PCNL has been recommend as the first-line treatment for intrarenal stones larger than 2 cm according to European Association of Urology Guidelines. Although the advantage of high stone clearance rates has been widely proved in reports, the invasive method with serious complications might also worry urologists inevitably. At the same time, RIRS has been recommend as the first-line treatment targeting intrarenal stones between 1-2 cm, in particular, for patients of obesity, anticoagulation, skeletal deformity and renal anomalies, the indications of RIRS could be broaden[12-14,11].
Several studies have already attempted to employ the RIRS to treat the stone>2 cm and exhibiting some positive effects. However, in spite of these positive results, RIRS is still considered escalating the treatment cost and requires multiple sessions to clear large stone >2 cm in current strategy, long surgery time and several sessions also might lead serious complications such as stricture and fibrosis of ureter, it has been proved that the elevated levels of renal injury biomarker increase further according to stone size and surgery time， which means larger stone and longer surgery time would raise the risk of renal injury positively [16,17], whereas PCNL provides a SFR around 95% but with potential invasive complications after the first treatment [18-20]. The optimal surgery decisions for 2-3 cm stone become a topic worth pondering and need to be elucidated.
HU value of NNCT for kidney stone usually used for ESWL preparing. The stone density has been reported to relate to ESWL outcome, Stones ≥ 1000 HU are less likely to be disintegrated[21,22]. However, urologists usually focus on this indicator in ESWL but likely to neglect it before lithotripsy. No studies focused on the outcomes of large stones (>2 cm) performed by RIRS with HU value evaluated so far to our knowledge. In our clinical experiences, the stone density < 1000HU could be easily fragmenting initially and then dusting to suitable size particles by adjust holmium laser settings using RIRS, except the stone of low calyx or severe hydronephrosis, which might be more suitable to perform PCNL or mPCNL from treatment or cost effectiveness. For the stones >1000HU, some cases might need a long time and not easy to dusting. New high-tech Ho-YAG laser might be utilized and considered great efficiency to all HU value and chemical composition stones, however, some studies confirmed our experiences and presented that the lower efficiency of holmium laser in some stone cases . Moreover, lasers in undeveloped area might not work well in all stones, especially for large stones, which need a long surgery time and easily cause complications.
Even with high-tech laser, residual stone could not be avoided in all cases probably. Due to existed controversy and limited literature, we reasoned that it would be meaningful to conduct this small prospective single-center studies to define the potential decision aid of screening the HU value on 2-3 cm renal calculus to perform RIRS or PCNL and following outcomes.
The highlight of our present study, is that we firstly proposed HU value should be taken as a routine consideration in 2-3 cm stone diseases requiring RIRS or PCNL surgery which might change the surgery decision in some cases. The threshold of 1000 HU is widely accepted in ESWL procedure. It might not be accurate but really effective in preparation of RIRS. Larger renal stones needed a significantly longer operation time, which essentially increased the risk of sepsis, especially in RIRS. Without prompt management, sepsis would be dangerous and even life-threatening. Stiff stones > 2 cm with high density might not fit for RIRS and could be easily performed by PCNL. Fragile stones (postulate HU<1000HU) might be the optimal candidate for RIRS and might benefit patients. Adjuvant ESWL would be also meaningful and efficacious to the residual stones less than 1000 HU if necessary. The second session RIRS or PCNL might be omitted. During our preliminary study, some cases of easily disintegrated stones were noticed and marked, which mostly proved HU<1000 HU. Therefore, we organized four groups to assess if 1000 HU value might be useful in RIRS or PCNL. The results exhibited that with consideration of HU value, no severe complications and repeat session were noted in RIRS group and adjuvant ESWL were all efficiency. The surgery time, hospital stay and complications of RIRS after HU value evaluated were superior to cRIRS and two PCNL groups.
Our results confirmed that PCNL offered a higher SFR than RIRS as well, which was consistent with most published studies [8,20,2]. Zewu et al supposed that the potential reasons for RIRS with a relatively lower SFR may be due to residual fragments that are more likely to represent a cluster of clinically insignificant fragments and small working channel according literatures, as well as a call for the vacuum aspiration stone system for RIRS. However, RIRS with HU value evaluated could provide a comparable final SFR and shorter recovery time with fewer overall complications for intermediate-size renal stones (2-3 cm) in one session with help of adjuvant ESWL in many cases. During our follow-up, best overcomes raised from patients of RIRS with HU value evaluated, none received a second session RIRS and ureteral stricture or other severe complications.
There were several limitations need to be taken into account when considering the present work. Firstly, timing of the outcome evaluation and follow-up might not long enough. Some residual stone fragments may pass away in 6-12 months after surgery, the 3 months’ endpoint seems not enough and may overestimate our failure rate. Secondly, among the present patients, all RIRS group with a stone density of < 1000 HU and had no complications in 3 month follow-up. This result indicated that 1000 HU value played a critical role in predicting the successful of RIRS and exclude those might suffer a poor outcome or complications. The fact we need to know, is that these patients initially decided to perform RIRS properly and then following set groups by HU value were evaluated. Some cases of cRIRS group were still >1000 HU and proved that RIRS were remain an efficacious management. The threshold, comprehensive indicators and networks approach may need further investigated. Third limitation is the consistency of stone fragility and HU value. For most cases, HU value could offer a predictive and corresponding information before surgery. However, as to pure cystine stones with HU<1000 and account for less than 2% of all cases of lithiasis, might not be easily fragmented and dusted by employing RIRS if stones are larger than 2 cm. Therefore, for the small group of patients with family calculus history, young age and metabolic abnormality, more attention before surgery is needed. Lastly, the limitation is participant size, we tried to identify and enroll as many patients into the trials for last three years. However, it might not easy for a single-center to conduct an ideal participants’ size of particular range stones (2-3 cm) for analysis though the total number of stones’ surgery at our center was high (>800 cases/year). Given the large sample numbers and long follow-up periods, it seems likely study of this magnitude might probably miss follow-up data and generate bias. A multiple center study therefore needed.
After all, it is important to balance benefits and risks according to the characteristics of individuals and select an ideal treatment for patients. Our study further supports RIRS as a safe and efficacious treatment option for renal stones of 2-3 cm in size if HU value has been considered for evaluation. A number of patients thus might not have to suffer the potential severe complications of PCNL. Although both the EAU and AUA guidelines do not currently recommend RIRS as the first-line treatment of 2-3cm stones, we indeed have confidence to utilize as primary modality if patients are properly selected. Nevertheless, further prospective randomized multi-center trials are required to confirm these results.