Chronic Pancreatitis

General characteristics

Chronic pancreatitis is defined pathologically by continuous or relapsing inflammation of the organ leading to irreversible morphologic injury and, typically, impairment of function. Chronic pancreatitis is caused by complication of repeated attacks of acute pancreatitis. Alcoholism and obstruction of the pancreatic duct from various causes, including pancreatic ductal cancer, result in chronic pancreatitis.

Imaging

MRI may perform better than CT imaging at detecting changes of chronic pancreatitis, since MRI detects not only morphological findings but also the presence of fibrosis. Fibrosis is shown by diminished signal intensity on T1-weighted fat-suppressed images and diminished heterogeneous enhancement on immediate post-gadolinium gradient-echo images. Most cases of chronic pancreatitis show progressive parenchymal enhancement on 5-min post-contrast images, reflecting the pattern of enhancement of fibrous tissue.

Focal enlargement of the head of the pancreas with chronic pancreatitis may be difficult to distinguish from cancer on CT images.

MR images permit the distinction between these two entities with greater reliability. Both chronic pancreatitis and carcinoma show similar signal intensity changes of the enlarged region of pancreas on non-contrast T1-weighted fat-suppressed and T2-weighted images; generally mildly hypointense on T1- weighted images and heterogenous and mildly hyperintense on T2-weighted images.

On immediate post-gadolinium images, focal pancreatitis shows heterogeneous enhancement with the presence of signal-void cysts and calcifications, without evidence of a marginated definable, minimally enhancing mass lesion. Demonstration of a definable, circumscribed mass lesion is most often diagnostic for tumor.

In chronic pancreatitis, the focally enlarged portion of the pancreas usually shows preservation of a glandular, feathery, or marbled texture similar to that of the remaining pancreas.

In contrast, in pancreatic cancer, the focally enlarged portion of the pancreas loses its usual anatomic detail. Tumor disrupts the underlying architecture and generally exhibits irregular, heterogeneous, diminished enhancement.

Diffuse low signal intensity of the entire pancreas, similar to and including the area of focal enlargement, on T1-weighted fat-suppressed and immediate post-gadolinium SGE images is typical for chronic pancreatitis. In the setting of pancreatic cancer, the enhancement of the tumor is less than adjacent pancreatic parenchyma.

Acute or chronic pancreatitis is well shown on MR images. Pancreatic pseudocysts observed in patients with chronic pancreatitis often arise as a sequel of episodes of acute inflammation (Semelka et al. 1993b). Small pseudocysts and cysts are present and are well shown on gadolinium-enhanced T1-weighted fat suppressed images as nearly signal-void oval structures.