Discussion
In recent years, flexible ureteroscopy has become more minimally invasive, effective and safe endoscopic surgery for upper urinary tract calculi and renal stone. FURSL has been performed at many hospitals worldwide due to the acceptable SFR and limited invasiveness, and it was recommended by European Association of Urology as the first choice for the removal of renal stone <2cm and alternative method for the removal of stone >2cm in patients with contraindications for PCNL[1]. Advances in technologies such as the development of new flexible ureteroscopes and small diameter effective lasers have made FURSL an efficient and safe option to manage urinary stones[12].At present, flexible ureteroscopy is used widely, but there are still some clinical problems to be solved.
Before the operation, the characteristics of stone (size, number, density, location) and morphological structure of renal collecting system should be considered first. In our study, we evaluated the characteristics of stones and the structure of collecting system preoperatively through non contract CT examination and intravenous urography of urinary system and excluded the patients who were not suitable for FURSL. We focused on the influence of stone size, burden and location on FURSL. According to the guideline, ESWL and FURSL are the first-line treatment for the stone of non renal lower calyx less than 2cm, and for the renal stone larger than 2cm, PCNL is the first-line treatment. Our present study showed that the overall effect of treatment in <2cm stone group is superior to it in > 2cm stone group. Also for the patients with high stone burden, FURSL would prolong the operation time and increase the risk of surgery. In our study, we adjusted the holmium laser parameters during the operation according to the density and burden of stones. For the patients with high stone density and burden, we usually used high-energy and low-frequency to make the stone fragment first, then we used high-frequency and low-energy to make the fragmental stone dust. Many studies[13-15] have showed that for the less than 2cm renal stones, the post-operative stone-free rate of RIRS was higher and re-treatment rate was lower, and the complications were not increased significantly. For the patients with >2cm renal stone, the study[11] also have showed that FURSL can successfully treat patients with a high stone-free rate and a low complication rate, and with an average of 1.6 procedure per patient, which could be an alternative therapy to PCNL. In our study, majority of patients with stones less than 2cm, which is related to our preoperative selection of patients, for large stones, we need to further study to confirm its effectiveness and safety.
The location of stone is another important aspect that we need to consider. At present, the treatment of renal lower calyx stones is still challenging and the techniques of FURSL, ESWL and PCNL have their own advantages and disadvantages. For renal lower calyx stones, PCNL has a high stone free rate, but the incidence of complications is high, such as bleeding, long post-operative hospital stay. The main advantage of ESWL is non-invasive and convenience, however the main disadvantage of it is low stone free rate and high incidence of retreatment, especially for renal lower calyx stone. Base on higher SFR and fewer complications of FURSL, more and more patients with renal stone take it as the first choice of treatment. As we know, infundibulopelvic angle (IPA) is the most important factor in the FURSL procedure, when the IPA<30°,the success rate of operation and stone free rate will decrease significantly in renal lower calyx stones[16]. Guven[17] reported that in their 1112 patients, residual stones in 276 cases (24.8%) following the first RIRS session; out of these, 121 patients (39.4%) required a second active intervention. Residual fragments were on average 8.36 mm and were located in the lower pole calyces (55%) of the treated kidney. In our study, the effect of FURSL in the treatment of non-renal lower calyx stone was also better than that of renal lower calyx stone significantly. For renal lower calyx stones, we usually moved the stones to the upper and middle calyces by the basket and then the stones were broken by holmium laser. However in the our patients with renal lower calyx stone, when IPA<30°,the stone was difficult to move and break, which result in the stone free rate is decreased significantly.
Stent placement before FURSL can theoretically expand the ureter to improve access and remove stones. Even if current guidences[18] suggest that routine stenting before ureteroscopic procedure is not necessary, several studies[19] have showed preoperative stenting improves the stone free rate, reduces intra-operative complications and facilitates the placement of uretaral access sheaths. In our study, stent placement was underwent regularlly before operation in most of the patients, which increased the success rate of the FURSL procedure. In recent years, with the increasing experience, there are some patients in our unit, especially female patients who did not place stent before operation. Our present sudy have showed that the preoperative ureteral stenting had no significant effect on operative outcomes or complications such as SFR, operative times and perioperative complications, which is similar to previous study[20].
In this study, hematuria, fever and low back pain were the most common postoperative complications. Among these patients, septic shock and subcapsular hematoma ocurred in five patients respectively, and no serious complications were occurred such as ureteral degloving and rupture. We analyzed that it is related to the long operative time, high stone burden and the patients, own condition. All these patients were cured after active treatment. In a prospective study of multiple centers[21], the overall incidence of postoperative complications was 3.5%(416/11885), most of which were Clavien-Dindo grade I or II. Only 0.2% of the patients needed blood transfusion and five patients died within 30 days after operation, and the readmission rate within 3 months after operation was 8.4%. Most of the patients were mainly due to mild abdominal pain and discomfort of ureteral stent. Cindolo [22] first described six cases of mortality after FURSL. Later on, they analyzed outcomes of 12 patients with major complications after FURSL. Eight patients developed a renal injury, one an arteriovenous fistula, two a ureter avulsion, and one acute sepsis; artery embolization and surgical repair were successful in six patients whereas the other half underwent open nephrectomy[23]. In our study, all patients with the serious complications were cured after active treatment and no patients were died due to the FURSL. Therefore, we believe that FURSL is a safe treatment for the upper urinary tract calculi.
However, the main limitation of FURSL is represented by treatment resulting in residual small fragments that may prompt subsequent stone events. The purpose of the procedure is remove the stone completely, but the stone free rate can not reach 100%. Different laser setting can lead to stone dusting and fragmentation. The dusting technique require low energy and high frequency to make the stone to tiny fragment sizes that can pass spontaneously.On the contrary, high energy and loe frequency can result in fragments which can be extracted by endoscopic baskets. El-Nahas[24] retrospectively reviewed outcomes of 107 consecutive patients undergoing FURSL using either the dusting (N=51) or the fragmentation and retrieval techniques (N=56). Both techniques showed comparable safety, hospital stay and requirement for secondary procedures but the dusting technique had a significantly shorter operation time while the fragmentation and retrieval technique had a significantly better SFR. In our study, we use the technique of dusting and fragment, the fragments could be removed by the baskets and the dusting would pass out of the body spontaneously. During the follow-up, the effect of stone removal was satisfactory and most of the patients obtained the good therapeutic effect. However we also observed that about one fourth of the patients had residual stones less than 4mm, and according to our criterion, we think it as meaningless stone. The previous study[25] shows that among patients with post-ureteroscopic renal stone fragments <4 mm, approximately one in five (or 19.6%) will experience a stone event over the following 1.6 years. The remaining patients will either become stone-free via spontaneous passage or retain asymptomatic stable-sized fragments. Thus meaningless stone does not represent no stone, no matter how small the stone is, there is a certain risk. The current study[26] show that the SFRs at postoperative day 1,30 in suctioning UAS group are higher than it in the traditional UAS group. We look forward to there may be more ways to remove stones in the future.