Pancreatic Pseudocyst

Basics

• A pancreatic pseudocyst is a peripancreatic (or intrapancreatic) fluid collection associated with a history of pancreatitis, that is surrounded by a well-defined inflammatory wall and that has no solid component.
  • The term “pseudocyst” is often incorrectly used to define various types of fluid collections associated with pancreatitis. As a result, medical literature on pseudocysts is not consistent in its descriptions or its findings.
  • An important distinction between “fluid collections” associated with pancreatitis is that some consist of fluid alone, whereas others arise from necrosis of pancreatic parenchyma and/or peripancreatic tissues. The latter type of fluid collection involves a solid component (with variable amounts of fluid), which distinguishes them from pseudocysts.
• Types of fluid collections:
  • Acute peripancreatic fluid collection (APFC)
    • A fluid collection that develops in the early phase of interstitial edematous acute (typically mild) pancreatitis
    • Lack a well-defined wall on CT scan
    • Not associated with necrotizing pancreatitis
    • Remains sterile and usually resolves without intervention
    • If APFC persists beyond 4 weeks, likely to develop into a pancreatic pseudocyst, although this is considered a rare outcome
  • Pancreatic pseudocyst
    • Refers specifically to a peripancreatic (or less commonly, an intrapancreatic) fluid collection
    • Surrounded by a well-defined inflammatory wall and containing no solid material
    • Pancreatic pseudocysts develop >4 weeks after the onset of interstitial pancreatitis.
  • Acute necrotic collection (ANC)
    • A collection of both variable amounts of fluid and solid (necrotic) material related to pancreatic and/or peripancreatic necrosis
    • Occur within the first 4 weeks of disease and can resemble an APFC in the first few days of acute pancreatitis
    • As necrotizing pancreatitis develops and necrosis evolves, solid component become evident.
    • May be multiple and may involve the pancreatic parenchyma alone, the peripancreatic tissue alone, or most commonly both
    • May be infected or sterile
    • Generally associated with more severe sequelae of acute pancreatitis
  • Walled-off necrosis (WON)
    • Collection of varying amounts of liquid and solid material surrounded by a mature, enhancing wall of reactive tissue
    • Represents a mature, encapsulated ANC
    • Develops no earlier than 4 weeks after episode of necrotizing pancreatitis
    • May be multiple and present at sites distant from the pancreas
    • May be sterile or infected