Preoperative diagnosis of pathological PV invasion is of great significance. However, it is difficult to predict PV invasion based on morphological changes alone . Although many reports have proposed various nomograms to predict PV invasion, they are unclear because of subjective evaluation of the CT images . Only morphological measurements with low subjectivity were examined. Significant factors that can predict pathological PV invasion include tumor diameter, length of tumor–PV contact, PV circumference, and PV wall irregularities [9, 10]. However, in this study, neither tumor diameter nor the length of the tumor–PV contact were significant factors in predicting concomitant PVR. This is because the objective variable was not pathological invasion but the presence or absence of concomitant PVR. In some cases with concomitant PVR, the tumor was not in contact with the PV. However, in many cases, concomitant PVR was not required even if the tumor was in contact with the PV. However, in cases with pathological PV invasion, the tumor was in contact with the PV.
Preoperative diagnosis of clinical non-invasion of the PV does not coincide with the need for concomitant PVR. From the data of this study, 35% (15 of 43 cases) had pathological PV invasion among the cases with concomitant PVR (40–60% in other reports) [8, 11]. In other words, in addition to predicting PV invasion preoperatively, it is also important to diagnose whether preoperative concomitant PVR is necessary. There are various concepts regarding surgical procedures. If PV invasion, i.e., PV stenosis or obstruction, is apparent on the CT image, the detachment of that part of the PV should be minimized, and combined resection should be performed. However, if the PV invasion is not apparent on the CT image but still suspected, detachment of the area around the PV may be needed or combined resection if detachment is deemed difficult. On the other hand, if clinical PV invasion is suspected, some surgeons perform concomitant PVR in every case. Even if PV invasion is not clinically suspected, difficulties in detachment around the PV are encountered due to inflammatory and fibrotic changes in the surrounding areas. Therefore, it is also important to determine whether concomitant PVR is necessary before surgery.
It is clear that positive pathological PV invasion is a clear prognostic factor. In cases without pathological PV invasion, there was no significant difference in the incidence of postoperative complications due to concomitant PVR, and the prognosis did not change. Therefore, our surgical policy was considered acceptable. In addition, the determination of the need for concomitant PVR before surgery could enable appropriate surgery preparation. The rate of unexpected PVR may also decrease. Pathological PV invasion could not be predicted using the CT value of the PV used in this study. In other words, there was no change in the CT value of the PV values in the two groups with and without pathological PV invasion (data not shown).
If a black band on the CT image is visible at the border of the pancreas in the closest part of the tumor along the PV, it is presumed that it is a fat layer and the CT value is lowered accordingly. In such cases, it is not necessary to measure the CT value, and it is determined that PVR may not be necessary. On the other hand, PVR can be considered necessary even when the PV is narrowed or obstructed due to obvious cancer invasion in the absence of such a fat layer. Difficult cases showed no further fat layer or any obvious deformation of the PV. In this case, it is speculated that measuring the CT value of the closest part would enable a meaningful determination of the need for concomitant PVR.
In the histopathological findings of this study, the border outside the PV was unclear in cases without pathological PV invasion and with PVR, and hyperplasia of the collagen fibers was observed. These facts provide evidence to support the previous hypothesis. In addition, the notch of the PV in cases without PVR showed hyperplasia of the elastic fibers; however, the arrangement was well-organized and the presence of any outer fat layer was not observed. The possible reason is that the fat layer disappeared during the process of resection and specimen preparation.
The limitations of this study are that the number of cases was small and it was retrospective in nature. In addition, the subjective element in the measurement of the CT value along the PV has not been completely eliminated. The measurement area along the PV and CT values in contrast-enhanced PV imaging has a small range, which makes it more objective but not perfect. Furthermore, the effects of morphological change on the CT value due to the effect of NAC was not examined.