[MR imaging of pancreatic neoplasms]

The role of MR imaging in the assessment of pancreatic adenocarcinoma is in identification, characterization and staging of the neoplastic lesion. Technique optimization is required in order to obtain high qualities images competitive with spiral CT. The choice of imaging protocol is strictly related to the available equipment as well as fast imaging capabilities. Contrast-enhanced study using breath-hold sequences is required if working at high field strength with high gradient performance; on mid-low field strength nonbreath-hold acquisition techniques, using respiratory compensation techniques, can be implemented. The use of fat saturation pulses may increase the sensitivity of MR in detecting pancreatic lesions. Other advantages of MR imaging are represented by the availability of additional noninvasive techniques for the evaluation of the biliary tree (MR-cholangiopancreatography) and splanchnic vessels (MR-angiography). Lesion identification is based on TIw sequences where the lesion appears hypointense compared with the surrounding pancreas; increased lesion-pancreas contrast is obtained when fat suppression is used. On dynamic studies following gadolinium injection, pancreatic tumors are hypovascular compared with surrounding normal pancreatic gland. Problems in correctly defining the size of the lesions may be encountered in patients presenting with inflammatory changes of the pancreatic parenchyma surrounding the carcinoma (epineoplastic pancreatitis). For lesion characterization MRI is not able to characterize focal pancreatic lesions, allowing a differential diagnosis between pancreatic cancer and focal hypertrophic chronic pancreatitis. Even the use of MR-cholangiopancreatography is not helpful for characterizing focal pancreatic masses. MR imaging is accurate in local staging (assessment of peripancreatic fat infiltration) thanks to the higher contrast resolution, but in vascular staging and in the evaluation of lymphnodal involvement it suffers the same limitations as computed tomography. Future perspective are represented by the use of magnetic resonance angiography for the evaluation of vascular encasement and the use of specific contrast agents for lymphadenopathy. Identification of hepatic metastases with MRI has been proven to be high, with sensitivity and specificity comparable to CT. The use of liver-specific contrast agents (either positive or negative) is becoming almost routine and it is proving to further improve the diagnostic value of MRI.