Fat necrosis (breast)

Dr Jeremy Jones et al.

Fat necrosis within the breast is a pathological process that occurs when there is saponification of local fat. It is a benign inflammatory process and is becoming increasingly common with greater use of breast conserving surgery and mammoplasty procedures.

Most at risk are middle-aged women with pendulous breasts. The onset of fat necrosis can be considerably delayed, occurring 10 years or more after surgery 3.

At a microscopic level, the initial change is disruption of fat cells where vacuoles with the remnants of necrotic fat cells are formed. They then become surrounded by lipid-laden macrophages, multinucleated giant cells, and acute inflammatory cells. Fibrosis develops during the reparative phase peripherally enclosing an area of necrotic fat and cellular debris. Eventually, fibrosis may replace the area of degenerated fat with a scar, or loculated and degenerated fat may persist for years within a fibrotic scar.

Aetiology

When there is calcification within the cyst wall it is termed liponecrosis macrocystica calcificans.

Location

There is a predilection towards the subareolar and periareolar regions.

Mammography

Fat necrosis can have a very variable, sometimes alarming appearance on mammography and is often potentially confusing to the novice breast imager. Initially, it can be seen as an ill-defined and irregular, spiculated mass-like area. Associated calcification can be seen, which can mimic that of more malignant entities such as DCIS.

Note that fat necrosis of the breast can change with time with progressive calcification so comparison with previous imaging is essential. Also, the changes can often be seen and correlated with the position of surgical scarring on the breast itself (refer to the technologist sheet).

The calcification of fat necrosis is typically peripheral with a stippled curvilinear appearance creating the appearance of lucent "bubbles" in the breast parenchyma. Note the low density centres. Tumour formation is not a part of fat necrosis although it may be clinically palpable.

With time, it becomes more defined and well-circumscribed giving rise to an oil cyst. Oil cysts can have very fine curvilinear calcification of the walls. The centre of the lesion becomes increasingly homogenous with fat-density. The cyst wall calcify in ~ 5%. 

Breast ultrasound

Fat necrosis may be seen as a hypoechoic mass with well defined margins +/- mural nodule(s). The identification of the subtle wall nodularity in an oil cyst is a dead giveaway but takes effort and real time imaging. Ultrasound of fat necrosis should always be interpreted in the context of mammographic findings.

Aspiration of an oil cyst shows typically a milky, emulsified fat appearance. In the sample bottle the fat globules can be seen drifting on the cytology before they disperse. Typical appearance and immediately recognisable.

On ultrasound, the lesion may occasionally represent an intracystic carcinoma and mammographic correlation is recommended in these circumstances 1. The key to diagnosis is the history, the tech sheet and review of multiple cases.

Breast imaging and pathology
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Article Information

rID: 9025
System: Breast
Section: Pathology
Synonyms or Alternate Spellings:
  • Breast fat nacrosis
  • Traumatic fat necrosis of the breast
  • Fat necrosis (breast)

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Cases and Figures

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    Case 1: associated with scar (arrowed)
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    Case 2 : MRI T1 fat-sat
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    2012 MLO
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