Acute Pancreatitis

General characteristics

Acute pancreatitis arises in the majority of cases secondary to alcoholism or cholelithiasis. Alcohol-related acute pancreatitis most frequently results in acute recurrent pancreatitis, whereas gallstone-related pancreatitis typically results in a single attack.

Morphology

The signal-intensity features of the pancreas in uncomplicated mild acute pancreatitis resemble those of normal pancreatic tissue. The acutely inflamed pancreas shows either focal or diffuse enlargement, which may be subtle.

Peripancreatic fluid is well shown on non-contrast or immediate post-gadolinium gradient-echo images and appears as low-signal-intensity strands of fluid or fluid collections in a background of high-signal-intensity fat. T2-weighted single-shot echo train spin-echo imaging employing fat suppression is the most sensitive technique for showing small volume peripancreatic fluid, which appears as high signal intensity in a background of intermediate- to low-signal intensity pancreas and low-signalintensity fat. As the extent of pancreatitis becomes more severe, the pancreas develops a heterogeneous appearance on pre-contrast T1-weighted fat-suppressed images and enhances in a more heterogeneous, diminished fashion on immediate post-gadolinium images.

Percentage of pancreatic necrosis has been considered an important prognostic indicator in patients with acute pancreatitis. Dynamic gadolinium-enhanced gradientecho images may be useful for this determination. Complications of acute pancreatitis such as hemorrhage, pseudocyst formation, or abscess are clearly shown on MRI.

Hemorrhagic fluid collections are high in signal intensity on T1-weighted fat-suppressed images, and depiction of hemorrhage is superior on MR images compared to CT images.

Simple pseudocysts are low in signal intensity or represented by a signal void in a background of normal signal intensity pancreatic tissue on both non-contrast gradient-echo and T1-weighted fat-suppressed images. Pseudocyst walls enhance minimally on early post-gadolinium images and show progressive intense enhancement on 5 min post-contrast images, consistent with the appearance of fibrous tissue. Simple pseudocysts are relatively homogeneous and high in signal intensity on T2- weighted images.

Pseudocysts complicated by necrotic debris, hemorrhage, or infection, are heterogeneous in signal intensity on T2-weighted images (Saifuddin et al. 1993).



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