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.