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