Imaging of Acute Pancreatitis

Etiology

Acute pancreatitis is an acute inflammatory disorder of the pancreas that has numerous causes ( Box 48-1 ). The most common risk factors are chronic alcohol consumption and choledocholithiasis. In 20% of cases no cause can be found.

Prevalence and Epidemiology

In the United States, up to 210,000 patients per year are admitted to a hospital for acute pancreatitis. The spectrum of acute pancreatitis ranges from mild to severe and fatal.

In 1992, the International Symposium on Acute Pancreatitis in Atlanta, Georgia, established a clinical-based classification and defined certain terminologies commonly associated with acute pancreatitis. Acute pancreatitis is classified as mild and severe based on the presence of local complications and organ failure. This classification helped identify patients with severe disease who required close monitoring and intensive unit care. Mild acute pancreatitis has a mortality rate of less than 1%, whereas the death rate for severe pancreatitis is much higher—10% with sterile and 30% with infected pancreatic necrosis.

Clinical Presentation

The hallmark symptom of acute pancreatitis is the acute onset of persistent upper abdominal pain, usually with nausea and vomiting. The pain may radiate to the back, chest, flanks, and lower abdomen. Physical examination findings include fever, hypotension, severe abdominal tenderness, guarding, respiratory distress, and abdominal distention.

Pathophysiology

The inflammatory process in acute pancreatitis is triggered by the premature activation of pancreatic enzymes with resultant autodigestion of the pancreatic parenchyma. The inflammatory process may remain localized to the pancreas, spread to regional tissues, or even involve remote organ systems, resulting in multiple organ failure and occasionally death.

Mild acute pancreatitis (also known as interstitial or edematous pancreatitis) is more common and is a self-limiting disease with minimal organ dysfunction and an uneventful recovery. Pathologically, the mild form of acute pancreatitis is characterized by interstitial edema and infrequently by microscopic areas of parenchymal necrosis.

Severe acute pancreatitis (also known as necrotizing pancreatitis) occurs in 20% to 30% of all patients and is associated with organ failure and/or local complications, such as necrosis, abscess, or pseudocyst formation.

Pathology

Pathologic findings include macroscopic areas of focal or diffuse pancreatic necrosis, fat necrosis, and hemorrhage in the pancreas and peripancreatic tissues.

Imaging

Computed tomography (CT) and abdominal ultrasonography are routinely used in the setting of an acute abdomen to identify the source of pain. CT can help confirm the diagnosis of acute pancreatitis and exclude other causes of acute abdomen such as gastrointestinal perforation, acute cholecystitis, acute aortic dissection, and mesenteric artery occlusion, which can clinically mimic acute pancreatitis. In established cases of acute pancreatitis, contrast-enhanced CT is considered the gold standard for evaluating morphologic changes of acute pancreatitis, particularly in the assessment of pancreatic necrosis. Magnetic resonance imaging (MRI) with MR cholangiopancreatography (MRCP), endoscopic retrograde cholangiopancreatography (ERCP), endoscopic ultrasonography, and angiography have specific indications in a patient with known acute pancreatitis.