Preoperative planning with noncontrast computed tomography in the prone and supine position for percutaneous nephrolithotomy: a practical overview

Optimizing Colon Identification by Window Setting Modulation on Noncontrast Computed Tomography Prior to Percutaneous Nephrolithotomy

Background: Preoperative identification of the bowel on imaging is essential in planning renal access during percutaneous nephrolithotomy (PCNL) and avoiding colonic injury. We aimed this study to assess which noncontrast computed tomography (NCCT) window setting provides the optimal colonic identification for PCNL preoperative planning. Methods: Ten urologic surgeons (four seniors, six residents) reviewed 22 images of NCCT scans in both abdomen and lung window settings in a randomized blinded order. Colonic area delineation in each image was performed using a dedicated, commercially available area calculator software. A comparison of the marked colonic area between the abdomen and lung window settings was performed. Results: Overall, the mean marked colonic area was greater in the lung window compared with the abdomen window (8.82 cm2 vs 7.4 cm2, respectively, p < 0.001). Switching the CT window from abdomen to lung increased the identified colonic area in 50 cases (50%). Intraclass correlation showed good agreement between the senior readers and among all readers (0.92 and 0.87, respectively). Similar measurements of the colonic area in both abdomen and lung windows were observed in 26/44 (60%) of the seniors cases and in 7/66 (10%) of the resident cases (p = 0.002). Conclusion: Lung window solely or in combination with abdomen window appears to provide the most accurate colonic identification for preoperative planning of PCNL access and potentially reduce the risk of colonic injury. This pattern is more evident among young urologists, and we propose to introduce it as a standard sequence in PCNL preplanning.

A mathematical method to estimate angle and distance for percutaneous renal puncture based on computed tomography data: Description and validation

Introduction

Gaining access to the kidney is crucial step in percutaneous nephrolithotomy (PCNL); it has a steep learning curve.

Objective

Describe the mathematical method to predict renal puncture angle and distance based on preoperative computed tomography (CT) measurements. Then evaluating how it correlates with measured values.

Patients and Methods

The study was prospectively designed. After ethical committee approval, the study uses data from preoperative CT to construct a triangle so we can estimate puncture depth and angle. A triangle of three points, the first is point of entry to the pelvicalyceal system (PCS), the second is point on the skin perpendicular to it, and the third where the needle punctures the skin. The needle travel is estimated using the Pythagorean theorem and puncture angle using the inverse sine function. We evaluated 40 punctures in 36 PCNL procedures. After PCS puncture using fluoroscopy-guided triangulation, we measured the needle travel distance and angle to the horizontal plane. Then compared the results with mathematically estimated values.

Results

We targeted posterior lower calyx in 21 (70%) case. The correlation between measured and estimated needle travel distance with Rho coefficient of 0.76 with P < 0.001. The mean difference between the estimated and the measured needle travel was - 0.37 ± 1.2 cm (-2.6-1.6). Measured and estimated angle correlate with Rho coefficient of 0.77 and P < 0.001. The mean difference between the estimated and the measured angle was 2° ± 8° (-21°-16°).

Conclusion

Mathematical estimation of needle depth and angle for gaining access to the kidney correlates well with measured values.

Renal Location Within the Retroperitoneum in Various Body Positions Using Magnetic Resonance Imaging: Implications for Percutaneous Nephrostolithotomy

OBJECTIVES

To assess the difference in cranio-caudal renal position in both the supine and prone position, as well as the effect of arm position on renal location, using magnetic resonance imaging in subjects with BMI <30.

METHODS

In a prospective IRB approved trial, healthy subjects underwent magnetic resonance imaging in the supine, prone position with arms at the side, and prone position with arms up using vertically placed towel bolsters. Images were obtained with end expiration breath holds. Distances between the kidney and other anatomical landmarks, including the diaphragm (KDD), top of the L1 vertebra (KVD) and lower edge of the 12^th rib (KRD), were recorded. Nephrostomy tract length (NTL) and other measures for visceral injury were also assessed. Wilcoxon signed rank test was used for analysis (p <0.05).

RESULTS

Ten subjects (5 male, 5 female) with median age of 29 years and BMI of 24 kg/m² were imaged. Right KDD was not significantly different between positions, but KRD and KVD noted significant cephalad movement when prone, as compared to supine. Left KDD noted caudal movement with prone positioning with no difference in KRD or KVD. Arm position did not affect any measurements. Right lower NTL was shorter when prone.

CONCLUSIONS

In subjects with BMI<30, prone positioning led to significant cephalad right renal movement, but not left renal movement. Arm position had no effect on anticipated renal position. Pre-operative end expiration supine CT may reliably predict left kidney location and be used to improve pre-operative counseling and/or surgical planning.

Retrorenal colon in pediatric patients with urolithiasis: Is the supine position for PCNL advantageous?

INTRODUCTION

Percutaneous nephrolithotomy (PCNL) is one of the main approaches for the treatment of large and complex stones in pediatric patients. The patient position for PCNL has been classically divided into prone or supine and the prone position is more commonly used. One of the most feared complications of this surgical technique is colon injury and the objective of this work is to evaluate the incidence of retrorenal colon (RRC) both supine and prone position, in pediatric patients, through radiological images.

MATERIALS AND METHOD

A retrosepctive review was performed of all abdominal CT scans performed in one center, in patients under 18 years since 2017 to 2019. The ideal path for percutaneous puncture was traced in the upper, middle, and lower calyces of both kidneys in the prone and supine positions and contact with the kidney and adjacent organs was evaluated, with a uro-radiologist. Chi-square test and Student's t test were applied.

RESULTS

50 CT-scans were performed on 44 children. Patients had a mean age of 12.6 years and 71.4% were male. Twenty-five scans were performed in the prone and 25 in the supine position. The incidence of RRC for the left kidney (LK) was significantly higher in the lower calyx in prone position than in the supine position, 28% vs 4% (p = 0.049), and the right kidney (RK) presented RRC only in the prone position. The liver was the most frequent retrorenal organ (97.7%) for the RK, with a non-significant difference by position, while for the LK the spleen was the most frequent (61.1%).

DISCUSSION

Colon injury is one of the most morbid complication in PCNL and one of the reasons to perform a CT scan before surgery, on which its incidence appears to be <1% in adults. The present study revealed RRC to be present in three (12%) patients in the supine position and seven (28%) patients in the prone position (p=0.15). These results were slightly higher from those reported in adults (supine: 1.7%-10%; prone: 6.8%-20%), but there are no reports in the literature on this issue to allow appropriate comparison. This is the first study to attempt to assess the incidence of RRC in children according to position.

CONCLUSION

The incidence of RRC for an ideal puncture was significantly higher in the lower calyx of the left kidney in the prone position than in the supine position, and in the right kidney, the RRC only occurred in the prone position.

International Alliance of Urolithiasis (IAU) Guideline on percutaneous nephrolithotomy

The International Alliance of Urolithiasis (IAU) would like to release the latest guideline on percutaneous nephrolithotomy (PCNL) and to provide a clinical framework for surgeons performing PCNLs. These recommendations were collected and appraised from a systematic review and assessment of the literature covering all aspects of PCNLs from the PubMed database between January 1, 1976, and July 31, 2021. Each generated recommendation was graded using a modified GRADE methodology. The quality of the evidence was graded using a classification system modified from the Oxford Center for Evidence-Based Medicine Levels of Evidence. Forty-seven recommendations were summarized and graded, which covered the following issues, indications and contraindications, stone complexity evaluation, preoperative imaging, antibiotic strategy, management of antithrombotic therapy, anesthesia, position, puncture, tracts, dilation, lithotripsy, intraoperative evaluation of residual stones, exit strategy, postoperative imaging and stone-free status evaluation, complications. The present guideline on PCNL was the first in the IAU series of urolithiasis management guidelines. The recommendations, tips and tricks across the PCNL procedures would provide adequate guidance for urologists performing PCNLs to ensure safety and efficiency in PCNLs.

Application of a novel computer-assisted surgery system in percutaneous nephrolithotomy: A controlled study

BACKGROUND

Most complex renal stones are managed primarily with percutaneous nephrolithotomy (PCNL). However, PCNL is still a great challenge for surgeons because of poor comprehension on complex adjacent structures. Novel techniques are required to assist in planning and navigation.

AIM

To apply and evaluate the Hisense computer-assisted surgery (CAS) system in PCNL.

METHODS

A total of 60 patients with complex renal stones were included. Thirty patients in the CAS group had three-dimensional (3D) virtual models constructed with the CAS system. The model assisted in planning and navigating in the CAS system. Thirty patients in the control group planned and navigated as standard PCNL, without the application of the CAS system. Success rate of one attempt, operation time, initial stone-free rate, decrease in hemoglobin, and complications were collected and analyzed.

RESULTS

There were no statistically significant differences in the baseline characteristics or planning characteristics. The success rate of one puncturing attempt (90% vs 67%, P = 0.028) and the initial stone-free rate (87% vs 63%, P = 0.037) were significantly higher in the CAS group. However, there were no statistically significant differences in the operation time (89.20 ± 29.60 min vs 92.33 ± 33.08 min, P = 0.859) or in the decrease in hemoglobin (11.07 ± 8.32 g/L vs 9.03 ± 11.72 g/L, P = 0.300) between the CAS group and the control group. No statistically significant differences in the incidence of complications (Clavien-Dindo grade ≥ 2) were found.

CONCLUSION

Compared with standard PCNL, CAS-assisted PCNL had advantages in terms of the puncturing success rate and stone-free rate. The Hisense CAS System was recommended to assist in preoperative planning and intraoperative navigation for an intuitive, precise and convenient PCNL.

THE FUNCTIONAL STATE OF THE RENAL PARENCHYMA AFTER VARIOUS VIDEO ENDOSURGICAL METHODS OF TREATMENT OF PATIENTS WITH LARGE AND COMPLEX KIDNEY STONES

The work is based on the analysis of literature data devoted to the problem of preserving the functional state of the kidneys with various video endoscopic methods of surgical treatment of large and complex kidney stones. The purpose of the review is to highlight the likelihood of deterioration in the functional state of the kidneys in the postoperative period. A detailed analysis of postoperative outcomes in various minimally invasive methods of treatment of patients with large and complex kidney stones was carried out, with an overview of the possibility of using dynamic nephroscintigraphy as a method of objectively assessing the functional state of the kidneys.

Incidence of posterolateral and retrorenal colon in supine and prone position in percutaneous nephrolithotomy

Colon injury is a distressing complication during percutaneous nephrolithotomy (PCNL). Posterolateral colon (PLC) and retrorenal colon (RRC) are known to be the risk factors of colonic injury during PCNL. We evaluated the incidence of PLC and RRC in both supine and prone position of patients who underwent PCNL in our institution, and determined the risk factors of PLC and RRC through a review of computed tomography (CT) scan. To define PLC and RRC, we divided kidney into anterior, anterolateral, posterolateral and retrorenal zone by drawing three parallel lines in the CT scan. Among a total of 102 patients, PLC and RRC were identified in 16 (15.7%) cases in supine, and 25 (24.5%) cases in the prone position. PLC and RRC were most frequently present in the upper and lower pole of the left kidney in prone position compared to supine (p value less than 0.001). Risk factors of PLC and RRC in the prone position were old age (over 68), lower body mass index (BMI), and thinner perirenal fat layer. Therefore, an initial percutaneous puncture in PCNL needs to be carefully accessed to those patients with such high risks of colon injury.

Effects of horizontal versus vertical bolster alignment on anatomical orientation of kidney as applied to prone percutaneous nephrolithotomy

PURPOSE

To evaluate the anatomical changes in kidney orientation in prone position with use of horizontal or vertical bolster alignment.

METHODS

Patients having renal stone(s) on ultrasonogram or X-ray underwent split bolus computed-tomo-urography (CTU) in prone position with horizontal and vertical bolster positions. CTUs were read by a single radiologist to quantify the cranio-caudal, antero-posterior, side to side and rotational movements of kidneys as relevant to prone percutaneous nephrolithotomy.

RESULTS

19 adult patients with 38 renal units and mean basal metabolic index of 25.6 kg/m² underwent CTU. Greater inferior displacement of both kidneys was seen with horizontal bolsters as compared to vertical bolsters. The right upper calyceal-diaphragm distance was 2.1 ± 1.5 cm and the lower calyceal-diaphragm distance was 2.0 ± 1.6 cm greater with the horizontal bolsters (p < 0.01). Similarly, the displacement on the left side was 1.5 ± 0.8 cm and 1.4 ± 0.8 cm, respectively (p < 0.01). Horizontal bolsters also result in significantly longer calyceal-skin distance at both poles of both kidneys [right upper: 0.4 ± 0.5 cm (p < 0.01), right lower: 0.8 ± 0.7 cm (p < 0.01), left upper: 0.4 ± 0.6 cm (p = 0.02), left lower: 0.8 ± 1.1 cm (p < 0.01)] and wider erector spinae-mid posterior calyceal-colon angle (124.8 v/s 110.0 on the right and 96.2 v/s 85.7 on the left) (p < 0.01).

CONCLUSION

Horizontal bolsters provide significantly more caudal displacement of the kidneys; the right kidney being displaced more as compared to the left. However, there is also an increase in the skin-calyceal distance with horizontal as compared to the vertical bolsters. These assessments may help the surgeons decide optimal bolster position individualized to the patient.

New computed tomographic predictors of complicated perioperative course of 17.5F mini-percutaneous nephrolithotomy (mini-PNL)

PURPOSE

Radiological parameters predicting a postoperative stone-free status (SFS) or a complicated perioperative course of mini-PNL, are scarce. Our aim was to identify such factors for prone 17.5F mini-PNL.

METHODS

A monocentric cohort of 103 cases was retrospectively analysed for factors predicting SFS and relevant complications, i.e. Clavien-Dindo (CD) ≥ 2. Parameters measured on preoperative supine CT included maximal stone diameter, skin-to-stone distance (SSD), ideal tract length (ITL), access angle, minimal T12-Lower Kidney Pole distance (T12LP) and minimal Iliac Crest-Lower Kidney Pole distance (ICLP). Infundibulopelvic angle (IPA) was measured on intraoperative pyelography.

RESULTS

The median maximal stone diameter was lower in cases with postoperative SFS [16 mm (Min. 10; Max. 35) vs. 20 mm (Min. 6; Max. 85), p = 0.0052]. CD ≥ 2 was more frequent in cases with a bigger stone burden [19 mm (Min. 13; Max. 85) vs. 16 mm (Min. 6; Max. 49), p = 0.0056] and with the ribs in the access angle [7/23 (30.43%) vs. 8/76 (10.53%); p = 0.0454]. T12LP significantly differed in cases with and without CD ≥ 2 [80.48 mm (± 21.31) vs. 90.43 mm (± 19.42), p = 0.0397]; however, it had no influence on SFS (p > 0.05). SSD, ITL, IPA and ICLP were significant regarding neither SFS nor CD ≥ 2 prevalence (p > 0.05). Using multivariate logistic regression, T12LP was confirmed as an independent predictor on CD ≥ 2 prevalence.

CONCLUSIONS

Preoperative computed tomographic factors indicating elevated kidney position influence perioperative course of mini-PNL. T12LP and the presence of ribs in the access angle are, apart from stone diameter, the most useful indicators for cases at risk of CD ≥ 2.

Percutaneous nephrolithotomy for staghorn calculi: Troubleshooting and managing complications

Staghorn calculi comprise a unique subset of complex kidney stone disease. Percutaneous nephrolithotomy (PCNL) is the gold standard treatment for staghorn stones. Despite continuous refinements to the technique and instrumentation of PCNL, these stones remain a troublesome challenge for endourologists and are associated with a higher rate of perioperative complications than that for non-staghorn stones. Common and notable intraoperative complications include bleeding, renal collecting system injury, injury of visceral organs, pulmonary complications, thromboembolic complications, extrarenal stone migration, and misplacement of the nephrostomy tube. Postoperative complications include infection and urosepsis, bleeding, persistent nephrocutaneous urine leakage, infundibular stenosis, and death. In this review, we report recommendations regarding troubleshooting measures that can be used to identify and characterize these complications. Additionally, we include information regarding management strategies for complications associated with PCNL for staghorn calculi.

Comparative study of percutaneous nephrolithotomy performed in the traditional prone position and in three different supine positions

Purpose:

To compare the outcomes of percutaneous nephrolithotomy (PCNL) performed in the prone position (PRON) and in three variations of the supine position.

Materials and Methods:

We performed a retrospective analysis of patients that underwent PCNL at our institution from June 2011 to October 2016 in PRON and in three variations of the supine position: complete supine (COMPSUP), original Valdivia (VALD), and Galdakao - modified Valdivia (GALD). All patients had a complete pre - operative evaluation, including computed tomography (CT). Success was defined as the absence of residual fragments larger than 4 mm on the first post - operative day CT.

Results:

We analyzed 393 PCNLs: 100 in COMPSUP, 94 in VALD, 100 in GALD, and 99 in PRON. The overall success rate was 50.9% and was similar among groups (p = 0.428). There were no differences between groups in the number of punctures, stone - free rate, frequency of blood transfusions, drop in hemoglobin level, length of hospital stay, and severe complications (Clavien ≥ 3). COMPSUP had a significantly lower operative time than the other positions. COMPSUP had lower fluoroscopy time than VALD.

Conclusion:

Patient positioning in PCNL does not seem to impact the rates of success or severe complications. However, COMPSUP is associated with a shorter surgical time than the other positions.

Impact of patient position on the outcomes of percutaneous neprolithotomy for complex kidney stones

Purpose:

To evaluate the impact of the patient position on the outcomes of PCNL among patients with complex renal stones.

Material and Methods:

From July 2011 to July 2014, we collected prospective data of consecutive patients who underwent PCNL. We included all patients with complex stones (Guy's Stone Score 3 or 4 (GSS) based on a CT scan) and divided them based on the position used during PCNL (prone or supine). The variables analyzed were gender, age, body mass index, ASA score, stone diameter, GSS, number of punctures, calyx puncture site, intercostal access and patient positioning. Complications were graded according to the modified-Clavien Classification. Success was considered if fragments ≤ 4mm were observed on the first postoperative day CT scan.

Results:

We analyzed 240 (46.4%) of 517 PCNL performed during the study period that were classified as GGS 3-4. Regarding patient positions, 21.2% were prone and 79.8% were supine. Both groups were comparable, although intercostal access was more common in prone cases (25.5% vs 10.5%; p=0.01). The success rates, complications, blood transfusions and surgical times were similar for both groups; however, there were significantly more visceral injuries (10.3% vs 2.6%; p=0.046) and sepsis (7.8% vs 2.1%; p=0.042) in prone cases.

Conclusion:

Supine or prone position were equally suitable for PCNL with complex stones and did not impact the success rates. However, supine position was associated with fewer sepsis cases and visceral injuries.

Prone Percutaneous Nephrolithotomy: Does Bolster Orientation Matter?

OBJECTIVE

To assess whether horizontal vs vertical bolster orientation affects kidney position during prone percutaneous nephrolithotomy as this could impact the need for supracostal access and therefore the likelihood of pleural injury.

MATERIALS AND METHODS

In a prospective trial, 10 subjects with 20 renal units underwent magnetic resonance imaging in prone position with standard cylindrical bolsters oriented vertically and then horizontally. Vertical bolsters were placed along the lateral aspect of the chest. Horizontal bolsters were placed at the xiphoid and symphysis pubis. The position of the kidney relative to the pleura was assessed by measuring distances from the kidney upper pole to diaphragm, to the top of the first lumbar vertebra, and inferior-most rib. Nephrostomy tract length and tract proximity to adjacent organs were also measured.

RESULTS

Right and left kidney-to-diaphragm distance significantly increased with horizontal vs vertical bolsters by 3.44 cm and 1.86 cm, respectively (P = .02, P = .01). Right kidney-to-rib distance significantly increased by 2.4 cm (P = .025); left kidney-to-rib distance increased by 0.5 cm (P = .123). Right kidney-to-vertebral distance significantly increased by 2.16 cm (P = .007); left kidney-to-vertebral distance increased by 0.9 cm (P = .059). There was no significant difference in maximum access angle, overall tract length, or colon position between horizontal and vertical bolsters.

CONCLUSION

Orienting bolsters horizontally results in caudal kidney displacement without affecting access angle, overall tract length, or colon position. In comparison with vertical orientation, this may improve safety of percutaneous nephrolithotomy by decreasing the need for supracostal access and increasing the safety of supracostal access when required.

Comparison of supine and prone positions for percutaneous nephrolithotomy in treatment of staghorn stones

INTRODUCTION

Percutaneous nephrolithotomy (PNL) is the primary treatment modality for management of staghorn stones. PNL in supine position has important advantages over prone positon. However, studies comparing prone and supine positions for PNL in staghorn stone patients have conflicting results, and the aim of the current study was to compare prone and supine positions for PNL in staghorn stone cases.

PATIENTS AND METHODS

Data of patients underwent PNL for staghorn stones in supine or prone position by a single urologist were collected prospectively. The supine and prone position groups were compared for stone free rate (SFR) and complication rates. All patients were evaluated with NCCT for evaluation of SFR. Chi-square test was used to compare categorical variables and Student t test was applied for continuous variables of the treatment groups.

RESULTS

The groups were similar for demographic and stone-related characteristics. Multi-caliceal and intercostal access was more common in prone position. Operation duration was significantly shorter and hemoglobin drop was significantly less in supine group. SFR was 64.1 and 60.4% in the supine and prone groups, respectively (p = 0.72). Complication rates were similar in the two groups but Clavien III complications were observed in two patients in the prone group.

CONCLUSIONS

PNL in supine position is an effective treatment for management of staghorn stones. The need for multi-caliceal and intercostal puncture is less when combined with retrograde intrarenal surgery. PNL in supine position should be considered as primary treatment option in staghorn stone cases.

Positioning for percutaneous nephrolithotomy

PURPOSE OF THE REVIEW

To highlight the progressive evolution of the issue of patient positioning for percutaneous nephrolithotomy (PNL), explain the history of the prone and supine positions, report respective advantages and drawbacks, critically interpret the past and current literature supporting such arguments, identify the best candidates for each position, and reflect on the future evolution of the two approaches.

RECENT FINDINGS

Positioning for PNL has become a matter of debate during the last decade. The traditional prone PNL position - most widely performed with good success and few complications, and exhibiting essentially no limits except for the treatment of pelvic kidneys - is nowadays flanked mainly by the supine and supine-modified positions, equally effective and probably safer from an anesthesiological point of view. Of course, both approaches have a number of advantages and drawbacks, accurately reported and critically sieved.

SUMMARY

The current challenge for endourologists is to be able to perform PNL in both prone and supine positions to perfectly tailor the procedure on any patient with any stone burden, including increasingly challenging cases and medically high-risk patients, according to the patient's best interest. Intensive training and experience is especially needed for supine PNL, still less popular and underperformed worldwide.

VIDEO ABSTRACT

http://links.lww.com/COU/A8.