Computed tomography in pancreatic carcinoma

Few pancreatic carcinomas (5-22%) are resectable at the time of diagnosis b ecause this lesion is seldom diagnosed in an early stage. A considerable im provement in the rate of survival is described only for resectable tumors: it is extremely necessary to find an imaging technique for early diagnosis and for accurate staging of pancreatic carcinoma to discern operable from i noperable cancer. The sensitivity of CT in predicting that pancreatic carcinoma is unresectab le has been described as approaching 100%. However the reverse is not true. More than one third of the tumors revealed with CT and interpreted as rese ctable cannot be excised. The major reason for errors with CT are failure t o detected liver metastases, peritoneal implants, lymphnode involvement and encasement of the great vessels by tumor. Significant progress has recentl y been made to improve the detection of these details with the recent intro duction of helical CT with infusion of a bolus of contrast material and thi n section collimation. Traditionally, when a single sequence of images was acquired during abdominal CT, the time of the acquisition was dominated by the requirement to scan during maximal hepatic enhancement, which unfortuna tely may not be optimal for evaluation of the pancreas. With the advent of helical CT, the acquisition of two sets of images after infusion of contras t material is now possible; the first one takes place during the arterial e nhancement; it is useful to detect tumor vascular encasement and the maximu m difference of tissue attenuation between normal greater pancreatic enhanc ement and hypodense pancreatic mass, less vascularizated. It appears that t he peak parenchymal enhancement achieved with helical CT may improve the se nsitivity of CT scanning in detecting pancreatic carcinoma, especially smal l tumors confined within the organ. The second phase takes place during the Venous or portal enhancement and pr ovides useful information about venous encasement and hepatic metastasis. Extraglandular extension with invasion of adjacent major arterial (celiac a xis or its branches, superior mesenteric artery) and Venous (portal, spleni c, superior mesenteric) appear as soft-tissue attenuation thickening obscur ing the perivascular fat, with deformity, thrombosis or occlusion of the ve ssels. In cases-of venous occlusion, collateral vein can be identified. Dil atation of the small veins that surround the head of the pancreas might be used as an additional criterion of extrapancreatic extension of neoplasia. With the features of spiral CT (contrast material optimization and continuo us scanning), the detection of small lesions in the liver and peritoneal im plants has been increased. Helical CT seems not to detect anything else about lymphnode involvement th an conventional CT, limited by the same morphologic criteria. The only CT m eans of detection of node involvement by pancreatic carcinoma is the pathol ogic enlargement of lymph nodes without specificity for neoplastic or not n eoplastic ones. In many cases 2D, 3D and MIP imaging are helpful to evaluate vasculature en casement, especially for visualization of vessels which lie in oblique, cor onal or sagittal plane. Consequently helical CT has the potential to become an alternative angiographic technique. Many studies have been done to evaluate spiral CT potential impact and to c ompare the value of this technique with other ones in the initial diagnosis and staging of pancreatic carcinoma. One of these studies compares dual-ph ase helical CT and endoscopic endo-sonography. The Authors observe that the two techniques do not differ significant statistically in detecting pancre atic carcinoma, except endoscopic sonography is more sensitive than helical CT for tumors smaller than 15-20 mm. They found the accuracy to predict unresectable carcinoma is 100% for dual- phase helical CT and less for endoscopic endosonography (86%). They also af firm that the accuracy for predicting resectability is 90%, similar for end oscopic sonography, but greater than conventional CT whose major limitation is to underestimate the extent of disease.