الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Imaging of the pancreas is a challenging entity due to a large number of primary pancreatic neoplasms, as well as benign entities of the pancreas that simulate neoplasms, such as inflammatory and cystic disease. While clinical and laboratory data are able to distinguish many of the disease processes affecting the pancreas, imaging is inevitably tied to diagnosis and treatment, given the significant overlap of patient symptoms in benign and malignant pancreatic disorders 155. The goal of pancreatic imaging is the early detection and characterization of clinically relevant pancreatic lesions. Unfortunately, incidental cystic pancreatic lesions detected by multi-detector computed tomography (MDCT) are increasingly common and can range from benign incidental lesions to malignant. The resection of all cystic lesions is impractical, as a significant proportion of these lesions are benign 155.
Transabdominal US is the first imaging method used in the assessment of abdominal pain and abdominal emergencies. Non-invasive and nonradiating, it is easily accepted by patients and has proven to be a very good diagnostic tool if performed by an expert. Lately, it has been used as an extension of the clinical examination, shortening the diagnostic time. The disadvantages of this technique are the difficulty of a complete examination in overweight patients, operator dependence, and low reproducibility. The limits of transabdominal US in the diagnosis of pancreatic diseases are in case of tumors <10 mm diameter and in the assessment of the necrotic and ischemic areas in acute pancreatitis, even when harmonic techniques are used. The use of contrast agents has further improved the diagnostic accuracy 176. Contrast-enhanced ultrasonography of the pancreas represents a new development of conventional ultrasonography. Its main indications are the assessment of the solid tumors according to the enhancement pattern following the contrast agent injection, and the differential diagnosis between pseudotumoral chronic pancreatitis and pancreatic adenocarcinoma. The technique might improve the tumor staging by a more precise delineation of the resection margins. The neuroendocrine tumors pattern after contrast administration is highly characteristic, increasing the diagnostic accuracy. In acute pancreatitis the method is useful for the identification of necrotic areas and for the differentiation of pancreatic pseudocysts from cystic neoplasms by evidencing the vascularized septa 176.
CT is the initial imaging test most commonly performed when abnormalities of the pancreas are clinically suspected. Its high sensitivity and specificity for pancreatic disease and non-invasive nature make it a good screening test for malignancy, and it can often assist the radiologist in diagnosing benign pancreatic disease 155. CT studies address the detection and characterization of pancreatic tumors, as well as the predictive value of CT for resectability. The most significant problems affecting radiologic imaging and CT in general, are again in the detection of micrometastatic disease to liver and peritoneum, as well as in the underestimation of vascular invasion 177. MRI is typically used as a problem-solving modality, for example, when a pancreatic mass is suspected, but not identified on MDCT. It should also be considered an excellent imaging study in patients with an iodinated contrast allergy 155. Generally, imaging principles of MDCT translate over to MRI, including principles of contrast enhancement (hypervascular versus hypovascular) and spatial resolution. MRI has increased tissue contrast resolution over CT, which is its primary imaging advantage 155.
MRCP can directly image the duct and has the advantage of being noninvasive, faster, and more readily available than ERCP. In addition, MRCP can be helpful in directing ERCP-guided therapy when ductal anomalies are present, such as pancreas divisum 81. MRI with MRCP accurately depicts the morphologic features of the cyst and has the advantage of demonstrating the relationship of the cyst to the pancreatic duct 178. EUS clearly has a role in current diagnosis and staging of pancreatic abnormalities. EUS and MDCT appear to be similar for assessing local extension and tumor respectability, and in detecting nodal disease. An additional advantage of EUS is that fine needle aspiration can be performed at the time of study 155.
EUS is superior to MDCT in the detection of pancreatic lesions less than 2 to 3 mm, with a sensitivity of > 90 percent for lesions with this size 179. Given the high sensitivity for small lesions, EUS can be performed if the CT shows a focal abnormality without a clear mass or if ductal signs suggest an infiltrative process and there is a suspicion for chronic pancreatitis 180.