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Breast

Inflammatory / infectious

Fat necrosis

Authors: Elizabeth Abels, M.D., Jing He, M.D.

Editorial Board Member: Julie M. Jorns, M.D.

Editor-in-Chief: Debra L. Zynger, M.D.

Last author update: 1 November 2022

Last staff update: 9 June 2023

Copyright: 2002-2024, PathologyOutlines.com, Inc.

PubMed Search: Fat necrosis breast pathology

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Table of Contents

Cite this page: Abels E, He J. Fat necrosis. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/breastfatnecrosis.html. Accessed April 20th, 2024.

Definition / general

Nonneoplastic inflammatory breast lesion characterized by necrotic adipose tissue with foamy histiocytes, chronic inflammatory cells and multinucleated giant cells

Essential features

Nonneoplastic inflammatory reaction that is commonly secondary to adipose tissue injury
May simulate carcinoma both clinically and radiologically
There are different radiographical and histological stages which vary based on time from inciting event

ICD coding

ICD-10: N64.1 - fat necrosis of breast
ICD-11: GB23.2 - fat necrosis of breast

Epidemiology

0.6% of breast excisions
Age range: 37 - 68 years (mean age: ~50 years) (Breast 2006;15:313)
Most described in perimenopausal women after trauma, surgery or biopsy

Sites

Any part of the breast may be affected
After trauma, typically occurs at site of injury and is commonly detected in periareolar and subareolar region; it is often superficial in location since these sites are most vulnerable to trauma (Lipids Health Dis 2019;18:158)
In patients with no history of trauma, lesion is most often seen in upper outer quadrant of breast

Pathophysiology

Many cases are due to previous biopsy procedures (such as fine needle aspiration or needle core biopsy), surgical procedure or radiation therapy (Plast Reconstr Surg 2014;134:1202)
May result from incidental trauma

Etiology

Trauma:
- Blunt trauma to breast (e.g., seat belt injury after motor vehicle accident) (J Plast Reconstr Aesthet Surg 2015;68:382)
Iatrogenic injury:
- Fine needle aspiration, core needle biopsy, mastectomy or lumpectomy of breast, autologous fat injection, reduction mammoplasty, breast implants (Breast Cancer 2019;26:125)
Radiation therapy:
- Due to postradiation vascular damage with subsequent ischemia, including external beam, MammoSite, iridium implantation, intraoperative radiation
Other rare causes:
- Anticoagulant treatment (warfarin [Coumadin]), polyarteritis nodosa, Weber-Christian disease, granulomatous angiopanniculitis, lupus mastitis, injection of methylene blue dye
Unknown cause in ~50% of patients

Clinical features

Typically present with a painless superficial solitary mass which may mimic cancer, especially in patients who have undergone breast conserving surgery and radiation therapy (Lipids Health Dis 2019;18:139)
Firm and relatively circumscribed on palpation, may span 2 cm in diameter (average)
Occasionally can be associated with skin changes: bruising and tenderness, tethering or dimpling of the overlying skin if the lesion is superficially located, nipple retraction

Diagnosis

Palpation of breast mass, radiographical findings and correlation with clinical history of trauma or breast procedures (Lipids Health Dis 2019;18:139)
Core needle biopsy is frequently performed if there are masses or calcifications
Tissue diagnosis needs to correlate with imaging findings and must be used to distinguish from fat necrosis next to another lesion

Radiology description

Many cases can be identified by radiographic appearance (e.g., forming mammographic masses or mammographic calcifications)
Manifestations on mammography, ultrasonography and MRI depend upon its stage of evolution; features can be variable and may be indistinguishable from carcinoma (Radiol Res Pract 2015:613139)
Time from inciting event may be useful in correlating radiographic findings (Br J Radiol 2018;91:20180213)
Mammography usually reveals ill defined irregular mass with or without calcifications or focal asymmetries around central area of necrotic adipose tissue
May contain punctate, irregular or coarse pleomorphic calcifications
Sonography demonstrates a discrete mass which may be well circumscribed or ill defined
- Sonographic appearance is variable and is usually associated with distortion of the parenchymal architecture
Less frequently, the lesion may appear as a lipid (oil) cyst which consists of a circumscribed, round or oval radiolucent oil filled cyst that is partly calcified
- Oil cysts typically show posterior acoustic shadowing by sonography
Eggshell calcifications are late findings with characteristic appearance around central area of necrotic adipose tissue
MRI demonstrates a wide spectrum of findings
- Necrotic fat usually shows low signal intensity on T1 weighted MRI
- Fibrosis may be seen as architectural distortion

Radiology images

Images hosted on other servers:

Contraction
and
microcalcification

Fat necrosis within surgical site

Prognostic factors

Should resolve or regress over time (Br J Radiol 2018;91:20180213)
Degenerated fat may persist for years within a fibrotic scar

Case reports

40 year old woman with breast pain for 3 months (Pan Afr Med J 2016;25:235)
63 year old woman was found to have a left breast mass after quadrantectomy and radiation (Magn Reson Imaging 2004;22:285)
66 year old woman with palpable breast masses one month after a car accident (Eur J Ultrasound 2000;11:213)
71 year old woman with painful bilateral breast masses and overlying skin changes (Dermatol Online J 2018;24:13030)
Case series of fat necrosis after breast conserving oncoplastic surgery (Breast Cancer 2019;26:125)

Treatment

Biopsy the lesion to confirm the diagnosis if clinical / radiological features can not distinguish from cancer
Follow up with imaging and clinical examination to detect occult carcinoma that might be masked by coexisting fat necrosis
Surgical excision is usually not necessary after the diagnosis has been established, only for painful or aesthetically undesirable lesions (StatPearls: Breast Fat Necrosis [Accessed 1 May 2020])

Clinical images

Images hosted on other servers:

Skin and fat necrosis due to methylene blue

Gross description

Varies based on time from injury
- Early lesion has the appearance of hemorrhage in indurated fat (Radiol Res Pract 2015:613139)
  - Cut surface of the lesion has a variegated, yellow-gray appearance with focally reddish color
- After several weeks, it appears as a firm yellow-gray nodule / mass with a demarcated border
  - Mass may retract surrounding parenchyma, cystic degeneration may develop in the center, showing a cavity containing oily fluid secondary to necrotic fat with calcification in the cystic walls
- At a later stage, the lesion may show a dense scar that may appear like a mass

Gross images

Contributed by Elizabeth Abels, M.D.

Fat necrosis within biopsy site

Frozen section description

Frozen sections are difficult to obtain due to high fat content of specimen

Microscopic (histologic) description

Histiocytes are relatively uniform in size with round nuclei, fine intracytoplasmic vacuoles and no indentation of the nucleus
Varies based on time from injury
- Early stage:
  - Necrosis of adipocytes (fine vacuolization, diminished size and dropout)
  - Focal hemorrhage in fat (AJR Am J Roentgenol 2009;192:815)
  - Cystic degeneration may result in cavity with or without calcifications in cyst walls
  - Formation of demarcated distinct yellow-gray and focally reddish mass over several weeks
- Intermediate stage:
  - Mixed inflammatory cell infiltrate of histiocytes, lymphocytes, plasma cells, sometimes with eosinophils
  - Lipid laden foamy histiocytes and multinucleated foreign body type giant cells are due to phagocytosis of necrotic adipocytes
  - Hemosiderin deposition
  - Early fibrosis with hypercellular areas of fibroblastic proliferation
- Late stage:
  - Varying degrees of fibrosis and calcifications may remain for years
  - Fibrosis contract into a scar and may result in irregular mass
  - Loculated necrotic fat within a cyst surrounded by dense fibrous tissue (oil cyst) with dense calcification in the walls of cysts (eggshell calcifications)
  - Reactive squamous metaplasia may develop in the epithelium of ducts and lobules in the area of lesion

Microscopic (histologic) images

Contributed by Jing He, M.D.

Disruption of adipocytes

Mixed inflammation

Mixed inflammatory cells

Hemorrhage and hemosiderin

Hemosiderin and giant cells

Multinucleated giant cells

Lipid laden histiocytes and hemorrhage

Lipid laden histiocytes

Mass formation

Necrotic adipocytes

Cystic degeneration

Early fibrosis

Oil cyst

Late stage fibrosis

Eggshell calcifications

CD68

AE1 / AE3

Cytology description

Characterized by lipid laden histiocytes (lipophages), multinucleated giant cells and degenerating adipocytes (AJR Am J Roentgenol 2009;192:815)
Lipid laden macrophages demonstrate abundant foamy cytoplasm with variably sized clear lipid vacuoles and small, bland nuclei
Histiocytes are relatively uniform in size with round nuclei, fine intracytoplasmic vacuoles and no indentation of the nucleus
Degenerating adipocytes are characterized by aggregates of adipocytes that have lost their nuclei and have finely granular cytoplasm instead of the clear cytoplasm that is characteristic of lipid
Reactive and reparative changes involving fibroblasts and histiocytes can result in cells with large pleomorphic nuclei and prominent nucleoli
Background may show scattered inflammatory cells, hemosiderin laden macrophages, globules and acellular lipid
Scant clusters of ductal epithelial cells are usually cytologically bland but may exhibit cytologic atypia with pleomorphic nuclei and prominent nucleoli

Cytology images

Images hosted on other servers:

Stages of fat necrosis

Positive stains

CD68

Negative stains

AE1 / AE3, CAM 5.2, Congo red

Videos

Breast traumatic fat necrosis

Breast inflammatory conditions

Sample pathology report

Breast, right, retroareolar, core biopsy:
- Fat necrosis

Differential diagnosis

Breast carcinoma:
- May have abundant foamy cytoplasm and small bland nuclei that can mimic histiocytes
- Usually demonstrates more nuclear atypia
- Cytokeratin+, CD68-
Lipomatous neoplasm:
- Vacuolated cytoplasm and hyperchromatic, indented or often scalloped nuclei
- S100+, CD34+
Granular cell tumor:
- Infiltrating tumor cells with abundant eosinophilic granular cytoplasm
- Minimal to no inflammatory infiltrate
- S100+, CD68 variable
Amyloidosis (Pathol Res Pract 2019;215:152699):
- Can present as mass or calcifications with amyloid surrounding adipocytes
- Usually associated with systemic amyloidosis and hematologic disorder such as plasmacytoma
- No chronic inflammatory cell infiltrate
- Amyloid deposits within blood vessel walls and causes thickening of basement membranes and vascular walls
- Congo red apple green birefringence under polarized microscopy
Erdheim-Chester disease:
- Infrequent xanthomatous form of non Langerhans cell histiocytosis
- Usually synchronous nonmammary subcutaneous nodules, osseous and orbital lesions
- Infiltration of foamy histiocytes, Touton type giant cells, plasma cells and epithelioid granuloma
- CD68+, factor XIIIa (strong)+, S100 variable, CD1a-

Board review style question #1

Continue routine surveillance for this patient
Negative CD68 and positive AE1 / AE3 are characteristic of this lesion
The patient has recurrent breast carcinoma
The patient requires surgical excision of this lesion followed by chemotherapy

Board review style answer #1

A. Continue routine surveillance for this patient. Fat necrosis of the breast is a possible sequela of breast tissue trauma or surgical procedure. This patient likely developed fat necrosis after her initial resection and radiation therapy. When the diagnosis is unclear from radiology, biopsy is necessary to rule out cancer. The biopsy section shows foamy lipid laden histiocytes, mixed inflammatory cells infiltrate and disruption of adipocytes, associated with microcalcification. Positive CD68 and negative AE1 / AE3 can help to distinguish fat necrosis from recurrent carcinoma of breast. Fat necrosis is a nonneoplastic inflammatory process and usually surgical treatment is not required.

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Reference: Fat necrosis of breast

Board review style question #2

The cyst will often become infected and require surgical drainage
The lesion will be replaced by varying degrees of fibrosis
The lesion will eventually progress to invasive carcinoma if left untreated
The lesion will grow and compress surrounding tissue

Board review style answer #2

B. The lesion will be replaced by varying degrees of fibrosis. Fat necrosis has three stages of evolution. The first stage is characterized by disruption of adipocytes following an inciting event. This can lead to local cyst formation with or without calcifications. In the intermediate stage, inflammatory cells phagocytose the necrotic adipocytes and fibroblasts proliferate. Eventually the fibroblasts replace the necrotic areas with varying degrees of fibrosis. Fat necrosis is a nonneoplastic inflammatory lesion that usually resolve or regress over time.

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Reference: Fat necrosis of breast

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