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Table 2 Common imaging features of fat necrosis

From: Fat necrosis in the Breast: A systematic review of clinical

MRI (1) Depending on amount of inflammatory reaction, liquefied fat, and degree of fibrosis, fat necrosis produces a wide spectrum of findings on MRI. Magnetic resonance images correlate well with the histology of fat necrosis.
(2) Depending on the intensity of the inflammatory process, it may show enhancement after the administration of IV paramagnetic contrast material.
(3) Lipid cyst, round or oval mass with hypointense T1-weighted signal on fat saturation images are the most common types of appearance.
(4) It is usually isointense to fat elsewhere in the breast. (v) Compared with surrounding fat, “black hole” sign is marked hypointensity on STIR images.
(5) MRI is associated with thin, thick, irregular or spiculated enhancement.
Mammography The mammographic appearance of fat necrosis includes normal appearance, discrete round or oval radiolucent oil cyst with thin capsule, thickening and deformity of skin and subcutaneous tissue, focal mass, and ill-defined spiculated mass. Oil cysts may be associated with uniform continuous eggshell calcification. There may also be multiple clustered pleomorphic micro-calcifications suspicious of malignancy. The most common mammographic findings are dystrophic calcifications, followed by radiolucent oil cysts.
Ultrasound Common features of fat necrosis on sonography are increased echogenicity of subcutaneous tissue, as an anechoic cyst with posterior acoustic enhancement, hypoechoic mass with posterior acoustic shadowing, solid mass, cyst with internal echoes, normal appearance or cystic mural nodule and architectural distortion
CT (1) Liquefied fat can manifest low attenuation coefficients.
(2) Similar to fibroglandular tissue or linear densities resembling fibrous bands, fibrosis has attenuation.
(3) Inflammation enhances followed by contrast injection.
PET-CT (1) Secondary to presence of metabolically active inflammatory cells, fat necrosis may increase FDG uptake.
(2) It is associated with intense activity in the setting of TRAM flap reconstruction.