What is the definition of acute pancreatitis?

Definition of Acute Pancreatitis

Acute pancreatitis is an acute inflammatory process of the pancreas, with variable involvement of other regional tissues or remote organ systems. 1 This definition comes from the Atlanta classification, which is the most widely accepted standard for defining and classifying acute pancreatitis.

Diagnostic Criteria

The diagnosis of acute pancreatitis requires at least two of the following three criteria:

1. Abdominal pain characteristic of acute pancreatitis (acute onset, severe, persistent, epigastric pain often radiating to the back)
2. Serum lipase or amylase levels at least three times the upper limit of normal
3. Characteristic findings of acute pancreatitis on imaging studies (CT, MRI, or ultrasound) 2

Classification of Severity

Acute pancreatitis is classified into three categories based on severity:

Mild Acute Pancreatitis

• Associated with minimal organ dysfunction and an uneventful recovery
• Predominant pathological feature is interstitial edema of the gland
• No organ failure, local or systemic complications
• Usually resolves within the first week 1

Moderately Severe Acute Pancreatitis

• Characterized by transient organ failure (resolving within 48 hours)
• May have local complications or exacerbation of comorbid diseases 1

Severe Acute Pancreatitis

• Associated with persistent organ failure (lasting more than 48 hours)
• Often associated with local complications such as necrosis (with or without infection), pseudocyst, or abscess
• Typically an expression of pancreatic necrosis, though patients with edematous pancreatitis may also manifest features of severe attack
• Comprises about 20-30% of cases with mortality rates of approximately 15% 1

Local Complications

Several local complications may develop during the course of acute pancreatitis:

1. Acute Fluid Collections

   • Occur early in the course of acute pancreatitis
   • Located in or near the pancreas
   • Lack a wall of granulation or fibrous tissue 1

2. Pancreatic Necrosis

   • Diffuse or focal area(s) of non-viable pancreatic parenchyma
   • Typically associated with peripancreatic fat necrosis
   • Can become infected, which triples mortality risk 1

3. Acute Pseudocyst

   • Collection of pancreatic juice enclosed in a wall of fibrous or granulation tissue
   • Arises following an attack of acute pancreatitis
   • Formation requires four or more weeks from onset 1

4. Pancreatic Abscess

   • Circumscribed intra-abdominal collection of pus
   • Usually in proximity to the pancreas
   • Contains little or no pancreatic necrosis 1

5. Walled-off Necrosis (WON)

   • Mature, encapsulated collection of pancreatic and/or peripancreatic necrosis
   • Has a well-defined inflammatory wall
   • Usually develops ≥4 weeks after onset of necrotizing pancreatitis 1, 3

Clinical Course

The clinical course of acute pancreatitis typically follows two phases:

1. Early Phase (first week)

   • Characterized by systemic inflammatory response syndrome (SIRS)
   • About one-third of deaths occur during this phase due to multiple organ failure 1
   • Major fluid deficit occurs early, requiring aggressive fluid replacement 1

2. Late Phase (after first week)

   • Most deaths occurring after the first week are due to infectious complications
   • Particularly infected pancreatic necrosis 1, 3

Understanding this definition and classification system is crucial for appropriate management and risk stratification of patients with acute pancreatitis, as treatment approaches differ significantly based on disease severity and complications.