Lactational (Puerperal): Most common; typically occurs 2–6 weeks postpartum as a progression from untreated or inadequately treated lactational mastitis.
Non-lactational: Less common; associated with smoking, DM, nipple piercing, inverted nipples, or trauma.
Etiology:
Staphylococcus aureus (most common, including MRSA).
Streptococcus pyogenes, Pseudomonas, anaerobes (more common in non-lactating/subareolar abscesses).
Pathogenesis: Nipple fissuring/abrasion → bacterial entry → milk stasis → mastitis → localized focal parenchymal necrosis and pus collection.
Clinical Features
Symptoms:
Unilateral, severe focal breast pain, swelling, and localized tenderness.
Systemic symptoms: Fever, chills, malaise, body aches.
Physical Exam:
Painful, tender, erythematous breast mass.
Fluctuance (pathognomonic sign distinguishing abscess from uncomplicated mastitis).
Localized warmth, edema, skin induration.
Reactive axillary lymphadenopathy.
Diagnosis
Initial & Diagnostic Test of Choice (Imaging): Targeted Breast Ultrasound (US).
Findings: Hypoechoic/anechoic fluid collection with posterior acoustic enhancement, internal debris/septa, and hypervascular border.
Role: Confirms abscess and differentiates from simple mastitis (diffuse skin thickening/edema without fluid collection).
Key Labs:
CBC (leukocytosis with left shift).
Gram stain & culture of aspirated fluid (guides Abx de-escalation).
Biopsy:
Core needle biopsy or skin punch biopsy indicated if patient is non-lactating, post-menopausal, recurrent, or non-healing despite treatment to rule out inflammatory breast carcinoma (IBC).
Differential Diagnostics
Lactational Mastitis:
Diff: Diffuse erythema and tenderness without fluctuance; US shows parenchymal edema without fluid collection.
Galactocele:
Diff: Retention cyst due to occluded lactiferous duct; non-erythematous, painless or mildly tender, afebrile, aspiration yields milky fluid.
Inflammatory Breast Carcinoma (IBC):
Diff: Rapidly progressive erythema, edema, and peau d’orange appearance; non-responsive to Abx; no fluid collection on US; punch biopsy reveals dermal lymphatic invasion by tumor cells.
Simple Breast Cyst / Fibrocystic Changes:
Diff: Fluid collection on US, but afebrile, non-erythematous, lacking systemic inflammatory signs.
Surgical Incision & Drainage (I&D): Indicated if large (> 5 cm), multiloculated, overlying skin ischemia/necrosis, or failed needle aspiration.
Empiric Antibiotic Therapy (10–14 days course):
Low MRSA Risk (Outpatient/Mild): Dicloxacillin or Cephalexin PO.
High MRSA Risk / Community-Acquired MRSA: Trimethoprim-sulfamethoxazole (TMP-SMX) or Clindamycin PO.
Note: Avoid TMP-SMX in nursing mothers with infants < 1 month or with hyperbilirubinemia.
Severe / Inpatient Sepsis: IV Vancomycin.
Lactation Management (High-Yield USMLE Concept):
Continue breastfeeding or pumping from BOTH breasts (including affected breast) every 2–3 hours to promote milk drainage and prevent stasis/re-accumulation.
Temporary cessation of breastfeeding on affected side (pump and dump) only if incision/wound directly interferes with latch or purulent discharge contacts infant’s mouth.
Symptomatic Support: NSAIDs/acetaminophen for pain/fever; warm compresses.
Complications
Recurrence or non-healing abscess (warrants biopsy for malignancy).
Mammary duct fistula (subareolar abscesses in smokers).