Circumareolar or radial incision, break down loculi, wound left open to drain
• Recurrent periductal mastitis or fistula → excision of the major duct complex (Hadfield's operation) or fistulectomy, after the acute infection settles

Follow-up

• Re-examine 8–12 weeks after treatment → cancer can mimic infection
• Residual mass → triple assessment
• Comparison with cancer → see the article "Mastitis or breast cancer"

10. Complications

• Recurrence → periductal mastitis, smokers
• Mammary duct fistula
• Nipple retraction, deformity
• Milk fistula after drainage in lactation
• Sepsis
• Delayed diagnosis of carcinoma