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 abscess | 1 |
| Breast cancer | 0.76 |
| Breast fibroadenoma | 0.26 |
| Fat necrosis of the breast | 0.03 |
| <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:
Other, less common signs include:
Common signs:
- Severely painful unilateral breast lump (77%)
- Associated erythema and oedema
- Fever and flu-like symptoms
Other, less common signs include:
- Tender axillary lymphadenopathy
- Nipple discharge
- Breast fistula
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
2. Adjuvant medical management
3. Breast emptying in lactational abscesses
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.