01OverviewDefinition, clinical context and the essential points that orientate the chapter.
Granulomatous mastitis describes granulomatous inflammation centred on breast lobules. The idiopathic form often occurs within several years of pregnancy, but its cause remains incompletely understood and Corynebacterium species can be associated with a cystic neutrophilic pattern. The condition can mimic bacterial abscess and inflammatory breast cancer, with irregular masses, erythema, peau d’orange, ulcers and sinuses.
A safe diagnosis requires representative core tissue and purposeful infection exclusion. Histological granulomas are a pattern, not an aetiology: caseation, organisms, foreign material and malignant cells must be sought according to context. Treatment varies because disease can resolve spontaneously, relapse, or cause major tissue destruction. Drainage treats collections; antibiotics treat bacteria; immunosuppression treats selected sterile inflammation only after infection is addressed. Extensive surgery during active inflammation can produce poor healing and deformity.
Key points
- Granulomatous mastitis is a lobulocentric inflammatory breast disorder that can produce painful masses, sterile or infected abscesses, skin ulceration and draining sinuses.
- Idiopathic granulomatous mastitis is a diagnosis of exclusion; pregnancy-related history and Corynebacterium association are relevant, but tuberculosis, fungi, foreign body and carcinoma must be considered.
- Ultrasound maps collections and sinus tracts, while image-guided core biopsy provides architecture needed to show granulomas and exclude invasive malignancy.
- Send fresh tissue or pus for appropriate bacterial, mycobacterial and fungal studies before immunosuppression when epidemiology or histology supports those possibilities.
- Drain symptomatic collections in a tissue-sparing manner; ordinary antibiotics are useful only for demonstrated or clinically suspected bacterial infection, not for sterile inflammation alone.
- Observation, corticosteroids, steroid-sparing therapy and surgery are selected by specialist multidisciplinary assessment; recurrence and treatment toxicity require an explicit monitoring plan.
02AetiologyUnderlying causes, associations and risk factors, with why each one matters.
Idiopathic lobular inflammation
Immune reaction to secreted material outside damaged lobules is proposed, often in reproductive years after pregnancy, but no single cause is established.
Specific granulomatous causes
Corynebacterium, mycobacteria, fungi, foreign material and systemic inflammatory disease can produce similar histology and must be considered before idiopathic classification.
03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.
- 1Lobular disruption
Damage to lobular epithelium releases lipid and protein secretions into stroma, recruiting macrophages and multinucleated giant cells.
- 2Neutrophilic collections
Acute inflammation around damaged lobules creates microabscesses that may coalesce, track through tissue and reach the skin.
- 3Fibrosis and sinus formation
Chronic granulomas and repeated drainage produce collagen, tethering and epithelialised tracts that sustain discharge and mimic malignancy.
04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.
A painful irregular mass with erythema and oedema can involve several quadrants. Multiple small collections or sinus tracks are more suggestive than one simple abscess but are not diagnostic.
Many patients present during reproductive years after pregnancy or lactation. This association modifies probability but should not end infection and cancer assessment.
Corynebacterium-associated disease may show lipid vacuoles rimmed by neutrophils and granulomas; special culture conditions and communication with microbiology can improve detection.
Flares, new collections and sinus drainage may occur over months. Response and toxicity matter because repeated procedures and immunosuppression can cause substantial harm.
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
- Map masses, collections, oedema and sinus tracts and select aspiration or core targets.
- Interpretation and limitations
- Irregular hypoechoic areas and multiple collections overlap with infection and cancer. Ultrasound defines anatomy but cannot establish idiopathic disease.
- 02
Image-guided core biopsy - Why
- Demonstrate lobulocentric granulomatous inflammation and exclude malignancy.
- Interpretation and limitations
- Pathology should assess necrosis, giant cells, neutrophilic vacuoles, foreign material and malignant epithelium; limited superficial samples may miss the key pattern.
- 03
Tissue and fluid microbiology - Why
- Exclude bacterial, mycobacterial and fungal causes before immunosuppression.
- Interpretation and limitations
- For recurrent abscess or granulomatous mastitis, the Barts work-up requests routine bacterial culture, mycobacterial culture and histology alongside targeted Corynebacterium kroppenstedtii PCR when relevant. Send tissue or pus for microbiology in a sterile container and allocate histology separately with the laboratory. Fungal stains/culture or molecular studies follow exposure and pathological clues. Prior antibiotics and difficult organism growth can limit sensitivity, so negative results need clinical and tissue correlation.
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Cause-directed systemic assessment - Why
- Identify tuberculosis exposure, sarcoidosis, immune disease or drug and foreign-body causes.
- Interpretation and limitations
- Chest imaging, TB testing or other tests follow clinical clues; a broad unstructured autoimmune panel does not replace breast tissue diagnosis.
06Differential diagnosisRealistic alternatives and the features that help distinguish them.
Bacterial or tuberculous mastitis
Pyogenic organisms, Corynebacterium and mycobacteria require dedicated cultures or molecular tests because immunosuppression would be hazardous.
Inflammatory breast cancer
Diffuse dermal oedema and mass can be identical clinically; representative breast and sometimes skin tissue is needed to exclude malignancy.
Foreign-body reaction
Suture, silicone, injected material or fat injury can provoke giant-cell inflammation and is identified through history, imaging and pathology.
07ManagementImmediate care, first-line treatment, alternatives and escalation.
01Diagnostic pathwayProve the pattern and exclude causesFirst stepA non-lactating patient has recurrent culture-negative breast collections and an irregular inflammatory mass despite two antibiotic courses.+
- 1Reassess for sepsis and inflammatory cancer, map collections with ultrasound and obtain mammography appropriate to age and tissue tolerance.
- 2Core the solid inflammatory margin and aspirate fluid, alerting pathology and microbiology to possible granulomatous disease before specimens are processed.
- 3Request bacterial, mycobacterial and fungal studies according to histology and exposure and avoid corticosteroids until important infection is reasonably excluded.
- 4Discuss the integrated tissue, imaging and microbiology result at the breast multidisciplinary meeting and state whether idiopathic disease is truly supported.
02Steroid-consideration pathwayUse immunosuppression with safeguardsCore-proven idiopathic granulomatous mastitis remains painful and extensive after collections are drained and infection studies are negative.+
- 1Measure disease extent, baseline glucose, blood pressure, infection risk and pregnancy intentions and document the symptoms that justify systemic treatment.
- 2Agree corticosteroid or steroid-sparing treatment with breast and relevant medical specialists, using a patient-specific regimen rather than an invented universal dose.
- 3Monitor clinical mass, skin, new fluid, metabolic toxicity and opportunistic infection and taper only under the responsible prescriber’s plan.
- 4Re-biopsy or re-culture a new atypical focus or deterioration rather than assuming every flare is sterile recurrence.
03Persistent-sinus pathwayMinimise destructive surgerySeveral sinuses drain intermittently after repeated wide incisions, with no undrained large cavity and benign concordant core histology.+
- 1Map active tracts and confirm no drainable collection or missed malignancy remains.
- 2Provide wound care, analgesia and medical inflammatory control while allowing active tissue inflammation to settle where clinically safe.
- 3Reserve surgery for limited refractory disease, necrotic tissue or reconstruction after stabilisation, explaining risk of further fistula and contour loss.
- 4Review healing, recurrence and psychosocial burden over a defined interval and coordinate one lead team to avoid contradictory treatment cycles.
08ComplicationsImportant consequences, why they occur and why they matter clinically.
Recurrent abscess and sinus
Relapsing microcollections can rupture through skin and create chronic draining tracts, infection and prolonged wound-care needs.
Treatment toxicity
Corticosteroids and steroid-sparing drugs can cause metabolic, infectious, hepatic, haematological or reproductive harms requiring specialist monitoring.
Breast distortion
Fibrosis, tissue loss and repeated surgery can cause asymmetry, nipple displacement and lasting functional and psychological burden.
09Monitoring and follow-upTreatment response, safety checks and longer-term review.
- Map mass dimensions, erythema, ulcers, sinuses and ultrasound collections at baseline so response is more than a pain score.
- Before and during immunosuppression, monitor infection symptoms, glucose, blood pressure and agent-specific blood tests under the specialist protocol.
- Repeat culture and imaging for a new collection; prior sterile fluid does not guarantee that later tissue is uninfected.
- Document complete or partial remission and a relapse route because recurrent inflammation may emerge after treatment taper or apparent wound closure.
10Special situationsVariants, exceptions and circumstances that change the usual approach.
Granuloma is a reaction pattern
Tuberculosis, fungi, foreign material, sarcoid-like disease and idiopathic inflammation can all create granulomas. Histology alone does not supply the cause.
Specimen handling determines yield
Tissue placed entirely in formalin cannot undergo ordinary culture. Plan fresh microbiology material before biopsy when infection is a meaningful possibility.
Antibiotics need a target
Repeated broad antibiotics do not treat sterile granulomatous inflammation, but Corynebacterium or secondary infection may require culture-informed therapy.
Surgery can amplify morbidity
Wide excision through actively inflamed tissue may heal poorly and distort the breast. It is not a routine shortcut around careful diagnosis and medical management.
11Common pitfallsFrequent interpretation and management errors.
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Starting corticosteroids before excluding tuberculosis, fungal or bacterial disease can disseminate or mask infection.
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Calling granulomas idiopathic without checking for necrosis, organisms and foreign material mistakes a pattern for a diagnosis.
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Repeating wide incision for every small sterile collection can produce more sinuses and substantial breast deformity.
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Assuming persistent peau d’orange is benign inflammation without concordant core biopsy can delay inflammatory-cancer diagnosis.