MRI is an imaging method useful in screening high risk patients for pancreatic cancer
Screening the High-Risk Pancreas
Pancreatic cancer (PC) is the 4th leading cause of cancer-related death in Western countries (1), with a 5-year survival rate of less than 5% (2). Risk factors for PC can be subdivided in non-hereditary and hereditary: in the non-hereditary conditions (tobacco smoke, obesity, type 1 and 2 diabetes, chronic pancreatitis) only for chronic pancreatitis the associated risk justify the screening. However, there are some cystic tumors of the pancreas (IPMN, MCN) which are considered as at high risk of malignant transformation, thus these patients usually undergo surgical resection in case of high risk or screening for malignant transformation in case of low risk (3). Moreover, some hereditary conditions can be considered associated with an increased risk of PC: a strong family history of PC, called familial pancreatic cancer (FPC), and genetic syndromes associated with an increased risk of pancreatic cancer. There is a familial aggregation of pancreatic cancer: the relative risk ranges from 4.5-fold in case of a single affected first-degree relative to 32-fold if 3 or more first-degree relatives are affected (4). An individual can be considered at risk if there are at least two first-degree relatives affected by PC, or if three or more relatives are affected regardless of the degree of relationship and should undergo screening (5). Many genetic conditions are associated with an increased risk of PC: Peutz Jeghers syndrome, Hereditary pancreatitis, Familial atypical multiple mole melanoma, Breast and ovarian cancer syndrome, Cystic Fibrosis, Hereditary non-polyposis colon cancer and Familial adenomatous polyposis. The relative risk is variable in the different conditions, however in the first 3 groups the risk is increased from 34 to 132 folds (1). Primary prevention of PC is unfeasible as the cost/benefit of total pancreatectomy (the actually only available solution) is not recommended (1). Thus screening is actually the only possible solution in order to identify PC in its early stage, the only which can give some possibilities of long term survival (6). EUS has been proposed as a screening tool, with high accuracy in this group of patients (1), however due to its moderate invasiveness and limited availability, other less invasive and widely available imaging methods have been proposed. MDCT has limited application in this group of patients, due to the use of radiation in relatively young persons and the use of iodinated contrast media, which is necessary in order of identify small pancreatic lesions. MRI with state of the art imaging with multi-channel phased-array coils and parallel imaging acquisitions, 3D gradient-echo sequence for dynamic multi-phase postcontrast imaging as well as 3D MRCP have allowed for increased spatial and contrast resolution, as well as decreased artifacts, with resultant improved visualization of the pancreas. Lack of invasiveness and ionizing radiation, a naturally high contrast resolution which makes the use of paramagnetic contrast agent not necessary give opportunity to develop a fast assessment of the pancreas. In a recent study the sensitivity of MRI for detection of SPL per was significantly higher than that of CT, and MRI provided better lesion conspicuity than MDCT (7). Moreover, with its superior contrast resolution, MRI has been shown to more reliably detect smaller, noncontour-deforming tumors compared to CT (8). Also in the detection of small pancreatic cystic lesions (sPCL), which can be represented also by preneoplastic conditions (Mucinous Cystic Neoplasms, IPMN), MRI enables more confident assessment of the morphology of sPCL than MDCT (9). A complete workup of the pancreas with MRI requires a T2w assessment of the pancreatic parenchyma, a T1 with fat saturation, DWI with at least 3 b values (50-400-800), 2D or 3D MRCP and a gadolinium-enhanced 3D GRE multiphase acquisition. However, in the scope of screening, the main issue is to have a fast assessment of the pancreas with a high negative predictive value, leaving to a more complete workup only in case of suspicious pancreatic lesion. The role of the different sequences, their improvement with new technical advances, such as compressed sensing (10) and simultaneous multislice techniques (11) as well as clinical indications will be discussed in this presentation.
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