Computer tomography (CT) gives information about localization, size and extension of tumor[8,18
], while being non-invasive[32
]. A recent meta-analysis showed CT to be 91% sensitive and 85% specific for tumoral detection[33
]. Phoa et al[34
] showed that, with regard to tumor convexity towards a vessel, Grades D (concave contour of the tumor towards vessel) or E (circumferential involvement of vessel) have a risk of invasion of 88%; and a possibility of resection of 7% for the type D and of 0% for the type E[35
]. Loyer et al[35
] found that Grades A (fat plane separating the tumor from the vessel) and B (normal pancreatic tissue between tumor and vessel) had a resection rate of 95%, therefore these two grades are factors of better prognosis.
On the other hand, the length of tumor contact with the vessel (if it is greater than 5 mm) is a relatively good predictive factor for vascular invasion (78% for portal vein and 81% for superior mesenteric vein)[34
A circumferential contact of more than 180 degrees has been shown to have a good correlation with unresectability[34,36,37
]. For this criterion, Lu et al[38
] found a sensitivity of 84%, a specificity of 98%, a positive predictive value (PPV) of 95%, and a negative predictive value (NPV) of 93%, for unresectability. Furthermore, Phoa et al[34
] reported a sensitivity of 60%, and a specificity of 90%, if tumor convexity Grades D or E were combined with circumferential involvement of > 90 degrees. In addition, a strongly narrowed vessel also has an important risk of being invaded[34,36
], but prudence is essential, especially for a vein, due to the mass effect of the tumor without the presence of vascular invasion[10,39,40
]. In addition, an artery may be completely invaded, with no apparent change in vessel caliber[36,39
Concerning the irregularity of the vascular wall, Li et al[36
] reported a sensitivity and a specificity of 45% and 99%, respectively, for tumor detection in arteries, and 63% and 100% in the case of veins.
Regarding the rare superior mesenteric vein teardrop sign, Hough et al[41
] found a sensitivity of this CT sign of 91% and a specificity of 98%; similar findings were reported in other series[36
Consequently, Li et al[36
] reported that the CT criteria for arterial invasion might be: an arterial embedment in tumor, or the combination of tumor involvement of more than one-half of the circumference of the arteries with artery wall irregularity or with artery stenosis (sensitivity of 79%, specificity of 99%). The criteria for venous invasion might be venous occlusion, tumor involvement of more than one-half of the circumference of the veins, vein wall irregularity, vein caliber stenosis, and teardrop superior mesenteric vein sign (sensitivity of 92%, specificity of 100%).
From the point of view of the detection of vascular invasion, many studies have evaluated CT (Table ). CT has improved much these last years. Technology has developed multi-slice with 4-64 detector rows, allowed thin-sections and dual-phase, with faster time of acquisition, and numerous possibilities of image post-processing (3D reconstructions, multiplanar reconstructions)[19,29,40,42-45
CT performance in the detection of vascular invasion in more than 50 patients with pancreatic cancer
Fourteen years ago, Yoshimi et al[46
] reported one of the first cases of 3D vascular reconstruction, allowing the evaluation of portal invasion with a higher accuracy than angiography alone. Currently, pancreatic section thickness of 1 mm is obtained in approximately 20 s, allowing true volume acquisition, with vascular details better than angiography[28,47,48
] useful when assessing vascular invasion[44
]. Furthermore, CT angiography allows anatomical study of small pancreatic vessels with a remarkable degree of accuracy[49,50
Moreover, dilation of the peri-pancreatic veins with no visualization of inferior branches on CT suggests tumor invasion of peri-pancreatic tissue[50
Several studies have highlighted the importance of the moment of image acquisition. With regard to the pancreas, it seems that a portal venous phase (60 s after intravenous administration of iodinated contrast medium) or that a pancreatic phase (40-70 s) provides more information than an arterial phase (18 s) or that of a hepatic phase (70 to 100 s)[19,29,51-54
]. McNulty et al[51
] reported that an arterial phase can be reserved for patients in whom CT angiography is required.
Lastly, Imbriaco et al[55
] showed that dual-phase helical CT (arterial: 20 s, and pancreatic late: 70 s) was interesting but was comparable with single-phase helical CT (pancreatic early: 50 s).
In conclusion, CT is the assessment of choice in first intention, permitting in one non-invasive examination a TNM staging evaluation.
From the vascular point of view, many criteria exist (especially circumferential involvement of vessel of more than 180 degrees, radiological absence of a fat plane between tumor and vessel, vascular occlusion with collaterals, teardrop sign) which allow accuracy in diagnosing vascular invasion. Development of new radiological techniques (3D reconstructions, multiplanar reconstructions) has improved accuracy of assessment of vascular invasion.