Inflammatory / infectious

Idiopathic granulomatous mastitis

Editorial Board Member: Julie M. Jorns, M.D.
Deputy Editor-in-Chief: Gary Tozbikian, M.D.
Jonathan Marotti, M.D.

Last author update: 11 August 2021
Last staff update: 16 December 2021

Copyright: 2003-2024,, Inc.

PubMed Search: Idiopathic granulomatous mastitis[TI] breast pathology

Jonathan Marotti, M.D.
Page views in 2023: 28,811
Page views in 2024 to date: 8,970
Cite this page: Marotti J. Idiopathic granulomatous mastitis. website. Accessed April 14th, 2024.
Definition / general
  • Lobulocentric granulomatous inflammation
  • Diagnosis of exclusion (excluding other causes of granulomatous inflammation)
Essential features
  • Rare, benign inflammatory process affecting women of childbearing age
  • Clinical symptoms and radiologic findings concerning for breast cancer
  • Reported association with pregnancy, lactation, oral contraceptive pill use, hyperprolactinemia, autoimmunity
  • Lobulocentric granulomatous inflammation
  • Diagnosis of exclusion
  • Idiopathic granulomatous mastitis
  • Lobular granulomatous mastitis
ICD coding
  • ICD-10: N61.2 - granulomatous mastitis
  • ICD-11: GB21 - inflammatory disorders of breast
  • Rare
  • Most common in parous women, childbearing age
  • Frequent in postpartum and breastfeeding women
  • Median age in the 30s
  • Breast, most often unilateral, rarely bilateral
  • Unknown
  • Unknown
  • Proposed causes or associations: pregnancy, lactation, oral contraceptive pill use, hyperprolactinemia, autoimmunity, infection
Clinical features
  • Mimics breast cancer, including inflammatory breast cancer (Breast J 2019;25:1245)
  • Palpable breast mass
  • Breast pain
  • Abscess formation with fistula tract formation
  • Nipple retraction
  • Peau d'orange
  • Rare lymphadenopathy
  • Breast core biopsy or surgical excision with histologic examination
  • Microbiology studies to exclude infection
  • Serologic markers to exclude autoimmune processes
  • Endocrine studies
Radiology description
Radiology images

Images hosted on other servers:

Mammogram; focal asymmetry

Ultrasound; hypoechoic tubular extensions

MRI; enhancing retroareolar mass

Prognostic factors
  • Self limiting in approximately 50% of patients (Am J Surg 2015;210:258)
  • Can persist or recur, prompting treatment
Case reports
Clinical images

Contributed by Nicolas Ajkay, M.D.
Missing Image

IGLM with multiple
sinus tracts
opening onto skin

Missing Image

IGLM with response
to corticosteroids

Images hosted on other servers:

Appearance of second lump postbiopsy

Firm mass with multiple sinuses

Gross description
  • Gray-tan firm mass
  • Size variable; average 5 - 6 cm
  • Ill defined margins
  • Subtle nodularity
Microscopic (histologic) description
  • Lobulocentric granulomatous inflammation (Pathology 2004;36:254)
  • Granulomas often contain neutrophils
  • Neutrophils can create microabscesses; overlapping features with cystic neutrophilic granulomatous mastitis
  • Multinucleated giant cells, lymphocytes, plasma cells and eosinophils within and around lobules
  • Extensive inflammation might obliterate lobulocentric distribution
  • Caseous necrosis not present
  • Schauman and asteroid bodies not common
Microscopic (histologic) images

Contributed by Jonathan Marotti, M.D. and Mary Ann Gimenez Sanders, M.D., Ph.D.
Missing Image Missing Image

Lobulocentric inflammation

Missing Image

Multinucleated giant cells

Missing Image

Nonnecrotizing granulomas

Missing Image

Lobulocentric inflammation

Missing Image Missing Image

Granulomas and multinucleated giant cells

Cytology description
Positive stains
  • CD68: positive in histiocytes
Negative stains
  • Gram stain for gram positive bacilli (Corynebacterium)
  • Acid fast stain for mycobacteria
  • GMS or PAS stains for fungi
  • IgG4 in plasma cells for IgG4 related sclerosing mastitis
Sample pathology report
  • Left breast, needle core biopsy:
    • Breast tissue with lobulocentric granulomatous inflammation (see comment)
    • Comment: Sections show a lobulocentric mastitis with histiocytes, granulomas, neutrophils and lymphocytes. The histologic findings are nonspecific but the main differential diagnosis includes idiopathic granulomatous mastitis, cystic neutrophilic granulomatous mastitis (typically caused by Corynebacterium), other infection, sarcoidosis and reaction to foreign material, among others. Given the lobulocentric nature of the granulomatous inflammation and lack of currently identifiable microorganisms, idiopathic granulomatous mastitis is favored. However, clinical and microbiologic correlation is required. Special stains for bacteria, acid fast bacilli and fungi are negative. Foreign material is not identified. There is no evidence of malignancy in this sample.
Differential diagnosis
Board review style question #1

A 33 year old woman presents with a painful breast lump concerning for breast cancer. A core biopsy is performed. Which histologic finding is most characteristic of idiopathic granulomatous mastitis?

  1. Keratin debris with associated foreign body inflammatory response
  2. Large necrotizing granulomas
  3. Lobulocentric granulomatous inflammation
  4. Microcysts with gram positive bacilli
  5. Well formed granulomas within interlobular stroma
Board review style answer #1
C. Lobulocentric granulomatous inflammation. Although not specific, the most characteristic histologic finding of idiopathic granulomatous mastitis is granulomatous inflammation centered on lobules (lobulocentric inflammation). Idiopathic granulomatous mastitis can have overlapping histologic features with cystic neutrophilic granulomatous mastitis (CNGM); however, microcysts with gram positive bacilli (Corynebacterium) are identified in CNGM. Keratin debris with an associated foreign body inflammatory response is usually seen in squamous metaplasia of lactiferous ducts (SMOLD). Large necrotizing granulomas are more typical of an infectious processes, such as mycobacterial infection. The presence of well formed granulomas within the interlobular stroma suggests sarcoidosis.

Comment here

Reference: Idiopathic granulomatous mastitis
Back to top
Image 01 Image 02