Idiopathic granulomatous mastitis

Deputy Editor-in-Chief: Debra L. Zynger, M.D.
Mary Ann Gimenez Sanders, M.D, Ph.D.

Topic Completed: 1 February 2018

Minor changes: 6 May 2021

Copyright: 2003-2021,, Inc.

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

Mary Ann Gimenez Sanders, M.D, Ph.D.
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Cite this page: Gimenez Sanders MA. Idiopathic granulomatous mastitis. website. Accessed June 23rd, 2021.
Definition / general
  • Lobulocentric granulomatous inflammation
  • Diagnosis of exclusion (excluding other granulomatous conditions)
  • 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
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

Contributed by Nicolas Ajkay, M.D.
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IGLM with multiple
sinus tracts
opening onto skin
(tattoo blocked)

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IGLM with response
to corticosteroidsc
(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

Contributed by Mary Ann Gimenez Sanders, M.D., Ph.D.
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I&D specimen with IGLM and inflammation

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Lumpectomy with IGLM showing inflammation

Images hosted on other servers:

Nonnecrotizing granulomas with giant cells

Granulomatous inflammation centered on breast lobules

Cytology description
Negative stains
Differential diagnosis
Board review style 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 style answer #1
C. Multiple sinus tracts are seen opening out onto the skin.

In advanced cases of idiopathic granulomatous mastitis (IGLM), multiple sinus tracts opening onto the skin can occur. IGLM is not associated with squamous metaplasia, unlike SMOLD. By definition, IGLM has no known etiology. Known etiologies of granulomatous mastitis include Corynebacterium (a gram positive bacillus), also known as CGNM, and hyperprolactinemia. An AFB positive stain would confirm a mycobacterial infection as the cause for granulomatous mastitis and GMS stain demonstrating yeast and hyphae would confirm a fungal infection as the cause for granulomatous mastitis. It is important to rule out an infectious cause before diagnosing IGLM since corticosteroids are a common treatment for IGLM but are contraindicated for infections.

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Reference: Breast nonmalignant - Idiopathic granulomatous mastitis
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