Breast - nonmalignant
Inflammatory / infectious
Granulomatous mastitis (idiopathic)

Author: Mary Ann Gimenez Sanders, M.D., Ph.D. (see Authors page)

Revised: 26 February 2018, last major update February 2018

Copyright: (c) 2003-2018,, Inc.

PubMed Search: Breast [title] granulomatous mastitis (idiopathic)

Cite this page: Sanders, M. Granulomatous mastitis (idiopathic). website. Accessed March 19th, 2018.
Definition / general
  • Lobulocentric granulomatous inflammation
  • Diagnosis of exclusion (excluding other granulomatous conditions)
  • Also called (idiopathic) granulomatous lobular mastitis (GLM)
  • Rare
  • Most common in parous women, childbearing age
  • Usually occurs 2 years or more after pregnancy
  • Median age in the 30s
  • No relation to smoking
  • Idiopathic / diagnosis of exclusion: special stains and cultures should be negative
  • Growing evidence showing association between GLM and cystic neutrophilic granulomatous mastitis which is due to Corynebacterium (Pathology 2017;49:405, Am J Surg Pathol 2015;39:1440)
  • Other proposed causes: autoimmune response, hyperprolactinemia (Breast J 2016;22:224)
Clinical features
  • Palpable breast mass
  • May have related skin changes
  • Presentation can be similar to breast cancer
  • Occurs anywhere in the breast except the nipple
  • May result in sinus tract out onto skin
  • May have multiple sinus tracts in advanced cases
  • May recur
Case reports
Clinical images

Images hosted on PathOut server:

Images contributed by Nicolas Ajkay, M.D.
Missing Image

GLM with multiple sinus
tracts opening out onto
the skin (tattoo blocked)
Missing Image

GLM with response
to corticosteroids
(tattoo blocked)

Images hosted on other servers:

Appearance of second lump postbiopsy

Firm mass with multiple sinuses

Gross description
  • Firm, hard, faintly nodular mass
Microscopic (histologic) description
  • Granulomatous inflammation centered on lobules with lymphocytes, plasma cells, epithelioid histiocytes, multinucleated giant cells and neutrophils
  • May have neutrophils forming microabscesses and surrounding empty microcysts; overlapping features with cystic neutrophilic granulomatous mastitis
  • Usually no necrosis
Microscopic (histologic) images

Images hosted on PathOut server:

Images contributed by Mary Ann Gimenez Sanders, M.D., Ph.D.
Missing Image Missing Image Missing Image

I&D specimen with GLM showing inflammation

Missing Image Missing Image

Lumpectomy with GLM showing inflammation

Images hosted on other servers:

Various images

Nonnecrotizing granulomas with giant cells

Granulomatous inflammation centered on breast lobules

Cytology description
Negative stains
Differential diagnosis
  • Cystic Neutrophilic Granulomatous Mastitis (CNGM): GLM due to Corynebacterium
    • Occurs in parous women, same as idiopathic GLM
    • Granulomas with neutrophils and cystic spaces containing gram positive bacilli
    • Difficult to culture (Am J Clin Pathol 2011;136:424)
  • Other infections with granulomas: mycobacteria (Cases J 2008;1:273), fungi, cat scratch disease (Arch Pathol Lab Med 1989;113:473), Brucella (Acta Cytol 2009;53:667)
  • Wegener granulomatosis: necrotizing vasculitis is present
  • Sarcoidosis: well formed granulomas that are not confined to the lobules
  • Squamous Metaplasia of Lactiferous Ducts (SMOLD): ducts with squamous metaplasia
    • Multinucleated giant cells associated with keratin debris
    • Occurs in the nipple
    • Only one sinus tract at the areolar edge, if present
    • Associated with smoking
Board review question #1
    Of the following clinical or pathologic descriptions, which would be consistent with a diagnosis of idiopathic granulomatous lobular mastitis?

  1. AFB stain is positive.
  2. Gram positive bacilli are seen in microcysts within a granuloma.
  3. Multiple sinus tracts are seen opening out onto the skin.
  4. Patient has a pituitary adenoma.
  5. Squamous metaplasia is present.
Board review answer #1
C. Multiple sinus tracts are seen opening out onto the skin.

In advanced cases of GLM, multiple sinus tracts opening onto the skin can occur. GLM is not associated with squamous metaplasia unlike SMOLD. By definition, idiopathic GLM has no known etiology. Reported cases where etiology of GLM is known include GLM caused by Corynebacterium (a gram positive bacillus), also known as CGNM and GLM caused by hyperprolactinemia. An AFB positive stain would confirm a mycobacterial infection as the cause for granulomatous mastitis. It is important to rule out an infectious cause before diagnosing idiopathic GLM since corticosteroids is a common treatment.