Oil cyst (breast)

Oil cysts in breast imaging refer to benign breast lesions where an area of focal fat necrosis becomes walled off by fibrous tissue. 

  • Non-tender palpable lump
  • asymptomatic

Fat debris from ruptured lipocytes tends to conglomerate to form a macroscopic pool of oil surrounded by lipid-laden macrophages or foam cells - known as an oil cyst. The wall can then calcify. Most often this occurs secondary to trauma or surgery; however, this is not always necessary.

The aetiology of oil cysts is felt to be most often an end-form of liquefaction fat necrosis of the breast resulting from trauma or surgery. However, some oil cysts arise independently, without a prior history of trauma or surgery

Typically seen as a radiolucent rounded mass of fat density +/- wall calcification, which if present typically appears as eggshell calcification.  

On ultrasound, most oil cysts are hypo-echoic with smooth walls and show neither posterior acoustic enhancement or shadowing. A very small proportion can represent an intracystic mass.

Breast imaging and pathology
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Article information

rID: 15123
System: Breast
Section: Pathology
Tag: cases
Synonyms or Alternate Spellings:
  • Oil cysts
  • Mammary oil cysts
  • Mammary oil cyst
  • Oil cyst

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Cases and figures

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    Case 1
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    Case 2: large calcified oil cyst in left breast on CXR
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    Case 3
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    Case 4: on CT
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