Definition/General

Introduction:
-Fat necrosis is a benign inflammatory process in the breast that results from injury to the adipose tissue
-It can mimic malignancy clinically and mammographically.
Origin:
-It is caused by trauma to the breast, including surgery, radiation, or accidental injury
-In many cases, the patient does not recall a specific traumatic event.
Classification:
-It is a benign, non-proliferative breast lesion.
Epidemiology:
-It is a common finding, especially in women with large breasts who are more prone to trauma.

Clinical Features

Presentation:
-Can present as a painless, firm, irregular, palpable mass
-Skin retraction or dimpling can occur, further mimicking carcinoma.
Symptoms:
-A painless breast lump is the most common symptom
-It can also be tender.
Risk Factors: History of breast trauma, surgery, or radiation.
Screening: Mammography can show a spiculated mass, architectural distortion, or calcifications (classically coarse or eggshell-like), which can be suspicious for malignancy.

Master Fat Necrosis Pathology with RxDx

Access 100+ pathology videos and expert guidance with the RxDx app

Gross Description

Appearance:
-An ill-defined, firm, nodular lesion
-The cut surface can be yellow-gray and may contain chalky white deposits (saponification) or cystic spaces filled with oily fluid (oil cysts).
Characteristics: The lesion can be hemorrhagic in the early stages.
Size Location: Size is variable.
Multifocality: Can be multifocal if the trauma was extensive.

Microscopic Description

Histological Features:
-The microscopic features vary with the age of the lesion
-Early lesions show hemorrhage and an inflammatory infiltrate of neutrophils and macrophages
-Later lesions are characterized by anucleated adipocytes, foamy macrophages (lipophages), multinucleated giant cells, and lymphocytes
-Fibrosis and calcification are seen in late stages.
Cellular Characteristics: The key cells are the foamy macrophages (lipophages) that have phagocytosed lipid.
Architectural Patterns: The process is centered on necrotic fat lobules.
Grading Criteria: This is a benign lesion.

Immunohistochemistry

Positive Markers: Not typically required for diagnosis.
Negative Markers: Not typically required for diagnosis.
Diagnostic Utility: IHC is not used for diagnosis.
Molecular Subtypes: Molecular subtyping is not relevant for this benign condition.

Molecular/Genetic

Genetic Mutations: This is a benign condition and is not associated with specific genetic mutations.
Molecular Markers: No specific molecular markers are routinely used for diagnosis.
Prognostic Significance: Fat necrosis is a benign condition and is not associated with an increased risk of breast cancer.
Therapeutic Targets:
-No treatment is required
-Biopsy is often performed to exclude malignancy.

Differential Diagnosis

Similar Entities:
-Invasive carcinoma
-Granulomatous mastitis.
Distinguishing Features:
-Invasive carcinoma is composed of malignant epithelial cells
-Granulomatous mastitis is centered on lobules and has well-formed granulomas.
Diagnostic Challenges:
-The main challenge is the clinical and mammographic mimicry of carcinoma
-The presence of foamy macrophages and anucleated adipocytes on biopsy is diagnostic.
Rare Variants: There are no specific rare variants.

Sample Pathology Report

Template Format

Sample Pathology Report

Complete Report: This is an example of how the final pathology report should be structured for this condition.

Specimen Information

[specimen type], measuring [size] cm in greatest dimension

Diagnosis

[diagnosis name]

Classification

Classification: [classification system] [grade/type]

Histological Features

Shows [architectural pattern] with [nuclear features] and [mitotic activity]

Size and Extent

Size: [X] cm, extent: [local/regional/metastatic]

Margins

Margins are [involved/uninvolved] with closest margin [X] mm

Lymphovascular Invasion

Lymphovascular invasion: [present/absent]

Lymph Node Status

Lymph nodes: [X] positive out of [X] examined

Special Studies

IHC: [marker]: [result]

Molecular: [test]: [result]

[other study]: [result]

Final Diagnosis

Final diagnosis: [complete diagnosis]