Types of pancreatic and peripancreatic collections that may occur in the setting of acute pancreatitis
- 1. Acute peripancreatic fluid collections (APFC) occur in the peripancreatic tissues within ≤ 4 weeks of symptom onset and have homogeneous fluid attenuation and signal intensity but have no discernible walls.
- 2. Pseudocysts occur in the peripancreatic tissues usually after >4 weeks of symptom onset and are well-circumscribed round or oval collections with homogeneous fluid attenuation and signal intensity, with discernible enhancing nonepithelialized walls made of fibrous or granulation tissue. The majority of pseudocysts spontaneously resolve, whereas ones that are >4 to 6 cm in size, are increasing in size, are associated with symptoms, or are superinfected may require drainage.
- 3. Acute necrotic collections (ANC) may occur in the pancreas or peripancreatic tissues within ≤ 4 weeks of symptom onset, have heterogeneous attenuation and signal intensity with nonliquefied necrotic material and are variably loculated but have no discernible walls.
- 4. Walled-off necrosis (WON) may occur in the pancreas or peripancreatic tissues after >4 weeks of symptom onset, have heterogeneous attenuation and signal intensity with nonliquefied necrotic material, are variably loculated, and have discernible enhancing walls.
Superinfection of any of these collections may occur and is suspected when foci of very low attenuation and very low signal intensity gas are seen in a collection. However, presence of gas may alternatively be caused by fistulization of a collection with the gastrointestinal tract or by prior intervention. When infection is present, percutaneous, endoscopic, or surgical intervention is usually required.
