Imaging spectrum of Abdominal Fat Necrosis

1. Imaging spectrum of Abdominal Fat Necrosis
1. Dr Anuj Kumar, PGJR Radiodiagnosis, GMCH, Chandigarh
2. Dr Rekha Gupta, Associate Professor, Radiodiagnosis,
GMCH, Chandigarh

2. INTRODUCTION:
• Abdominal fat necrosis (FN) is a common finding which mimicks more sinister conditions causing
acute abdomen requiring surgical intervention like acute appendicitis, cholecystitis, renal colic or
recurrence of previous malignancy or can be asymptomatic. It can be primary FN or secondary FN
accompanying various other pathophysiologic processes causing metabolic and mechanical trauma
to fat. FN involving mesenteric and retroperitoneal fat has characteristic cross-sectional imaging
appearance, depending on the stage of temporal evolution of disease. Imaging thus helps localise
the pathology and avoid unnecessary operative intervention. Correct diagnosis depends on the
imaging appearances, clinical features and comparison with previous imaging (wherever
applicable).
• Encapsulated fat degeneration is usually caused by trauma and ischemia and was first described in
1975 in breast but can occur anywhere in body. Fat then organises by thin fibrous capsule which
might show mild postcontrast enhancement and mild mass effect which may simulate liposarcoma.
However, decrease in size over time and noninvasion of surrounding structures in appropriate
clinical scenario help clinch the correct diagnosis. In ambiguous cases, histopathologic
confirmation of underlying inflammation might be necessary.

3. Fat Necrosis commonly accompanies episodes of acute pancreatitis. Lipophilic enzymes released during
pancreatitis also cause fat saponification and activate inflammatory processes. This leads to delayed
appearance of scattered nodules in the peritoneal cavity particularly retroperitoneum showing mild mass effect
and delayed contrast enhancement due to leaking capillaries in the inflammation. Clinical history and previous
imaging help exclude a diagnosis of peritoneal carcinomatosis.
Fig. a) shows circumscribed fatty
attenuation area abutting
descending colon surrounded by
fibrous capsule s/o epiploic
appendagitis
Fig. b) shows omental
torsion and infarction
in a postoperative
patient with small
bowel obstruction
Fig. c) shows extensive nodular peri-
pancreatic fat necrosis extending in
left anterior pararenal space in a
patient with pancreatitis
a) b) c)

4. Fig. a) and b) show liquefied fat necrosis in infraumbilical region in a post-
hemicolectomy patient of cecal adenocarcinoma. Patient presented with pain and
fullness lower abdomen with clinical suspicion of recurrence and HPE revealed
inflammatory collection s/o Delayed fat necrosis. Immediate postoperative scan
revealed heterogenous fat stranding in the same area.
a) b)

5. a)
b)
Fig. a) and b): 21 year old patient with suspected renal colic and
imaging revealed an area of unsuspected fat necrosis abutting the
inferior pole of right kidney. Patient was treated conservatively.
c)
Fig. c) shows circumscribed area of
subcutaneous fat necrosis in a 60 year
old nondiabetic female and HPE revealed
inflammatory cells with dry tap.

6. CONCLUSION:
Intraperitoneal fat is metabolically active and is affected by ischemia due to various
etiologies. Omental infarction and epiploic appendagitis are two commonly
encountered pathologies mimicking acute abdomen. However, postoperative and
post-pancreatitis fat necrosis is also not uncommon .
It is important to be familiar with imaging manifestations of these entities as
management is frequently conservative. Equivocal cases can be confirmed by
histopathology.