Although this observational report comprised only seven cases, we found qualitative data, which are summarized as follows:1) 29% (2/7) of PNETs were found to have MVI and 14% (1/7) had a daughter lesion, even though the tumors appeared localized within the pancreas on preoperative imaging; 2) MVI could be adequately evaluated in these cases, even when anatomical pancreatic head resection was performed with DPPHR; and 3) incidence of short-term complications of DPPHR were acceptable, and the incidence of postoperative acute cholangitis, which commonly occurs after PD, was not observed in any of our patients.
At our institution, patients with PNETs limited to the pancreas without obvious lymph node metastasis on preoperative imaging are regarded as good candidates for DPPHR. However, DPPHR is often not indicated if the tumor is adjacent to the bile duct or if the tumor is too large to preserve the arterial arcade in the pancreatic head. Moreover, DPPHR is not indicated for cases in which conventional lymph node dissection is considered necessary based on preoperative CT findings. PD is the only option in such cases.
In the present study, DPPHR was performed in a limited number of cases; however, MVI and daughter lesion were observed in two and one case, respectively. Although it is widely accepted that lymph node metastasis is a poor prognostic factor for PNETs[16, 17], the pathological significance of MVI has not been well clarified. Nevertheless, Yamaguchi et al. [18] reported significantly higher lymph node metastasis in patients with positive MVI, and Kim et al. showed an association between positive MVI and prognosis[19]. Therefore, DPPHR, which allows anatomical resection of total pancreatic head can be considered more relevant for surgical removal of PNETs measuring approximately 2 cm in diameter, compared to enucleation, based on the fact that it facilitates proper evaluation of MVI.
In the present study, neither of the two patients with MVI eventually developed lymph node metastasis. Compared to PD, the extent of lymph node dissection in DPPHR is restricted, however, peripancreatic, peri-GDA, and peri-CHA lymph nodes can be dissected. We believe that even if MVI is detected, additional invasive resection similar to PD is not necessary, unless peripancreatic lymph node metastasis is observed. In addition, the daughter lesion was likely to have been left undetected by enucleation, indicating the importance of anatomical resection of the pancreatic head by DPPHR.
DPPHR preservation of the bile duct is technically challenging, and has not been widely performed in the recent years. Not only the incidence of short-term complications[20], but occurrence of long-term bile duct stenosis is also a concern[21, 22]. However, Kato et al. compared the incidence of short-term complications in patients with low-grade malignant tumors treated with DPPHR and PD, and reported no difference in the incidence of short-term complications such as pancreatic fistula. Moreover, they also reported a significantly lower incidence of postoperative cholangitis in the long term [11]. Horiguchi et al. also reported that postoperative endocrine and exocrine functions were significantly preserved in the DPPHR group compared to the PD group[7]. Therefore, DPPHR may contribute to improving the postoperative quality of life of patients with PNETs. However, since this was a retrospective study with a very small number of patients, further accumulation of cases and long-term follow-up, including prognosis, are needed.