Currently, percutaneous nephrolithotomy (PCNL) remains the mainstay of treatment of all type of renal calculi, with high a success rate and stone-free rate (SFR). The complication rate was notably low in this PCNL procedures compared with another procedure to treat any kind of renal stones. Thus, in the past few decades, nearly all open surgery for treating renal stones, whether simple stones or complex staghorn stones, have been changed to this minimally invasive procedure ¹ .

For complex renal stones and staghorn stones, PCNL is the preferred surgical modality ² . Modifications to the original technique aimed to increase both efficacy and safety of PCNL procedures to treat patients with large and complex renal stones. There are three approaches to perform PCNL for renal stones: lower pole (LP) access, middle pole (MP) access and upper pole (UP) access. The traditional LP access has been proved as the safest approach for renal collecting system access, with a lower risk of bleeding and other thorax-related complications (either hydrothorax or pneumothorax) ³ . However, on the other hand, this LP approach may not be sufficient for complete stone clearance in patients with complex or staghorn renal stones as well as proximal ureteral stones ^{4, 5} . Due to this reason, UP access is advocated as the preferred PCNL approach for complex and staghorn renal stones. PCNL with UP access is considered to allow a higher stone-free rate due to its direct access to the intrarenal collecting system, fewer punctures and less manipulative trauma compared to LP access. However, this UP approach has a notable deficiency. UP access is believed to be associated with a higher complication rate, which is mainly related to thoracic and abdominal complications, particularly when the puncture is done above the 11 ^th rib. We designed this meta-analysis to systematically describe the outcomes and complications of PCNL for staghorn stones in upper and non-upper pole (lower and middle) approach.

Three prospective and two retrospective comparative studies involving 384 renal units with staghorn stones ( Figure 1 contains a flow diagram), with 176 cases done using the UP approach and the other 208 cases using either lower or middle pole approaches. In this present time there was no randomized controlled study that comparing upper and lower pole approach PCNL for staghorn stone. Study characteristics are shown in Table 2.

For patients with staghorn renal calculi, PCNL is the preferred modality of treatment. A successful PCNL procedure requires optimal placement of the percutaneous renal access, thus providing good access for intrarenal stone clearance procedure ¹¹ . Currently UP access and LP access are the two favored approaches to performed PCNL in patients with staghorn calculi ² . The current consensus among endourologist is that a prone position PCNL procedure, which done through posterior calyx approach, will give highly limited access to the upper calyx. Because of this reason, upper calyx approach was the preferred procedure to treat large and complex staghorn stones. Upper calyx access provides direct access down to most renal calyxes and the ureter, and most of middle calyces can be accessed with the UP calyx approach, with the usage of flexible nephroscope. Previous literature show that the usage of UP calyx approach in patients with staghorn renal calculi will result in satisfying SFRs, less access punctures in PCNL, and less renal tissue trauma due to minimal intrarenal manipulation compared to LP access ^{7, 12– 14} . Mostly, the UP calyx approach is done in a supracostal fashion, which results in markedly higher rates of thoracic and other complication, such as pneumothorax and hydrothorax as well as higher risk of bleeding, especially with punctures access that made above the 11 ^th rib ^{7, 12– 20} . However, despite the high risk of complications explained above, evidence suggests the use of the UP approach, as the higher SFR and better access to multiple calyces overshadows the drawbacks of this procedure ^{7, 14, 21} . Nevertheless, this approach should be limited to cases when there is no other available alternative. Performing LP access maybe result in decreased risk of complications, but a complete stone-free condition in some complex upper calyx calculi is limited because of limitations to the LP approach of upper calyx access ²² .

To completely eliminate calculi with PCNL, good access is mandatory. Ideally, PCNL access tract should provide the shortest and most straight access to mostly of the renal stones. Calculi in a single inferior calyx can be easily removed through a single LP calyx access tract. However, for complex and staghorn calculi occupying several calices in the lower pole, access through the superior calyx is thought to be beneficial ¹⁰ . In the present meta-analysis, of 5 studies involving 384 renal units, we did not find a significant difference in SFRs between these approaches, with SFRs of 74.4% for the UP approach and 71.1% for the NP approach (OR: 1.55; 95% CI: 0.92-2.63; P=0.10). This suggests that in staghorn calculi patients, SFRs for the UP access approach is similar to those for the NP access approach. This result is probably different from other studies ^{12, 13} , maybe because we analyzed single access PCNL in patients with staghorn calculi only, while the majority of other studies rarely analyzed staghorn stone or single access PCNL alone. The advantage of UP access is its naturally direct access to the intrarenal collecting system and to the upper ureter ²³ . Because of the linear position of the upper pole with the ureteropelvic junction, intraoperatively the PCNL wire will enter into ureter in the majority of cases. Excellent visualization of the superior calyx, pelvis, and the anterior and posterior inferior calyces of the kidney will be provided by the straight tract along the long axis of the kidney. This condition will make it easier to move and manipulate the nephroscope and forceps thus will reduces the possibility of intraoperative bleeding ¹¹ . PCNL access through UP calyx is one of the most important way of ensuring better renal calculi clearance. This access can be done with either supracostal or infracostal approaches ²³ . LP calyx is located in the lateral and anterior portion of kidney, meanwhile UP calyx is located in the medial posterior portion of the kidney. From this anatomical mapping, we can see that in patient placed in prone position the puncture access along with the kidney axis that performed from the posterior area is more effective and useful compared to anterior approach. Lower pole access approach has limited accessibility, particularly compared to the UP approach, to the visualize complete intrarenal collecting system in prone-position patients. A PCNL access through the lower pole calyx will form a more acute angle compared to upper pole calyx access due to the anatomical position of the kidney that has been stated above. Nevertheless, in some circumstances that PCNL in UP access is difficult to achieve, than a more lateral fashion of lower calyx access can also facilitate a wider angle of intrarenal access ²² .

The most common reason to perform LP approach is to minimize complications caused by the UP approach ² . However, although studies have shown that UP is associated with intrathoracic complications, we found that the rate of thoracic complications (hydrothorax and pneumothorax) did not differ between both groups (OR: 3.14; 95% CI: 0.63-15.62; P=0.16). Although previous studies demonstrated an increasing risks of intrathoracic and other complications associated with an upper pole access ^{24, 25} , in recent years these kind of complications have decreased exponentially in adult patients whom undergo PCNL for renal calculi ^{23, 24} . Furthermore, even if these thoracic complications did occur, the majority of patients that experienced these complications will recover either spontaneously or by simple intervention with minimal future comorbidity ²⁶ .

With these advantages, UP access is usually used as the preferred approach in selected patients with complex or staghorn renal calculi which need more than one intrarenal access. It has also been suggested that UP access is associated with increased bleeding. However, higher intraoperative bleeding in PCNL with UP access has been reported previously ¹¹ . But in this present meta-analysis, we did not find an increased requirement of blood transfusions in those whom undergoing PCNL with UP approaches (OR: 0.49; 95% CI: 0.14-1.76; P=0.27). Oner et al. ²⁷ performed 1750 PCNL procedures and found that upper calyx access is associated with a lower blood transfusion requirement and easier guidewire placement to the ureter, easier tract dilatation, and more comfortable manipulation. This suggests that UP access should be used if it facilitates stone clearance.

This meta-analysis found that there was no significant difference in terms of SFR and complications between staghorn calculi patients those underwent single UP-access PCNL and single NP-access PCNL. However, this study only included data with single PCNL access and there are only a few studies included in the present analysis. We suggest further multicenter randomized controlled trials are required to compare safety and efficacy of UP-access and NP-access PCNL for staghorn calculi patients.

The present analysis found that PCNL with single UP access has similar SFR and complication rates compared to single NP approach PCNL. Further randomized clinical trials are required to compare safety and efficacy of UP-access and NP-access PCNL.