Introduction

Breast abscesses are a complication of infectious mastitis. They occur most commonly in breastfeeding women with mastitis, affecting an estimated 3-11 % of women in this group, but can also occur in non-lactating women and men. The infective organism is most commonly Staphylococcus aureus , and up to 50-60% of such cases have been reported to involve methicillin-resistant Staphylococcus aureus (MRSA). Aspiration with culture is both diagnostic (to guide antibiotic treatment), and therapeutic.

Epidemiology

  • Incidence: 125.00 cases per 100,000 person-years
  • Peak incidence: 30-40 years
Condition Relative
incidence
Breast abscess1
Breast cancer0.76
Breast fibroadenoma0.26
Fat necrosis of the breast0.03
<1 1-5 6+ 16+ 30+ 40+ 50+ 60+ 70+ 80+

Aetiology

Breast abscesses are an infective process, and a variety of microorganisms are implicated.

  • Infectious mastitis and subsequent breast abscess are usually caused by Staphylococcus aureus (32%), over half of which now typically are methicillin-resistant S. aureus (MRSA).
  • Other implicated microorganisms include coagulase-negative Staphylococcus, diphtheroids and Pseudomonas aeruginosa.
  • However, up to 40% of breast abscesses may be polymicrobial.
  • Non-lactational abscesses are more common among obese women, smokers, and those with diabetes.
  • Amongst non-lactating women, nipple piercings are associated with a higher risk of breast abscess, which can be associated with distinct microorganisms such as Group B Streptococcus and Mycobacterium.

Pathophysiology

Milk stasis in lactating women, secondary to breastfeeding technique or a blocked duct, can cause mastitis.
  • Mastitis, in turn, may become infectious mastitis following bacterial contamination from the skin, and a complication of this is a breast abscess
  • Abscess formation involves the body creating a capsule of granulomatous tissue around the developing infection to attempt to contain it.
  • Non-lactational breast abscesses may be caused by duct ectasia, which is a thickening and widening of the mild duct generally seen in women aged 45-55, and that can cause mastitis and subsequent infection.

Clinical features

Patients may present with systemic features of infection alongside localised breast symptoms. A full clinical history should be taken, including a neonatal and breastfeeding history if appropriate. A clinical examination including both breasts and axillary and cervical lymph nodes must be done, with a general examination including temperature, heart rate and respiratory rate to exclude sepsis.

Common signs:
  • Severely painful unilateral breast lump (77%)
  • Associated erythema and oedema
  • Fever and flu-like symptoms

Other, less common signs include:

Investigations

Blood tests to help assess severity of infection as well as imaging are required to work up patients with suspected breast abscesses.

  • Blood tests:
    • Full blood count
    • U&E
    • CRP
    • Blood cultures if clinically unwell/septic.
  • Consider pregnancy test if not a breast-feeding woman.
  • Imaging:
    • Breast ultrasound to characterise abscess.
    • Mammogram to rule out underlying breast lesion.
  • Microbiology
    • Culture of needle aspirate of abscess to inform antibiotic choice
    • Milk culture may be helpful

Differential diagnosis

The key differential diagnoses involve non-infectious benign breast diseases. Malignancy must be excluded.

  • Galactocele
    • Milk cyst in lactating women. Not usually accompanied by localised pain or systemic signs of infection.
  • Fibrocystic breasts
    • Typically multi-focal lumps with monthly pain around menses, improving with menstruation. Not accompanied by systemic illness. Distinguished on ultrasound.
  • Fibroadenoma
    • Benign breast tumours, distinguishable from breast abscess on ultrasound. No systemic illness.
  • Invasive breast cancer
    • Malignant breast lesions may present similarly, and are distinguished on mammogram and ultrasound with biopsy of the lesion to confirm pathology.
  • Fat necrosis
    • Usually secondary to breast trauma resulting in a firm round tender lump, usually without erythema. Biopsy confirms diagnosis.
  • Cellulitis
    • Skin infection that may present with painful, erythematous area of skin with associated signs of systemic infection.
  • TB mastitis.
    • A rare presentation of TB, often mimicking and possibly co-existing with breast abscess. Systemic features of TB including indicative history, and a positive Mantoux test.

Management

Key principles of management are drainage of pus in the abscess with appropriate antibiotic treatment.

1. Surgical management
  • First line management is needle aspiration of the abscesses under 5cm, under local anaesthetic and usually with ultrasound guidance. This may need to be repeated daily over a period of 5-7 days.
  • Larger abscesses, or those that do not resolve with needle aspiration, will need surgical incision and drainage with washout, or percutaneous drainage with indwelling catheter.

2. Adjuvant medical management
  • Aspiration must be accompanied by antibiotic treatment. If MRSA has been ruled out and the patient is systemically well then appropriate oral antibiotics may be used e.g. flucloxacillin or dicloxacillin.
  • In penicillin allergic patients, or if MRSA grown on culture aspirate, doxycycline or clindamycin are effective.
  • Systemically unwell patients may need intravenous antibiotics e.g. Vancomycin.

3. Breast emptying in lactational abscesses
  • Breast milk should continue to be expressed in the presence of a breast abscess as this provides symptomatic relief from breast engorgement.
  • If suckling is painful especially during the acute period, or following surgical intervention, then the mother should be encouraged to express manually or using a pump to avoid breast engorgement.