Inflammatory Breast Lesions

Updated: Aug 16, 2018


  • Acute mastitis +/- Abscess Formation

  • Chronic (Lymphocytic) Mastitis/Diabetic Mastopathy

  • Granulomatous Inflammation

  • Fat Necrosis

Acute Mastitis +/- Abscess formation

General Information

  • Classical signs of inflammation (heat, redness, swelling, painful)

  • Staph most common cause

  • Inc PMNs (neutrophils) with intraductal and periductal inflammation


  • Due to a fissure in the skin from breastfeeding that allows for infection of underlying breast.

  • Often due to Staphylococcus aureus or streptococci (Strep often produces diffuse cellulitis)

Clinical Picture

  • Usually mom comes in a month after starting breastfeeding with an irritated, inflamed breast.

  • Can form a firm mass in breast (DDx: CANCER!)

  • Typically unilateral (affecting the side used for breastfeeding)

  • If untreated with antibiotics, infection can spread or an abscess can form. (see abscess for more details)


  • Lots of neutrophils

  • Abscess formation= organization with fibrous scar formation around area of infection/neutrophils/pus etc

Differential Diagnosis:


Chronic Lymphocytic Mastitis (Diabetic Mastopathy)


  • Often presents as a discrete mass in young patients with Type 1 Diabetes

  • Similar histologic features can be seen in patients with other autoimmune diseases

  • Ex: Hashimoto's disease; or even in individuals without autoimmune diseases or in men


  • Breast tissue with dense keloid-like stromal fibrosis (paucicellular, often glassy in appearance)

  • Dense lymphocytic infiltrates surrounding lobules, ducts and blood vessels

  • Lymphocytes are predominantly B-cells (NOTE: there is NO inc risk for lymphoma)

  • Epithelioid stromal cells (myofibroblasts) with enlarged nuclei and small nucleoli

(Idiopathic) Granulomatous inflammation

General Information:

  • Most granulomatous inflammatory lesions of the breast are idiopathic.

  • Often clinically presents as a mass lesion in young females with a history of recent pregnancy.

Histologic findings:

  • Granulomatous inflammation admixed with neutrophils

  • A few granulomas show central neutrophilic infiltrate (microabscess)

  • Caseous necrosis is NOT seen

DDx: Must exclude other causes of granulomatous inflammation (TB, sarcoid, fungal infection etc)

Fat Necrosis


  • Phagocytosis of necrotic adipose cells

  • Most common cause is trauma (MVC etc.)

  • Can be seen with duct ectasia that has ruptured (may have apocrine metaplasia present)

Clinical picture

  • Trauma to breast then patient has a localized, firm area with eventual scarring & calcifications.

Histologic Findings

Histologic Findings:

  • Consists of necrotic adipocytes, fibrosis and inflammation

  • Irregular steatocytes with loss of peripheral nuclei

  • Pink amorphous necrotic material/debris

  • Inflammatory cells

  • Foamy (lipid-laden) macrophages

  • +/- Foreign body giant cells

  • Neutrophils/lymphocytes/plasma cells

  • BEWARE: Reactive fibroblasts and reactive endothelial cells can look ugly and can be confused with carcinoma!!

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