Intraductal papillary mucinous neoplasm of the pancreas: differentiate from chronic pancreatits by MR imaging.

PURPOSE: To evaluate the differentiating factors for intraductal papillary mucinous neoplasm of the pancreas and chronic pancreatitis as determined by MR imaging.

MATERIALS AND METHODS: During a three-year period, we performed MR imaging on 33, consecutive patients with IPMN and on 41 patients with chronic pancreatitis. All IPMNs were confirmed by surgery. Two radiologists retrospectively analyzed the ductal change, the cyst shape, CBD dilatation, lymphadenopathy, and parenchymal change. The sensitivity and specificity were calculated for each MRI findings using the Chi square test. Statistically significant MR findings were further analyzed using multivariate logistic regression analysis. The diagnostic performance was evaluated according to the area under the receiver operating characteristic curve (A(z)) using specific MRI findings. Simple κ statistics were used to evaluate the inter-observer reliability.

RESULTS: Statistically specific findings for IPMN compared with those for chronic pancreatitis, were duct dilatation without stricture (specificity=95.1%, sensitivity=75.8%, p<0.0001), bulging ampulla (specificity=97.6%, sensitivity=30.3%, p<0.0001), nodule in a duct (specificity=100%, sensitivity=15.2%, p<0.0004), grape-like cyst shape (specificity=97.6%, sensitivity=78.8%, p<0.0001), and nodule in a cyst (specificity=100%, sensitivity=24.2%, p<0.0001). Statistically specific findings for chronic pancreatitis compared with those for IPMN, were duct dilatation with strictures (specificity=93.9%, sensitivity=95.1%, p<0.0001), the presence of a stone (specificity=97.0%, sensitivity=56.1%, p<0.0001), and a unilocular cyst shape (specificity=93.9%, sensitivity=34.1%, p<0.0004). Duct dilatation without stricture and a grape-like cyst shape were independently associated with the IPMN. Duct dilatation with strictures was independently associated with the chronic pancreatitis. Interobserver agreement was good to excellent for each finding (κ=0.762-1.000).

CONCLUSION: Highly specific findings for IPMN include duct dilatation without stricture, bulging ampulla, nodule in a duct, grape-like cyst shape, and nodule in a cyst. MRI is very useful for differentiating IPMN from chronic pancreatitis using these specific findings.