Retroperitoneoscopic surgery must be performed in a narrow operative space and is thus said to be technically difficult to perform, and therefore laparoscopic surgery was recommended in the past . However, the invention of atraumatic balloon dilation has made it easier to secure a space , and retroperitoneoscopic surgery has been in widespread use in recent years . Many reports have presented results of a comparison of retroperitoneoscopic surgery with open surgery and laparoscopic surgery, and the studies concluded that retroperitoneoscopic radical nephrectomy is in no way inferior to other traditional surgical methods [9, 10]. It is certain that there have been significant technical improvements in retroperitoneoscopic surgery. At the same time, there are also reports on the existence of learning curves . Tobias-Machado M et. al.  reported that a clear learning curve was obtained in the initial 15 cases.
Inderbir S. Gill et. al.  compared the outcomes of a laparoscopic partial nephrectomy for renal cell carcinoma soon after introducing it into their institution with the outcomes of an open laparoscopic partial nephrectomy for renal cell carcinoma, and reported that the incidence of intraoperative complications was significantly higher in laparoscopic surgery. This indicates that laparoscopic partial nephrectomy for renal cell carcinoma is technically difficult to perform. Furtheremore, however laparoscopic surgery is said to be safer, that may also induce complications. The complications tend to be occurred particularly when laparoscopic surgery is performed during the introduction period when surgeons and medical staff are still unfamiliar with this surgical method and when learning curves have not yet been determined.
Safer laparoscopic surgical methods, such as hand-assisted laparoscopic surgery, have now been devised  and it has been proved that these methods are less invasive than open surgery. The A method was similar to this hand-assisted laparoscopic surgery. But the A method could be better than hond-assited method in terms of being able to using abdominal air pressure to prevent bleedeing. The A method was performed at the time of introduction of retroperitoneoscopic surgery into our institution and it was possible to obtain stable results.
One of the advantages of the A method could be safety. Since it is possible to remove the flank pad and to access the retroperitoneal space under one's direct vision, it is easier to understand the orientation, and it is possible to more promptly facilitate open conversion in cases of massive bleeding. However, the open conversion in 1 case of the A method was not emergent but selective. So, we were fortunately not given an opportunity to perform it in order to stop massive bleeding.
On the other hand, one of the disadvantages of the A method is larger size of the incision. The incision, which is about 7 cm, is larger than the approximately 5 cm incision in the traditional methods, and the preceding incision limits port sites. In particular, limits of port sites were more prominent with thinner patients and disturbed the surgical procedures in quite a few cases.
In this study, there was no difference in surgical outcomes between the A method and the B method for renal cell carcinoma. Since there was no difference in the outcomes between the A method at the time of introduction of retroperitoneoscopic surgery and the B method when the staff had become familiar with retroperitoneoscopic surgery, it was indicated that the A method could be safer. In addition, we had to state that we have limitations in this study because of small sample size included. Such a small number of sample included in this study might be related to a lack of statistical power. That could induce no difference between the two groups in surgical outcomes.