Encapsulated Fat Necrosis

RLQ Pain in 56M with Ruptured Appendix 15 Years Ago • Xray of the Week 2016 • Week #35

This 56 year old male complained of chronic right lower quadrant pain and tenderness. He had a ruptured appendix 15 years ago, followed by appendectomy. CT guided biopsy was performed. What is the diagnosis?

Fig. 1 CT: Fatty mass in the right abdominal mesentery with a thin high attenuation capsule.

Pathologic analysis of the biopsy specimen demonstrated fat necrosis, and the patient was treated conservatively.

Fig. 2 CT: Fatty mass in the right abdominal mesentery with a thin high attenuation capsule (blue arrow). My biopsy needle (red arrow).

Encapsulated fat necrosis is due to necrotic fatty tissue organizing within a thin or thick fibrous capsule (1,2). It may cause pain and tenderness as it can be associated with inflammation and calcification (3). Since the imaging appearance may be similar with fatty tissue surrounded by a weakly enhancing capsule, and mild mass effect on adjacent structures (Fig. 2 blue arrows), the main concern in the differential diagnosis is liposarcoma (4-6). However, unlike liposarcoma, fat necrosis does not invade adjacent structures. As in this case, the history of prior surgery in the vicinity gives a clue to the correct diagnosis, as patients with encapsulated fat necrosis usually have a history of surgery (1,2). In addition, encapsulated fat necrosis remains stable or becomes smaller over time, whereas liposarcomas usually enlarge. The condition is considered a type of intraperitoneal focal fat infarction (7) along with omental infarction and epiploic appendagitis. As I did in this case, biopsy (Fig. 2 red arrow) can be performed to be certain of the diagnosis.

References:

1. Kamaya A, Federle MP, Desser TS. Imaging manifestations of abdominal fat necrosis and its mimics. Radiographics 2011. 31 (7): 2021-34.

2. Chan LP, Gee R, Keogh C, Munk PL. Imaging features of fat necrosis. AJR Am J Roentgenol 2003; 181(4):955–959.

3. Kiryu H, Rikihisa W, Furue M. Encapsulated fat necrosis: a clinicopathological study of 8 cases and a literature review. J Cutan Pathol 2000;27(1):19–23.

4. Takao H, Yamahira K, Watanabe T. Encapsulated fat necrosis mimicking abdominal liposarcoma: computed tomography findings. J Comput Assist Tomogr 2004;28(2):193–194.

5. Chen H, Tsang Y, Wu C, Su C, Hsu JC. Perirenal fat necrosis secondary to hemorrhagic pancreatitis, mimicking retroperitoneal liposarcoma: CT manifestation. Abdom Imaging 1996;21(6):546–548.

6. Andaç N, Baltacioglu F, Cimşit NC, Tüney D, Aktan O. Fat necrosis mimicking liposarcoma in a patient with pelvic lipomatosis: CT findings. Clin Imaging 2003;27(2):109–111.

7. Coulier B. Contribution of US and CT for diagnosis of intraperitoneal focal fat infarction (IFFI): a pictorial review. JBR-BTR. 2010;93 (4): 171-85.

Kevin M. Rice, MD is the president of Global Radiology CME

Dr. Rice serves as the Chair of the Radiology Department of Valley Presbyterian Hospital in Los Angeles, California and is a radiologist with Renaissance Imaging Medical Associates. Dr. Rice has made several media appearances and given as part of his ongoing commitment to public education. Dr. Rice's passion for state of the art radiology and teaching includes acting as a guest lecturer at UCLA. In 2015 Dr. Rice launched Global Radiology CME to provide innovative radiology education at exciting international destinations, with the world's foremost authorities in their field. In 2016, Dr. Rice was nominated and became a semifinalist for a "Minnie" award for the Most Effective Radiology Educator.

Follow Dr. Rice on Twitter @KevinRiceMD

All posts by Kevin M. Rice, MD