The Bottom Line: Ultrasound is the first-line imaging modality in most centers for the confirmation of the diagnosis of acute pancreatitis and the ruling out of other causes of acute abdomen, but it has limitations in the acute clinical setting. Computed tomography (CT) not only establishes the diagnosis of acute pancreatitis, but also enables to stage severity of the disease. Magnetic resonance imaging (MRI) has earned an ever more important role in the diagnosis of acute pancreatitis. It is especially useful for imaging of patients with iodine allergies, characterizing collections and assessment of an abnormal or disconnected pancreatic duct.
Reference: Turkvatan A, Erden A, Turkoglu MA, Secil M, Yener O. Imaging of acute pancreatitis and its complications. Part I: acute pancreatitis. Diagnostic and Interventional Imaging, 2015 Feb; 96(2): 151-160. doi:10.1016/j.diii.2013.12.017
For additional reading: Bollen TL. Imaging assessment of etiology and severity of acute pancreatitis. Pancreapedia: Exocrine Pancreas Knowledge Base, doi:10.3998/panc.2016.31
Summary: The purpose of imaging in acute pancreatitis is to confirm the clinical diagnosis, investigate the etiology and evaluate the extent and complications of the disease. Imaging modalities available for the diagnosis of acute pancreatitis include US, CT, MRI, magnetic resonance cholangiopancreatography (MRCP) and ERCP. The modality to be selected depends on the reason for investigation.
Ultrasound is quick and easy to perform examination and which is repetable, free of radiation and can be carried out at the bedside. However, this modality has technical limitations related to paralytic ileus accompanying in the first 48 hours of the disease. The advantage of US in the early period is that it allows to evaluate the gallbladder and biliary tract, and to detect gallstones and dilatation of the bile ducts. Pancreas may be seen normal in the cases of mild acute pancreatitis. In 30% of the cases, pancreatic enlargement and decreased parenchymal echogenicity due to interstitial edema may be seen.
CT: In the cases with acute pancreatitis, CT examination should be performed if the clinical diagnosis is uncertain, clinical findings suggest severe acute pancreatitis (Ranson score ≥ 3, APACHE II score ≥ 8), or there is suspicion of necrotizing pancreatitis, and for patients who do not improve clinically within 72 hours of the initial conservative medical therapy or for patients who demonstrate improvement during the initial medical therapy but then manifest acute change in clinical status with fever, pain, decrease in hematocrit or hypotension, and any complication is suspected. The ideal time for assessing these complications with CT is after 72 hours from onset of symptoms.