01OverviewDefinition, clinical context and the essential points that orientate the chapter.
An abscess forms when infection and inflammation cause liquefaction within breast tissue and the body walls off pus. Antibiotics alone often cannot sterilise an established cavity, making drainage the defining treatment. Lactational abscesses often follow mastitis and are commonly peripheral, whereas non-lactational collections cluster around subareolar ducts and may recur in association with smoking, diabetes or fistula.
Ultrasound turns an imprecise tender mass into an anatomical plan: it shows whether fluid is drainable, whether septations demand multiple passes or a catheter, and whether a suspicious solid component remains. Aspiration preserves breastfeeding and breast contour better than a large incision in many cases. Operative drainage remains necessary when minimally invasive source control fails, skin is compromised or anatomy is unsuitable. Every pathway ends with proof that the cavity and underlying abnormality have resolved.
Key points
- A breast abscess is a localised collection of infected fluid, usually presenting with focal pain, swelling, erythema and fever after lactational or non-lactational mastitis.
- Ultrasound confirms fluid, measures depth and loculation, distinguishes phlegmon from drainable pus and guides aspiration away from vulnerable skin and implants.
- Needle aspiration is commonly used for accessible collections and may need repetition; catheter or operative drainage is selected for large, multiloculated, recurrent or poorly accessible abscesses.
- Send aspirated pus for culture and susceptibility, then refine antibiotics to clinical severity, lactation, allergy, renal function, prior organisms and local resistance guidance.
- Breastfeeding or milk expression can usually continue in lactational abscess with positioning advice that avoids infant contact with purulent drainage or an unsafe wound.
- Failure to resolve, recurrent same-site disease, a residual mass or atypical non-lactational presentation requires repeat imaging and tissue assessment for fistula, granulomatous disease or malignancy.
02AetiologyUnderlying causes, associations and risk factors, with why each one matters.
Lactational bacterial spread
Milk stasis, inflamed lobules and nipple disruption permit bacterial proliferation and progression from mastitis into a localised cavity.
Non-lactational duct infection
Periductal disease, smoking, diabetes, immune compromise and skin infection can seed central or peripheral non-lactational collections.
03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.
- 1Tissue liquefaction
Neutrophils and bacterial enzymes destroy local tissue, producing viscous pus within an inflamed breast compartment cavity.
- 2Cavity encapsulation
Granulation tissue and oedema wall off infection, limiting antibiotic penetration and creating the need for mechanical drainage.
- 3Pressure and skin compromise
Expanding fluid raises tissue pressure, causing severe pain, thinning skin and eventual spontaneous rupture or fistula.
04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.
A focal exquisitely tender swelling with warmth, erythema and fluctuation suggests abscess, but deep collections may feel firm and require ultrasound rather than bedside certainty.
Fever and tachycardia are common; hypotension, confusion, severe dehydration or rapidly spreading change indicates need for hospital resuscitation and intravenous treatment.
Recent mastitis, nipple trauma and impaired milk removal support a lactational source. Feeding history helps plan drainage and maintain supply without creating greater oversupply.
Repeated periareolar abscess, sinus, persistent mass, unusual organisms or absent response suggests diseased ducts, immune compromise, granulomatous mastitis or malignant mimic.
05InvestigationsWhat to request, why it matters and how to interpret it.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
Targeted ultrasoundFirst step - Why
- Confirm, map and measure drainable fluid and identify loculation or solid tissue.
- Interpretation and limitations
- A complex avascular fluid cavity with surrounding hyperaemia supports abscess. Phlegmon may not yield pus, while a vascular mural component requires tissue diagnosis.
- 02
Image-guided aspiration - Why
- Provide source control and a microbiological specimen with minimal tissue injury.
- Interpretation and limitations
- Record volume, appearance and residual cavity. Repeat aspiration can be appropriate if the collection shrinks; failure to improve prompts catheter or surgical review.
- 03
Pus culture and susceptibility - Why
- Identify organisms in recurrent, severe or treatment-resistant infection.
- Interpretation and limitations
- Use a deep aspirate rather than surface swab where possible. Prior antibiotics can sterilise culture, so a negative result does not erase imaging-confirmed pus.
- 04
Core biopsy after acute control - Why
- Diagnose persistent solid or inflammatory tissue not explained by infection.
- Interpretation and limitations
- Target residual mass or abnormal skin after oedema subsides. Inflammatory histology must remain concordant and microbiological stains or cultures may be needed.
06Differential diagnosisRealistic alternatives and the features that help distinguish them.
Inflammatory phlegmon
Diffuse inflammatory tissue has no organised fluid cavity and is managed medically with imaging follow-up rather than futile drainage.
Galactocele
A milk-retention cyst may be painless and show fat-fluid features, although secondary infection can transform it into an abscess.
Inflammatory breast cancer
Diffuse oedema and erythema without a resolving collection, especially outside lactation, requires urgent imaging and tissue diagnosis.
07ManagementImmediate care, first-line treatment, alternatives and escalation.
01Ultrasound-guided drainage pathwayTreat an accessible lactational abscessFirst stepUltrasound shows a unilocular 3 cm peripheral collection in a stable breastfeeding adult with a healthy term infant, preserved renal function, no relevant beta-lactam allergy and no known MRSA risk.+
- 1Assess sepsis risk, allergy and feeding, then explain aspiration, possible repetition, bleeding, pain and the small risk of milk fistula.
- 2Before puncture, use aseptic preparation and local infiltration anaesthesia after checking the agent, dose ceiling, allergies and patient risks. Confirm adequate anaesthesia, then aspirate under ultrasound, send pus for culture and record the immediate reduction and residual volume.
- 3Use the NHS Highland stable-adult abscess example: flucloxacillin 500 mg orally four times daily for 7–10 days, alongside drainage, with culture-led revision. Explain empty-stomach administration and the product precautions below; continue comfortable breastfeeding or expression. Sepsis, spreading cellulitis, threatened skin, diabetes, immunosuppression or suspected MRSA requires the corresponding urgent specialist pathway.
- 4EscalationReview clinically and by ultrasound within the local interval, repeating aspiration if improving but residual fluid remains and escalating if it does not shrink.
02Escalation pathwayChoose catheter or operative source controlEscalationA large multiloculated collection reaccumulates after two technically adequate aspirations and the overlying skin is thinning.+
- 1Re-image the full extent and assess whether locules communicate, whether a catheter can remain safely and whether skin viability is threatened.
- 2Obtain senior breast-surgical and radiological input for catheter drainage or operative incision, avoiding delay from another low-yield isolated aspiration.
- 3DefinitiveReview culture, antibiotic penetration and host factors such as diabetes or immune suppression while definitive drainage proceeds.
- 4Plan wound care and lactation support and confirm that no residual solid component remains after the cavity collapses.
03Non-resolving mass pathwayLook beyond infectionPain and fever resolve after drainage, but a firm irregular area remains at the abscess margin six weeks later.+
- 1Repeat breast and nodal examination and obtain targeted imaging after inflammatory oedema has settled.
- 2Compare the residual area with the original cavity and identify whether it represents scar, diseased duct or a separate solid lesion.
- 3Obtain image-guided core from suspicious persistent tissue and consider inflammatory cancer, granulomatous mastitis and unusual infection.
- 4Track histology and microbiology to multidisciplinary concordance before discharging a patient with an atypical or recurrent abscess.
Key medicines and prescribing safety2 treatments · regimens, roles and cautions+
Plain lidocaine 1% for local infiltration
Aguettant lidocaine 10 mg/mL pre-filled syringe is a checked plain product for local intradermal/subcutaneous infiltration before drainage. Select the smallest effective dose for the procedure. Its usual adult infiltration total is 3–5 mg/kg, with a generally recommended maximum of 200 mg (20 mL of 1%); the ceiling is not a target dose. Use a lower patient-specific dose when indicated.Exclude allergy to lidocaine, amide local anaesthetics or excipients. Cardiac or hepatic insufficiency may require reduction by up to half; renal impairment, frailty, conduction disease, epilepsy and anticoagulation require individual review. Count other local anaesthetics and check antiarrhythmics and clearance-reducing interactions. Avoid intravascular injection; infected tissue can reduce effect while increasing absorption. Have resuscitation facilities available. Stop injection and summon help for perioral numbness, tinnitus, neurological change, seizure or cardiovascular disturbance; manage suspected local-anaesthetic systemic toxicity promptly. This is not an IVRA or adrenaline-mixture regimen. Recommended local doses permit continued breastfeeding.
Flucloxacillin after lactational abscess drainage
For the specified stable adult without relevant allergy or resistant-organism risk, NHS Highland recommends 500 mg orally four times daily for 7–10 days for breast abscess. The selected capsules are taken one hour before or two hours after food with a full glass of water (250 mL), without lying down immediately afterwards.Avoid beta-lactam/product hypersensitivity and previous flucloxacillin-associated hepatic injury. Assess liver disease; CrCl below 10 mL/min needs an individual lower-dose/longer-interval decision. Check warfarin/INR, methotrexate, probenecid and voriconazole interactions. If paracetamol is also used, severe renal impairment, sepsis or malnutrition warrants review for high anion gap acidosis risk and appropriate monitoring. Observe a healthy term infant for diarrhoea, thrush, rash or poor feeding. This example is not a prescription for MRSA, penicillin allergy, severe illness or recurrent smoking-related central disease.
08ComplicationsImportant consequences, why they occur and why they matter clinically.
Sepsis
Bacterial infection may enter the bloodstream and cause organ dysfunction, requiring urgent hospital resuscitation and intravenous treatment.
Skin necrosis or fistula
Untreated pressure and inflammation can destroy overlying skin or establish a chronic tract to a diseased duct.
Recurrence and scarring
Incomplete drainage, resistant organisms or persistent duct disease can cause repeated collections, breast distortion and feeding difficulty.
09Monitoring and follow-upTreatment response, safety checks and longer-term review.
- Measure erythema, pain, temperature and cavity dimensions after drainage so failure of source control is detected before skin breakdown.
- Check aspirate culture and susceptibility and revise antimicrobial therapy with allergy, lactation and organ function documented.
- For lactating patients, review infant attachment, milk transfer, supply and wound position while avoiding aggressive pumping of an already overproducing breast.
- Confirm complete cavity resolution and reassess any residual solid tissue; symptomatic improvement alone does not prove diagnostic closure.
10Special situationsVariants, exceptions and circumstances that change the usual approach.
Phlegmon is not free pus
Inflamed oedematous tissue can look mass-like without a drainable cavity. Repeated blind needling adds trauma when ultrasound shows no fluid target.
Aspiration may be serial
Need for a second aspiration does not equal treatment failure if cavity volume and symptoms are falling; trend and anatomy guide escalation.
Incision affects feeding
A surgical wound near the nipple or infant’s mouth complicates direct feeding. Lactation and wound teams can find a safe position or temporary expression plan.
Resolution proves the model
A genuine abscess should shrink after adequate drainage and therapy. Persistent tissue challenges the infection-only explanation and deserves biopsy.
11Common pitfallsFrequent interpretation and management errors.
- 01
Prescribing repeated antibiotics without draining ultrasound-confirmed pus leaves the central source untreated.
- 02
Performing blind incision before ultrasound can miss a deep cavity and create unnecessary breast scarring.
- 03
Stopping breastfeeding automatically can worsen stasis and is rarely required solely because an abscess was drained.
- 04
Discharging after fever settles without reassessing a residual mass can miss granulomatous disease or carcinoma.