Fat necrosis
Fat necrosis is necrosis affecting fat tissue from various injuries.
Fat necrosis is a form of cell death that occurs in adipose (fat) tissue. Although the term is widely used in medicine, it does not describe a single, specific pattern of tissue death. The condition can be triggered by a range of injuries to fat cells, such as physical force, the breakdown of adipocytes by lipase enzymes, radiation exposure, lack of oxygen, or inflammation of the subcutaneous fat layer (panniculitis).
When examined with the naked eye, fat necrosis typically appears as irregular, chalky white patches within otherwise normal fat. In rare instances, it may present as a mobile, firm, fibrous nodule located just beneath the skin.
**Pathophysiology**
*Trauma*: Physical injury to fat tissue releases stored fat and lipases from the fat cells. This extracellular fat quickly triggers an inflammatory response, drawing in macrophages and polymorphonuclear leukocytes that engulf the freed fat. Over time, this process leads to fibrosis. The dead tissue can eventually form a palpable lump, especially in superficial areas like the breast. Traumatic fat necrosis in the breast often mimics a tumor, particularly if the necrotic mass becomes calcified.
*Enzymatic digestion*: Conditions affecting the pancreas—such as acute pancreatitis, pancreatic cancer, or pancreatic injury—can release pancreatic lipase into surrounding tissue. This enzyme digests fat, producing free fatty acids that then combine with calcium to form soapy, chalky deposits. While the area around the pancreas is most commonly affected due to direct enzyme exposure, fat necrosis can also occur elsewhere in the body, including subcutaneous tissue, joints of the hands and feet, and bone marrow. These distant complications are known as pancreatic panniculitis.
**Clinical significance: Breast fat necrosis**
*Causes*: Numerous factors can lead to breast fat necrosis, including breast trauma (for instance, from a seat belt during a car accident), breast surgery, fine-needle aspiration biopsy, radiotherapy, lumpectomy, reduction mammoplasty, breast reconstruction, pancreatic disease (acute pancreatitis, pancreatic cancer, pancreatic injury), certain forms of panniculitis (such as subcutaneous fat necrosis of the newborn or Weber–Christian disease), and polyarteritis nodosa.
*Epidemiology*: Accidental trauma is the most common cause, accounting for 21–70% of cases, often due to seat-belt injury.
Quick Facts
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Lore & Background
Fat necrosis results from injuries such as physical trauma, enzymatic digestion by lipases, radiation therapy, hypoxia, or panniculitis. Traumatic injury liberates stored fat and lipases, attracting macrophages and polymorphonuclear leukocytes that phagocytose the freed fat, eventually leading to fibrosis. The necrotic tissue may form a palpable mass, especially in superficial sites like the breast. Pancreatic conditions like acute pancreatitis, pancreatic carcinoma, and pancreatic trauma liberate pancreatic lipase, which digests fat to form free fatty acids that combine with calcium to create soapy precipitates. Although the peripancreatic region is most commonly affected, associated fat necrosis may occur throughout the body in subcutaneous tissue, hand and foot joints, and bone marrow, known as pancreatic panniculitis.
Reader's Guide
Fat necrosis is clinically significant, particularly in the breast. Causes include breast trauma (e.g., seat belt injury), breast surgery, fine needle aspiration biopsy, radiotherapy, lumpectomy, reduction mammoplasty, breast reconstruction, pancreatic disease, and some forms of panniculitis. Accidental trauma is the most common cause of breast fat necrosis, accounting for 21-70% of cases, often due to seat-belt injury. Symptomatic breast fat necrosis occurs after around 25% of free flap reconstructive surgeries, much higher than the 3% rate in pedicled flap approaches. It is less common after breast cancer surgery (around 7%) and rates following fat graft surgery range from 2-18%. Middle-aged women with pendulous breasts are at higher risk for idiopathic breast fat necrosis. The gross appearance is an irregular, chalky white area within normal adipose tissue; rarely, mobile encapsulated fat necrosis appears as a mobile, firm, fibrous nodule deep to the skin.
Did You Know?
- Traumatic fat necrosis commonly affects the breast and may resemble a tumour, especially if calcification occurs.
- Pancreatic conditions like acute pancreatitis can cause fat necrosis throughout the body, known as pancreatic panniculitis.
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