Table 1: Common imaging features of fat necrosis.

Mammography(i) Wide spectrum ranging from benign to indeterminate to malignant appearing masses or calcification
(ii) Visualized masses may be as follows: 
 (a) radiolucent with a thin, well-defined capsule
 (b) both radiolucent and dense with encapsulation
 (c) dense and circumscribed mass
 (d) mass with indistinct margins
 (e) mass with spiculated margins

Ultrasound(i) Sonographic spectrum with two most common appearances:
 (a) mass (anechoic, hypoechoic, isoechoic, or hyperechoic with or without shadowing and enhancement)
 (b) area of increased echogenicity of the subcutaneous tissue with or without small cysts and architectural distortion

CT(i) Liquefied fat demonstrates low attenuation coefficients
(ii) Fibrosis has attenuation similar to fibroglandular tissue or linear densities resembling fibrous bands
(iii) Inflammation enhances after contrast injection

PET-CT(i) Fat necrosis has increased FDG uptake secondary to presence of metabolically active inflammatory cells
(ii) It may show intense activity in the setting of TRAM flap reconstruction

MRI(i) Wide spectrum of appearance depending on amount of inflammatory reaction, liquefied fat, and degree of fibrosis
(ii) It may demonstrate enhancement following administration of IV paramagnetic contrast material depending on the intensity of the inflammatory process
(iii) Most common appearance are lipid cyst, round or oval mass with hypointense T1-weighted signal on fat saturation images
(iv) It is usually isointense to fat elsewhere in the breast
(v) “Black hole” sign, marked hypointensity on STIR images when compared with surrounding fat
(vi) It may mimic malignancy with thin, thick, irregular or spiculated enhancement