Necrotizing pancreatitis: Diagnose, treat, consult
ABSTRACT
Necrosis significantly increases rates of morbidity and mortality in acute pancreatitis. Hospitalists and general internists are on the front lines in identifying severe cases and consulting the appropriate specialists for optimal multidisciplinary care.
KEY POINTS
- Selective and appropriate timing of radiologic imaging is vital in managing necrotizing pancreatitis. Protocols are valuable tools.
- While the primary indication for debridement and drainage in necrotizing pancreatitis is infection, other indications are symptomatic walled-off pancreatic necrosis, intractable abdominal pain, bowel obstruction, and failure to thrive.
- Open surgical necrosectomy remains an important treatment for infected pancreatic necrosis or intractable symptoms.
- A “step-up” approach starting with a minimally invasive procedure and escalating if the initial intervention is unsuccessful is gradually becoming the standard of care.
ROLE OF IMAGING
Radiographic imaging is not usually necessary to diagnose acute pancreatitis. However, it can be a valuable tool to clarify an ambiguous presentation, determine severity, and identify complications.
The timing and appropriate type of imaging are integral to obtaining useful data. Any imaging obtained in acute pancreatitis to evaluate necrosis should be performed at least 3 to 5 days from the initial symptom onset; if imaging is obtained before 72 hours, necrosis cannot be confidently excluded.8
COMPUTED TOMOGRAPHY
CT is the imaging test of choice when evaluating acute pancreatitis. In addition, almost all percutaneous interventions are performed with CT guidance. The Balthazar score is the most well-known CT severity index. It is calculated based on the degree of inflammation, acute fluid collections, and parenchymal necrosis.9 However, a modified severity index incorporates extrapancreatic complications such as ascites and vascular compromise and was found to more strongly correlate with outcomes than the standard Balthazar score.10
Contrast-enhanced CT is performed in 2 phases:
The pancreatic parenchymal phase
The pancreatic parenchymal or late arterial phase is obtained approximately 40 to 45 seconds after the start of the contrast bolus. It is used to detect necrosis in the early phase of acute pancreatitis and to assess the peripancreatic arteries for pseudoaneurysms in the late phase of acute pancreatitis.11
Pancreatic necrosis appears as an area of decreased parenchymal enhancement, either well-defined or heterogeneous. The normal pancreatic parenchyma has a postcontrast enhancement pattern similar to that of the spleen. Parenchyma that does not enhance to the same degree is considered necrotic. The severity of necrosis is graded based on the percentage of the pancreas involved (< 30%, 30%–50%, or > 50%), and a higher percentage correlates with a worse outcome.12,13
Peripancreatic necrosis is harder to detect, as there is no method to assess fat enhancement as there is with pancreatic parenchymal enhancement. In general, radiologists assume that heterogeneous peripancreatic changes, including areas of fat, fluid, and soft tissue attenuation, are consistent with peripancreatic necrosis. After 7 to 10 days, if these changes become more homogeneous and confluent with a more mass-like process, peripancreatic necrosis can be more confidently identified.12,13
The portal venous phase
The later, portal venous phase of the scan is obtained approximately 70 seconds after the start of the contrast bolus. It is used to detect and characterize fluid collections and venous complications of the disease.
Drawbacks of CT
A drawback of CT is the need for iodinated intravenous contrast media, which in severely ill patients may precipitate or worsen pre-existing acute kidney injury.
Further, several studies have shown that findings on CT rarely alter the management of patients in the early phase of acute pancreatitis and in fact may be an overuse of medical resources.14 Unless there are confounding clinical signs or symptoms, CT should be delayed for at least 72 hours.9,10,14,15
MAGNETIC RESONANCE IMAGING
Magnetic resonance imaging (MRI) is not a first-line imaging test in this disease because it is not as available as CT and takes longer to perform—20 to 30 minutes. The patient must be evaluated for candidacy, as it is difficult for acutely ill patients to tolerate an examination that takes this long and requires them to hold their breath multiple times.
MRI is an appropriate alternative in patients who are pregnant or who have severe iodinated-contrast allergy. While contrast is necessary to detect pancreatic necrosis with CT, MRI can detect necrosis without the need for contrast in patients with acute kidney injury or severe chronic kidney disease. Also, MRI may be better in complicated cases requiring repeated imaging because it does not expose the patient to radiation.
On MRI, pancreatic necrosis appears as a heterogeneous area, owing to its liquid and solid components. Liquid components appear hyperintense, and solid components hypointense, on T2 fluid-weighted imaging. This ability to differentiate the components of a walled-off pancreatic necrosis can be useful in determining whether a collection requires drainage or debridement. MRI is also more sensitive for hemorrhagic complications, best seen on T1 fat-weighted images.12,16
Magnetic resonance cholangiopancreatography is an excellent method for ductal evaluation through heavily T2-weighted imaging. It is more sensitive than CT for detecting common bile duct stones and can also detect pancreatic duct strictures or extravasation into fluid collections.16
SUPPORTIVE MANAGEMENT OF EARLY NECROTIZING PANCREATITIS
In the early phase of necrotizing pancreatitis, management is supportive with the primary aim of preventing intravascular volume depletion. Aggressive fluid resuscitation in the first 48 to 72 hours, pain control, and bowel rest are the mainstays of supportive therapy. Intensive care may be necessary if organ failure and hemodynamic instability accompany necrotizing pancreatitis.
Prophylactic antibiotic and antifungal therapy to prevent infected necrosis has been controversial. Recent studies of its utility have not yielded supportive results, and the American College of Gastroenterology and the Infectious Diseases Society of America no longer recommend it.9,17 These medications should not be given unless concomitant cholangitis or extrapancreatic infection is clinically suspected.
Early enteral nutrition is recommended in patients in whom pancreatitis is predicted to be severe and in those not expected to resume oral intake within 5 to 7 days. Enteral nutrition most commonly involves bedside or endoscopic placement of a nasojejunal feeding tube and collaboration with a nutritionist to determine protein-caloric requirements.
Compared with enteral nutrition, total parenteral nutrition is associated with higher rates of infection, multiorgan dysfunction and failure, and death.18
