Revision 137 for 'Acute pancreatitis'

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Acute pancreatitis

Acute pancreatitis (plural: pancreatitides) is an 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:

  • acute onset of persistent, severe epigastric pain (i.e. pain consistent with acute pancreatitis)
  • lipase/amylase elevation >3 times the upper limit of normal
  • characteristic imaging features on contrast-enhanced CT, MRI, or ultrasound

Imaging is only required to establish the diagnosis if the first two criteria are not met. Imaging is crucial for the detection of complications and to help guide treatment.

Terminology

There are two subtypes of acute pancreatitis as described by the Revised Atlanta Classification 8

Epidemiology

The demographics of patients affected by acute pancreatitis reflects the underlying cause, of which there are many, including: 

See: causes of pancreatitis (mnemonic)

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

A normal amylase level (normoamylasaemia) in acute pancreatitis is well-recognized, especially when it occurs on a background of chronic pancreatitis. A normal lipase level has also been reported (<10 case reports) but is extremely rare 16.

(Rare) signs of hemorrhage on the physical exam 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 notwithstanding, 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

Radiographic features

The role of imaging is manifold: 

  • to clarify the diagnosis when the clinical picture is confusing
  • to assess severity (Balthazar score) and thus to determine prognosis
  • to detect complications
  • to determine possible causes

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
    • the presence of gas is helpful (emphysematous pancreatitis)
    • 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
  • calcification
    • evidence of background chronic pancreatitis
Dual-energy CT

Dual-energy CT may be able to help better differentiate necrotic debris, hematoma and areas of viable tissue in cases of necrotizing pancreatitis. In hemorrhagic pancreatitis virtual non-enhanced images can depict hematoma and differentiate it from parenchymal enhancement on contrast-enhanced images. It also allows detection of non-calcified gallstones and isoattenuating cholesterol stones which may be the causative factor in the patient's pancreatitis 21.

Dual-energy CT dual phase protocols with a virtual non-enhanced reformat can also offer lower radiation doses than conventional triple-phase CT imaging of the pancreas 21.

MRI

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

Ultrasound

The main role of ultrasound is: 

  • to identify gallstones as a possible cause
  • diagnosis of vascular complications, e.g. thrombosis
  • identify areas of necrosis which appear as hypoechoic regions
  • assessment of clinically similar etiologies of an acute abdomen

In the event of a serendipitously patent acoustic window, typical ultrasonographic features congruent with acute pancreatitis include:

  • increased pancreatic volume with a marked decrease in echogenicity 19 
    • volume increase quantified as a pancreatic body exceeding 2.4cm in diameter, with marked anterior bowing and surface irregularity 17
    • decreased echogenicity secondary to fluid exudation, which may result in a marked heterogeneity of the parenchyma 18
  • displacement of the adjacent transverse colon and/or stomach secondary to pancreatic volume expansion 20

Treatment and prognosis

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. 

Recommendations include 11:

  • aggressive fluid resuscitation in first 24 hours
  • no need for prophylactic antibiotics
  • enteral feeding strongly preferred over parenteral feeding, especially in severe acute pancreatitis
  • no need for ERCP in acute gallstone pancreatitis unless evidence of ascending cholangitis
  • image-directed catheter placement is an alternative to surgical drainage of pancreatic fluid collections
  • cholecystectomy before discharge in patients with acute pancreatitis and gallstones found on imaging

Prognosis for acute pancreatitis varies according to severity. Overall mortality is 5-10% per attack 3. Various scoring systems exist that attempt to stratify severity (e.g. Ranson's criteria and APACHE II).

The 2016 revised Atlanta classification attempts to establish uniformity in reporting for both clinical practice and research 8.

Differential diagnosis

General imaging differential considerations include:

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