Table 1.

Collections as defined in the Revised Atlanta Classification

Revised Atlanta Classification terms
Interstitial Edematous Pancreatitis	Necrotizing Pancreatitis
Acute inflammation of the pancreatic parenchyma and peripancreatic tissues, but without recognizable necrosis of pancreatic parenchyma or peripancreatic tissues.	Inflammation associated with pancreatic parenchymal necrosis and/or peripancreatic necrosis.
AFC (Acute Fluid Collection)	ANC (Acute Necrotic Collection)	EARLY
Peripancreatic fluid associated with IEP with no associated peripancreatic necrosis. This term applies only to areas of peripancreatic fluid seen within the first 4 weeks after onset of IEP.	A collection containing variable amounts of both fluid and necrosis associated with necrotizing pancreatitis; the necrosis can involve the pancreatic parenchyma and/or the peripancreatic tissues.	(1st 4 weeks after onset of pancreatitis)
CT Criteria: Occurs in the setting of acute interstitial edematous pancreatitis Collection present Adjacent to pancreas (no intrapancreatic extension) Confined by normal peripancreatic fascial planes No complete definable wall Homogeneous collection with fluid density	CT Criteria: Occurs only in the setting of acute necrotizing pancreatitis Collection present Location: intrapancreatic and/or extrapancreatic No complete definable wall Heterogeneous and non-liquid density with varying degrees of loculation (some appear homogeneous early in their course)
Pancreatic Pseudocyst	WON (Walled-Off Necrosis)	LATE
A complete encapsulated collection of fluid outside the pancreas with minimal (< 5%) or no necrosis usually requires more than 4 weeks after onset of IEP to mature and has a well defined inflammatory wall; rarely a pancreatic pseudocyst may develop in a patient with necrotizing pancreatitis after treatment by necrosectomy, usually related to disconnected duct syndrome.	A encapsulated collection of pancreatic and/or peripancreatic necrosis that persists for > 4 weeks after onset of necrotizing pancreatitis and has a well-defined inflammatory wall.	(≥4 weeks after onset of pancreatitis)
CT Criteria: Well defined wall; i.e. completely encapsulated Homogeneous fluid density No non-liquid component Well circumscribed, usually round or oval Maturation usually requires > 4 weeks after onset of acute pancreatitis; usually occurs after interstitial edematous pancreatitis, but may occur rarely after necrotizing pancreatitis	CT Criteria: Location: intrapancreatic and/or extrapancreatic Well-defined wall, i.e. completely encapsulated Heterogeneous with liquid and non-liquid density with varying degrees of loculations, (some may appear homogenous) Maturation usually requires 4 weeks after onset of acute necrotizing pancreatitis.

IEP, interstitial edematous pancreatitis.