Fat necrosis. Gross specimen of peritoneal fat necrosis, or steatonecrosis, due to acute pancreatitis. The peritoneum is the membrane that lines the abdominal cavity. Pancreatitis is the inflammation of the pancreas, an organ that produces digestive enzymes and the hormone insulin. The disease is caused by digestive enzymes that become activated before they leave the pancreas and start to digest it. In this case the enzyme lipase has also started to digest fat outside of the digestive system. The fat is broken down into glycerol and fatty acids, which then react to form hard calcium soap lumps (pale).