Revision 98 for 'Acute pancreatitis'

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Acute pancreatitis

Acute pancreatitis refers to acute inflammation of the pancreas and is a potentially life threatening condition.

The diagnosis of acute pancreatitis is made by fulfilling two of the following three criteria 8:

  1. Acute onset of persistent, severe epigastric pain (i.e. pain consistent with acute pancreatitis).
  2. Lipase/amylase elevation beyond three times the upper limit of normal. 
  3. Characteristic imaging features on CECT, MRI or US. 

Imaging is required to confirm the diagnosis if the first two criteria are not met. It can also be used to assess for complications and guide treatment.

Terminology

There are two subtypes of acute pancreatitis 8

Epidemiology

The demographics of patients affected by acute pancreatitis reflects the underlying cause. Causes include:

Clinical presentation

Classical clinical features include 3:

  • acute onset of severe central epigastric pain (over 30-60 min)
  • poorly localized tenderness and pain
  • exacerbated by supine positioning
  • radiates through to the back in 50% of patients

Elevation of amylase and lipase are 90-95% specific for the diagnosis 3.

Signs of hemorrhage include:

Pathology

There continues to be debate over the precipitating factor leading to acute pancreatitis, with duct occlusion being an important factor, but neither necessary nor sufficient.

Mechanism not withstanding, activation of pancreatic enzymes within the pancreas rather than the bowel lead to inflammation of the pancreatic tissue, disruption of small pancreatic ducts and in leakage of pancreatic secretions. Because the pancreas lacks a capsule, the pancreatic juices have ready access to surrounding tissues. Pancreatic enzymes digest fascial layers, spreading the inflammatory process to multiple anatomic compartments.

Complications
  • pancreatic fluid collections are defined by presence or absence of necrosis:
  • liquefactive necrosis of pancreatic parenchyma (i.e. necrotizing pancreatitis)
  • pancreatic abscess
    • presence of infection without significant necrosis
    • extremely rare
    • term not in current use 8
  • vascular complications
    • hemorrhage: resulting from erosion of blood vessels and tissue necrosis
    • pseudoaneurysm: autodigestion of arterial walls by pancreatic enzymes results in pulsatile mass that is lined by fibrous tissue and maintains communication with parent artery
    • splenic vein thrombosis
    • portal vein thrombosis
  • fistula formation with pancreatic ascites: leakage of pancreatic secretions into peritoneal cavity

Radiographic features

Role of imaging is either to clarify the diagnosis when the clinical picture is confusing, to assess severity (Balthazar score), to determine prognosis, or to detect complications.

Imaging studies of acute pancreatitis may be normal in mild cases. Contrast-enhanced CT provides the most comprehensive initial assessment, typically with a dual phase (arterial and portal venous) protocol. However, US is useful for follow-up of specific abnormalities, such as fluid collections and pseudocysts.

CT

Abnormalities that may be seen in the pancreas include:

  • typical findings
    • focal or diffuse parenchymal enlargement
    • changes in density because of edema
    • indistinct pancreatic margins owing to inflammation
    • surrounding retroperitoneal fat stranding
  • liquefactive necrosis of pancreatic parenchyma
    • lack of parenchymal enhancement
    • often multifocal
  • infected necrosis
    • difficult to distinguish from aseptic liquefactive necrosis
    • presence of gas is helpful
    • FNA helpful
  • abscess formation
    • circumscribed fluid collection
    • little or no necrotic tissues (thus distinguishing it from infected necrosis)
  • hemorrhage
    • high-attenuation fluid in the retroperitoneum or peripancreatic tissues
MRI

Contrast-enhanced MR is equivalent to CT in the assessment of pancreatitis.

Ultrasound

May be used to monitor patient's progress:

  • diagnosis of vascular complications, i.e. thrombosis
  • identify gallstones
  • hypoechoic lesions may indicate necrotic change

Treatment and prognosis

Prognosis for acute pancreatitis varies according to severity. Overall mortality is 5-10% per attack 3. Ranson's criteria are useful in prognosticating.

The newly revised Atlanta classification system makes the scene for a new international classification system, trying to uniform reporting for both clinical practice and research 8.

Treatment is largely supportive, often requiring ICU care in severe cases for respiratory and cardiovascular support and careful management of glucose, calcium and fluid balance.

Ultrasound or CT directed aspiration biopsy may be needed to confirm the presence of pancreatic abscess. Image-directed catheter placement is an alternative to surgical drainage of pancreatic fluid collections.

Differential diagnosis

General imaging differential considerations include:

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