Fat Necrosis of the Breast

The mammographic and sonographic appearance of fat necrosis depends on the degree of fibrosis. The mammographic appearance is more specific than sonography. Mammographic presentations of fat necrosis include the following:

• Fat cyst: Minimal fibrosis. Radiolucent mass with thin wall. Linear and curvilinear calcifications develop early and central calcifications can be seen later. If there is more fibrosis the wall may be thick, irregular, spiculated, or ill-defined. Fat cysts may contain fat–fluid levels, serous–hemorrhagic contents, or spherical densities. Collapsed oil cysts may also be seen.
• Focal asymmetries: A fat cyst whose center has been replaced by reparative fibrotic reaction may appear as a focal asymmetric density.
• Spiculated mass: A fat cyst whose center has been replaced by reparative fibrotic reaction may appear as a spiculated mass.
• Coarse calcifications: May be smooth and round or curvilinear.
• Microcalcifications: More worrisome appearance of calcifications, including branching, rodlike, or angular, can also be seen.

The sonographic appearance is varied, ranging from a solid mass to an anechoic mass with posterior enhancement with margins ranging from well circumscribed to indistinct to spiculated. A specific sonographic appearance of fat necrosis is a mass with echogenic internal bands that shift in orientation with changes in patient position. The most common presentation of fat necrosis is a hyperechoic subcutaneous mass.

On MRI fat necrosis may be indistinguishable from malignancy and can mimic tumor recurrence after breast conservation therapy. The degree of enhancement on MRI depends on the degree of inflammatory reaction.

References

Taboada JL, Stephens TW, Krishnamurthy S, Brandt KR, Whitman GJ. The many faces of fat necrosis in the breast. AJR Am J Roentgenol. 2009 Mar;192(3):815-25.