What is the cause of fat necrosis?

What is the Cause of Fat Necrosis?

Fat necrosis results from direct tissue injury through trauma, ischemia, enzymatic destruction (particularly pancreatic lipase), or metabolic derangements that compromise adipocyte viability.

Primary Mechanisms of Fat Necrosis

Enzymatic Fat Necrosis

• Pancreatic lipase and colipase are the primary causative agents in pancreatic-associated fat necrosis, escaping from the pancreas during pancreatitis, pancreatic carcinoma, or pancreatic trauma 1
• In acinar cell carcinoma of the pancreas, overproduction of lipase leads to metastatic fat necrosis syndrome, characterized by peripheral fat necrosis, eosinophilia, and polyarthralgias 2
• Pancreatic necrosis itself is defined as diffuse or focal areas of non-viable pancreatic parenchyma, typically associated with peripancreatic fat necrosis 3
• The two primary causes of necrotizing pancreatitis (which leads to enzymatic fat necrosis) are gallstones and excessive alcohol consumption, accounting for 75-80% of cases 3

Traumatic Fat Necrosis

• Blunt trauma to adipose tissue directly causes fat cell death through mechanical disruption, leading to subsequent inflammatory response and necrosis 4
• Falls, direct blunt injury, surgery, and minor procedures or injections can all precipitate posttraumatic fat necrosis 4
• In approximately one-third of patients with alpha-1 antitrypsin deficiency-associated panniculitis, trauma precipitates the necrotizing panniculitis 2

Ischemic Fat Necrosis

• Vascular compromise through torsion or infarction causes fat necrosis, as seen with torsion of epiploic appendages or infarction of the greater omentum 5
• Fat necrosis is a well-known complication of free tissue transfer where inadequate perfusion leads to adipocyte death 6

Metabolic and Systemic Causes

• Alpha-1 antitrypsin (AAT) deficiency causes necrotizing panniculitis through mechanisms involving protease-antiprotease imbalance, leading to spontaneous ulcerations with drainage of oily fluid 2
• Fat embolism syndrome involves fat globules entering the circulation after long bone fractures, with subsequent inflammatory cascade causing tissue damage 7, 8

Distribution Patterns

Localized Fat Necrosis

• Direct contact with pancreatic enzymes causes peritoneal-retroperitoneal fat necrosis in pancreatic disease 1
• Surgical sites and areas of fat grafting develop localized fat necrosis through ischemia and trauma 6

Systemic Fat Necrosis

• Pancreatic lipase can reach peripheral tissues via circulation, causing subcutaneous fat necrosis throughout the body, polyarthritis in hand and foot joints, and osteolytic bone marrow defects 1
• AAT deficiency-associated panniculitis typically starts with painful nodules on thighs and buttocks, progressing to ulcerations 2

Clinical Pitfalls

• Fat necrosis can mimic malignancy on imaging, including liposarcoma and peritoneal carcinomatosis, requiring knowledge of clinical history and prior imaging for accurate diagnosis 5
• Posttraumatic fat necrosis may present as chronic pain resembling reflex sympathetic dystrophy, not just as a palpable mass 4
• The precise mechanism by which pancreatic enzymes attack distant adipose tissue remains incompletely understood despite clear clinical associations 1