MRI of the pancreas: tumours and tumour-simulating processes

Abstract

The most important issues in pancreatic imaging are the detection and staging of pancreatic cancer, differentiation between cancer and focal pancreatitis, the characterization of cystic lesions and the search for neuroendocrine tumours. Magnetic resonance (MR) units (1.5 T) with strong gradients and a phased-array torso coil should be used, making breath-hold imaging possible in order to avoid motion artifacts. Standard imaging sequences are T1-weighted (T1w) gradient recalled-echo (GRE) with and without fat saturation. For T2-weighted (T2w) imaging, axial single-shot turbo spin-echo (TSE) and coronal/oblique MR cholangio-pancreatography (MRCP) pulse sequences are preferable. As contrast agents either gadolinium agents or mangafodipir trisodium are used. Dynamic gadolinium-enhanced T1w fatsat 3D GRE images are helpful to delineate vessel infiltration by adenocarcinoma and to assess the aetiology of cystic masses. Mangafodipir-enhanced MRI has been found to be superior to helical computed tomography (CT) in the detection of small cancers and in the delineation of liver metastases. In cases of an equivocal pancreatic mass the presence of the "duct penetrating sign" at MRCP (i.e., the duct traversing the mass) is suggestive of an inflammatory pseudotumour. Hypoattenuation due to focal fatty infiltration may mimic a tumour at CT, but in-phase and opposedphased T1w imaging readily depicts the fat. Multi-detector CT has gained increasing popularity for pancreatic imaging because of the 3D visualization of the peripancreatic vessels. However, MR imaging is excellent in the delineation of small pancreatic tumours. Due to its superior soft tissue contrast, MR imaging is also the method of choice in the differential diagnosis between tumours and tumour-simulating conditions in patients with equivocal CT and to assess cystic lesions.

Comparison between multislice CT and MR imaging in the diagnostic evaluation of patients with pancreatic masses

“…Finally, in one patient with focal chronic pancreatitis, both CT and MR imaging were false positive for malignancy. However, it is well known that pancreatic enlargement and contour disruption typical of focal chronic pancreatitis can mimic malignant disease [25]. Despite these erroneous results of both CT and MR imaging, statistical analysis did not reveal statistically significant differences between modalities in identifying or evaluating resectability of malignant masses, so we may hypothesise that either technique can be used in these patients, depending on availability.…”

Role of Endoscopic Ultrasonography in Patients Suspected of Pancreatic Cancer with Negative Helical MDCT Scan

“…The value of an additional MRI (or MRCP) in patients with obstructive jaundice without a suspected mass or other cause of obstruction requires further investigation, since the overall detection rate for pancreatic carcinoma is comparable to MDCT [20,21,22]. MDCT is superior to MRI in the assessment of locoregional extension of pancreatic carcinomas, since 3D reformations are excellent to delineate arterial or venous encasement [23,24]. The superior tissue contrast of MRI makes it favorable for the definition of cysts and septations, but suspected benign causes of obstruction preferably need confirmation with cytology or histology.…”

The Status of Neuroendocrine Tumor Imaging: From Darkness to Light?

“…MRI is particularly advantageous in localizing primary pancreatic tumors and for staging and restaging liver lesions [37]. Moreover, cholangiopancreatic sequences (magnetic resonance cholangiopancreatography), directed at studying the involvement of the biliary and pancreatic ducts, are useful for surgical planning and should always precede resection of a pancreatic NET [8,41]. …”