ARRS 2022 Abstracts

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E1033. Pick a Number Between 1 and 6: Postoperative Fat Necrosis and BI-RADS Pictorial
Authors
  1. Eric Fromke; University of North Carolina at Chapel Hill
  2. Barry Keane; University of North Carolina at Chapel Hill
  3. Sheryl Jordan; University of North Carolina at Chapel Hill
Background
Breast conserving therapy (BCT) and breast oncoplastic reconstruction are increasingly popular and aesthetically pleasing methods of treating breast cancer, while reduction mammaplasty carries high patient satisfaction. Oncoplastic operations relocate breast tissue and can disrupt perforating arteries to adipose tissue. Other breast surgeries may yield similar impact and adipose cells may undergo fat necrosis as their blood supply is interrupted. Fat necrosis, while benign, presents in a variety of manners depending on its stage and extent of inflammation and fibrosis. It often mimics tumor recurrence – running the gamut of BI-RADS 2–5. In a post-surgical breast with architectural distortion and possibly baseline calcifications, distinguishing between fat necrosis and malignancy is even more difficult but extremely important.

Educational Goals / Teaching Points
In this exhibit, learners will understand the definition and causes of fat necrosis while being introduced to breast oncoplasty and reviewing other breast surgeries. Learners will identify imaging features of fat necrosis and its varying BI-RADS classifications on mammography, ultrasound, and MRI. The exhibit’s goal is equipping learners to distinguish fat necrosis from tumor recurrence in the post-operative breast. Fat necrosis cases will be presented according to BI-RADS classifications ranging from 2 to 5.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Fat necrosis is a benign entity often secondary to trauma or surgery that causes an ischemic insult and necrosis of adipose tissue with an ensuing inflammatory response. Imaging findings vary on differing modalities. We present several cases representing the various presentations of fat necrosis of the breast on imaging, using representative cases spanning BI-RADS 2 to 5, with pertinent and unique imaging findings and teaching points. Many of these cases represent the post-breast oncoplasty patient, where the imager will learn to distinguish between fat necrosis and tumor recurrence, with imaging pearls and unique representative images. The MRI findings of fat necrosis depend on the degree of fibrosis and fat present. Fat necrosis classically presents as round oil cysts with hypointense T1-weighted signal on fat saturation imaging. On T1-weighted non-fat saturation, fat necrosis is isointense to breast fat. Fat necrosis lesions can enhance secondary to an inflammatory response. The more fibrotic the lesion gets, the more spiculated the lesion can appear, and the more difficult it is to distinguish from malignancy. Fat necrosis can also present suspiciously as new coarse calcifications or a developing irregular spiculated mass in or near lumpectomy beds. Several of these findings may warrant use of BI-RADS 4 or 5 if particularly concerning.

Conclusion
Fat necrosis can present in a variety of ways on various imaging modalities. It is a benign but common malignancy mimicker in the post surgical breast (oncoplasty, BCT, reduction). Thus, it is important for the radiologist to effectively discern between fat necrosis and malignancy, given the impact to alter patient care.