Kidney Targeting and Puncturing During Percutaneous Nephrolithotomy: Recent Advances and Future Perspectives

Feasibility of stereotactic optical navigation for needle positioning in percutaneous nephrolithotomy

BACKGROUND

This study assessed the feasibility of acquiring single-attempt access to the pelvicalyceal system during percutaneous nephrolithotomy (PCNL) using stereotactic optical navigation combined with cone-beam CT (CBCT) imaging.

METHODS

Patients with a PCNL indication were prospectively included in this IRB approved study. After sterile preparation, fiducial markers were attached to patients' skin. An initial intraprocedural CBCT scan was acquired, on which the urologist planned the needle trajectory using the navigation software. After verifying that no critical structures were crossed, the needle guide was aligned with the plan. A needle was manually inserted through the needle guide to the indicated depth and a second CBCT scan was performed for needle position confirmation. Both, scanning and needle insertion, were performed under apnea. The study evaluated technical success, accuracy, procedure time, complication rate, and radiation dose.

RESULTS

Between June 2022 and April 2023, seven patients were included. In all patients, the navigation system allowed safe puncture. However, the technical success rate was only 29%. In 42% of the cases, pelvicalyceal access was achieved by a small manual adjustment. In the remaining 29%, the needle was retracted and positioned per clinical standard. The average deviation between the needle and target was 5.9 ± 2.3 mm. The average total procedure time was 211 ± 44 min. The average radiation exposure was 6.4 mSv, with CBCT scanning contributing to 82% of this exposure.

CONCLUSIONS

The optical navigation system facilitated safe needle insertion but did not consistently ensure accurate one-attempt needle positioning for PCNL. Real-time visualization and trajectory correction may improve the technical success rate.

Application of image overlapping in percutaneous nephrolithotomy

OBJECTIVE

To investigate the application of ultrasound and CT image overlap in percutaneous nephrolithotomy (PCNL).

METHODS

A total of 140 patients with complicated kidney stones requiring PCNL were prospectively enrolled, from January 2020 to December 2022. These patients were randomly divided into 2 groups, with 70 patients each in the research group and the control group. All participants underwent dual-source, non-contrast CT scan of both kidneys and pelvis before surgery. Preoperative three-dimensional CT reconstruction and simulated puncture were performed in patients from the research group. The best puncture path was determined through ultrasound and CT image overlap. Puncture guided by regular CT and ultrasound was conducted in patients from the control group. Differences in the surgical outcomes between the two groups were compared.

RESULTS

Compared to the control group, the research group had higher stone clearance rate in stage I PCNL, success rate of one-time puncture, less percutaneous channels, less reduction of hemoglobin and shorter procedure time. Complications in stage I PCNL were comparable in the two groups, and there was no significant change in the final stone clearance rates between the two groups.

CONCLUSION

An optimal puncture channel can be chosen using ultrasound and CT image overlap. PCNL can be achieved with precise puncturing, thus achieving coincidence between imaging and anatomy and reducing the amount of blood loss during stage I of PCNL. It also shortens the procedure time and improves stone clearance rate of PCNL.

Radiation protection measures during endourological therapies

Objective

The objective of this narrative review was to search the existing literature for studies reporting measures to minimize radiation use during endoscopic management of stone disease and present ways of reducing the exposure of both patients and operating room staff.

Methods

A literature review in PubMed was performed to identify studies describing protocols or measures to reduce radiation received during endourological procedures from January 1970 to August 2022. Eligible studies were those that reported outcomes for ureteroscopy or percutaneous nephrolithotripsy regarding measures to minimize radiation doses used intraoperatively, performed either in real-life theatres or using phantoms. Both comparative and non-comparative studies were deemed eligible.

Results

Protection can be achieved initially at the level of diagnosis and follow-up of patients, which should be done following an algorithm and choice of more conservative imaging methods. Certain protocols, which follow principles for minimized fluoroscopy use should be implemented and urologists as well as operating room staff should be continuously trained regarding radiation damage and protection measures. Wearing protective lead equipment remains a cornerstone for personnel protection, while configuration of the operating room and adjusting X-ray machine settings can also significantly reduce radiation energy.

Conclusion

There are specific measures, which can be implemented to reduce radiation exposure. These include avoiding excessive use of computed tomography scans and X-rays during diagnosis and follow-up of urolithiasis patients. Intraoperative protocols with minimal fluoroscopy use can be employed. Staff training regarding dangers of radiation plays also a major role. Use and maintenance of protective equipment and setting up the operating room properly also serve towards this goal. Machine settings can be customized appropriately and finally continuously monitoring of exposure with dosimeters can be adopted.

Prevalence of the Retro-Renal Colon: A Systematic Review and Meta-Analysis with Implications for Percutaneous Nephrolithotomy

BACKGROUND

This systematic review and meta-analysis aims to determine the prevalence of the retrorenal colon (RRC) and its implications in percutaneous nephrolithotomy with the overall objective of promoting the prevention of associated iatrogenic complications.

METHODS

A systematic search of literature was conducted on the electronic databases PubMed, ScienceDirect, and Hinari to identify studies eligible for inclusion. Search results were screened by title and abstract, and those potentially relevant were evaluated by full text. Studies were deemed eligible for inclusion if they reported clear extractable data regarding the prevalence of the retro-renal colon. A meta-analysis was completed using MetaX1 to calculate the pooled prevalence of the retro-renal colon. Sub-group analysis was performed based on geographical regions from which the studies originated, imaging modality, and patient position.

RESULTS

174 records were screened and a total of 10 records included in the analysis with retrospective cohort studies being the most common study design. A male predominance was seen in most sample sizes that had reported data on gender demographics ranging from 41.5-62%. The most common imaging modality utilized was computerized tomography (CT) scan followed by ultrasound. The range of the unweighted prevalence of retro-renal colon across all studies that had absolute numbers reported was from 3.5-25%. One of the studies reported a colonic perforation rate of 0.3% in patients without CT images.

CONCLUSION

The retro-renal colon is a relatively common finding with observed preponderance to females and left lateralization. The presence of RRC increases the likelihood of colon perforations while gaining percutaneous access to the kidney. Pre-procedural imaging can help detect its presence and choose an appropriate route of entry. USG and CT have both been found useful as a modality to pick up RRC.

Percutaneous Kidney Puncture with Three-dimensional Mixed-reality Hologram Guidance: From Preoperative Planning to Intraoperative Navigation

BACKGROUND

Despite technical and technological innovations, percutaneous puncture still represents the most challenging step when performing percutaneous nephrolithotomy. This maneuver is characterized by the steepest learning curve and a risk of injuring surrounding organs and kidney damage.

OBJECTIVE

To evaluate the feasibility of three-dimensional mixed reality (3D MR) holograms in establishing the access point and guiding the needle during percutaneous kidney puncture.

DESIGN, SETTING, AND PARTICIPANTS

This prospective study included ten patients who underwent 3D MR endoscopic combined intrarenal surgery (ECIRS) for kidney stones from July 2019 to January 2020. A retrospective series of patients who underwent a standard procedure were selected for matched pair analysis.

SURGICAL PROCEDURE

For patients who underwent 3D MR ECIRS, holograms were overlapped on the real anatomy to guide the surgeon during percutaneous puncture. In the standard group, the procedures were only guided by ultrasound and fluoroscopy.

MEASUREMENTS

Differences in preoperative and postoperative patient characteristics between the groups were tested using a χ² test and a Kruskal-Wallis test for categorical and continuous variables, respectively. Results are reported as the median and interquartile range for continuous variables and as the frequency and percentage for categorical variables.

RESULTS AND LIMITATIONS

Ten patients underwent 3D MR ECIRS. In all cases, the inferior calyx was punctured correctly, as planned using the overlapping hologram. The median puncture and radiation exposure times were 27 min and 120 s, respectively. No intraoperative or major postoperative complications occurred. Matched pair analysis with the standard ECIRS group revealed a significantly shorter radiation exposure time for the 3D MR group (p < 0.001) even though the puncture time was longer in comparison to the standard group (p < 0.001). Finally, use of 3D MR led to a higher success rate for renal puncture at the first attempt (100% vs 50%; p = 0.032). The main limitations of the study are the small sample size and manual overlapping of the rigid hologram models.

CONCLUSIONS

Our experience demonstrates that 3D MR guidance for renal puncture is feasible and safe. The procedure proved to be effective, with the inferior calyx correctly punctured in all cases, and was associated with a low intraoperative radiation exposure time because of the MR guidance.

PATIENT SUMMARY

Three-dimensional virtual models visualized as holograms and intraoperatively overlapped on the patient's real anatomy seem to be a valid new tool for guiding puncture of the kidney through the skin for minimally invasive treatment.

Case selection and implementation of tubeless percutaneous nephrolithotomy

Background

The tubeless percutaneous nephrolithotomy (PCNL) was proposed to eliminate the side effects of the nephrostomy tube in recent years, such as pain, channel infection, postoperative bleeding, and longer hospital stay. But there is neither clinical guidelines nor consensus about tubeless PCNL in clinical practice. The study is aimed to how to implement the tubeless PCNL step by step, including case selection preoperatively, improving the technique of the surgeon, making the correct decisions at the end of the procedure, which had not been previously examined.

Methods

From January 2017 to March 2018, 364 consecutive patients requiring PCNL were comprehensively analyzed preoperatively and patients were selected for scheduled tubeless PCNL based on four aspects. The selected patients were divided into two groups according to whether the nephrostomy tube was finally placed. The mean operative time, intraoperative blood loss, stone clearance rate, visual pain score, postoperative hospitalization days and perioperative complications were all evaluated.

Results

Based on the preoperative evaluation, 42 patients were selected for tubeless PCNL, among which there were finally 37 cases of completed tubeless PCNL. Compared with patients undergoing conventional PCNL, there were not statistical differences in the mean operative time (P=0.207) or intraoperative blood loss (P=0.450) in the tubeless group. Stone clearance rate was 100% in both groups. The visual pain scores in the tubeless PCNL group were lower on operation day (P=0.029), first postoperative day (P<0.001) and the day of discharge (P=0.025). The postoperative hospitalization for the tubeless PCNL group was shorter than that of the control group (P<0.001). No significant difference in grade 1 complications was seen (P=0.424), and no grade 2 or higher complications were observed in either group.

Conclusions

Postoperative pain was significantly relieved and postoperative hospitalization was significantly shortened in the tubeless PCNL group. Tubeless PCNL is safe if patients are carefully selected using four criteria before operation, attention is paid to four key points and five confirmations are made during operation.

How does puncture modality affect the risk of intraoperative bleeding during percutaneous nephrolithotomy? A prospective randomized trial

INTRODUCTION AND OBJECTIVES

To evaluate the possible effects of two different renal puncture techniques (ultrasound-assisted [US-assisted], fluoroscopic-guided [FG]) on the intraoperative hemorrhage risk during percutaneous nephrolithotomy (PCNL).

MATERIAL AND METHODS

A total of 130 patients with Guy stone scores of 1-2 were prospectively allocated to US-assisted and FG puncture groups by simple randomization. Patients with intraoperative pelvicalyceal rupture and the ones requiring multiple accesses were excluded from the study. Apart from the puncture steps, all other steps of the PCNL procedure were performed with similar techniques by a single surgeon. Patient characteristics, operative data, and postoperative outcomes were compared.

RESULTS

A total of 10 patients were excluded from the study due to intraoperative complications after puncture. Patient demographics and stone characteristics were similar between the two groups (p > 0.05). Mean hemoglobin drop was meaningfully greater in the FG group (1.7 g/dL) when compared with US-assisted group (1.3 g/dL) (p < 0.01). The mean duration of radiation exposure was significantly higher for the FG (p < 0.001). Total operative time, number of attempts for a successful puncture, length of hospital stay, and stone free rates were similar between the groups (p > 0.05). In addition, the remaining complications classified according to the modified Clavien-Dindo grading system were similar between groups (p > 0.05).

CONCLUSION

US-assisted puncture provides significantly decreased level of hemoglobin drop and radiation exposure time when compared with FG.

Electric impedance spectroscopy feature extraction for tissue classification with electrode embedded surgical needles through a modified forward stepwise method

There has been a growing interest in developing electric impedance sensing surgical tools for tissue identification during surgery. A key facet of this development is identifying distinct features that can be used to identify tissues from one another. This paper explores several feature extraction techniques and classification methods applied to electric impedance data. Furthermore, a modified forward stepwise method is proposed. The method introduces a scoring metric to help select features to add to the model, that is based off of the coefficient of variation and overlapping index from the feature's probability density functions for each of the classes. The proposed and existing methods were applied to spectral data measured at 23 frequencies, from 132 samples across 6 different tissues including ex-vivo bovine kidney, liver and muscle, poultry liver, as well as freshly excised canine testicle and ovary samples. These methods were able to successfully find impedance spectra features for the investigated biological tissues. The best predictive accuracy was with Boruta feature extraction and a Random Forest classifier but without significantly reducing the number of features in the classifier model. The proposed method was able to reduce the number of features in the model to an average of 5.8 features for all tested classifiers. These methods may have use in finding features to discriminate other tissue types, possibly to aid in targeting lesions in minimally invasive cancer treatment surgeries.

How does puncture modality affect the risk of intraoperative bleeding during percutaneous nephrolithotomy? A prospective randomized trial

INTRODUCTION AND OBJECTIVES

To evaluate the possible effects of two different renal puncture techniques (ultrasound-assisted [US-assisted], fluoroscopic-guided [FG]) on the intraoperative hemorrhage risk during percutaneous nephrolithotomy (PCNL).

MATERIAL AND METHODS

A total of 130 patients with Guy stone scores of 1-2 were prospectively allocated to US-assisted and FG puncture groups by simple randomization. Patients with intraoperative pelvicalyceal rupture and the ones requiring multiple accesses were excluded from the study. Apart from the puncture steps, all other steps of the PCNL procedure were performed with similar techniques by a single surgeon. Patient characteristics, operative data, and postoperative outcomes were compared.

RESULTS

A total of 10 patients were excluded from the study due to intraoperative complications after puncture. Patient demographics and stone characteristics were similar between the two groups (P>.05). Mean hemoglobin drop was meaningfully greater in the FG group (1.7g/dL) when compared with US-assisted group (1.3g/dL) (P<.01). The mean duration of radiation exposure was significantly higher for the FG (P<.001). Total operative time, number of attempts for a successful puncture, length of hospital stay, and stone free rates were similar between the groups (P>.05). In addition, the remaining complications classified according to the modified Clavien-Dindo grading system were similar between groups (P>.05).

CONCLUSION

US-assisted puncture provides significantly decreased level of hemoglobin drop and radiation exposure time when compared with FG.

Technical Note: Assessment of electromagnetic tracking systems in a surgical environment using ultrasonography and ureteroscopy instruments for percutaneous renal access

PURPOSE

Electromagnetic tracking systems (EMTSs) have been proposed to assist the percutaneous renal access (PRA) during minimally invasive interventions to the renal system. However, the influence of other surgical instruments widely used during PRA (like ureteroscopy and ultrasound equipment) in the EMTS performance is not completely known. This work performs this assessment for two EMTSs [Aurora^® Planar Field Generator (PFG); Aurora^® Tabletop Field Generator (TTFG)].

METHODS

An assessment platform, composed by a scaffold with specific supports to attach the surgical instruments and a plate phantom with multiple levels to precisely translate or rotate the surgical instruments, was developed. The median accuracy and precision in terms of position and orientation were estimated for the PFG and TTFG in a surgical environment using this platform. Then, the influence of different surgical instruments (alone or together), namely analogic flexible ureterorenoscope (AUR), digital flexible ureterorenoscope (DUR), two-dimensional (2D) ultrasound (US) probe, and four-dimensional (4D) mechanical US probe, was assessed for both EMTSs by coupling the instruments to 5-DOF and 6-DOF sensors.

RESULTS

Overall, the median positional and orientation accuracies in the surgical environment were 0.85 mm and 0.42° for PFG, and 0.72 mm and 0.39° for TTFG, while precisions were 0.10 mm and 0.03° for PFG, and 0.20 mm and 0.12° for TTFG, respectively. No significant differences were found for accuracy between EMTSs. However, PFG showed a tendency for higher precision than TTFG. AUR, DUR, and 2D US probe did not influence the accuracy and precision of both EMTSs. In opposition, the 4D probe distorted the signal near the attached sensor, making readings unreliable.

CONCLUSIONS

Ureteroscopy- and ultrasonography-assisted PRA based on EMTS guidance are feasible with the tested AUR or DUR together with the 2D probe. More studies must be performed to evaluate the probes and ureterorenoscopes' influence before their use in PRA based on EMTS guidance.

A Fiber Bragg Grating Sensing Structure for the Design, Simulation and Stress Strain Monitoring of Human Puncture Surgery

In order to improve the precision and stability of puncture surgical operations to assist doctors in completing fine manipulation, a new of type puncturing needle sensor is proposed based on a fiber Bragg grating (FBG). Compared with the traditional puncture needle sensor, the new type of puncturing needle sensor is able to sense not only the axial force, but also the torque force during the puncture process. A spoke-type structure is designed near the needle tip. In order to eliminate the influence of temperature and realize temperature compensation, a reference fiber method using three FBGs is applied. FBG1 and the reference FBG2 are pasted on the upper and lower surfaces of the new-type elastic beam, and FBG3 is pasted into the groove on the surface of the new type of puncturing needle cylinder. The difference of Bragg wavelength between FBG1 and the reference FBG2 is calibrated with the torque force, while the difference between the Bragg wavelength of the FBG3 and the reference FBG2 is calibrated with the axial force. Through simulation and sensing tests, when the torque force calibration range is 10 mN·m, the torque average sensitivity is 22.8 pm/mN·m, and the determination coefficient R2 is 0.99992, with a hysteresis error YH and repetition error YR of 0.03%FS and 0.81%FS, respectively. When the axial force calibration rang is 5 N, the axial force average sensitivity is 0.089 nm/N, and the determination coefficient R2 is 0.9997, with hysteresis error YH and repetition error YR of 0.014%FS and 0.11%FS, respectively. The axial force resolution and torque resolution of the new type of puncturing needle sensor are 0.03 N and 0.8 mN·m, respectively. The experimental data and simulation analysis show that the proposed new type of puncturing needle sensor has good practicability and versatility.

The Anatomic Structure of a Fused Renal Pyramid and Its Clinical Significance in the Establishment of Percutaneous Renal Access

OBJECTIVE

To explore the clinical significance of the fused renal pyramid (FRP) in establishing percutaneous renal access, and the anatomic basis for avoiding vascular injury caused by puncturing through this renal pyramid with the aim of achieving accurate puncture in percutaneous nephrolithotomy.

MATERIALS AND METHODS

Sixty-two cadaveric kidneys and 105 porcine kidneys were selected for the assessment of regional anatomy, to explore the anatomic structure of the FRP and determine its frequency. Then, we compared the effects of 4 different puncture paths on the occurrence of renal vascular injury when respectively punctured through the normal renal pyramid (group A), the centerline of one side pyramid of the FRP (group B), the center of the entire FRP (group C) and the renal column (group D).

RESULTS

The incidence of FRP in human kidneys is not low. The artery in the kidney can be divided into 6 grades. The grade IV branch-interlobar artery courses through the FRP. There was significant difference in the degree of arterial injury between the group A and C (P = .003), while no significant difference between the group A and B (P = .151). There was significant difference in the proportion of interlolar artery injury between group A and C (P <.001), while no significant difference between group A and B (P = .239).

CONCLUSION

It is necessary to carefully identify and bypass the FRP when establishing a percutaneous renal access. If unavoidable, the puncture path should be on the centerline of one side pyramid of the FRP.

Present indications and techniques of percutaneous nephrolithotomy: What the future holds?

The purpose of the review was to present the latest updates on percutaneous nephrolithotomy (PCNL) procedure in terms of indications and evolving techniques, and to identify the advantages and disadvantages of each modality. The data for this review were collected after a thorough PubMed search in core clinical journals in English language. The key words included “PCNL” and “PNL” in combination with “indications”, “techniques”, “review” and “miniaturized PCNL”. Publications relevant to the subject were retrieved and critically reviewed. Current European and American Urology Association Nephrolithiasis Guidelines were included as well. The indications for standard PCNL have been changed through the past decade. Despite evolution of the procedure, innovations and the development of new technical approaches, the indications for miniaturized PCNL have not been standardized yet. There is a need for well-constructed randomized trials to explore the indications, complications and results for each evolving approach. A continuous reduction of tract size is not the only revolution of the last years. There is constant ongoing interest in developing new efficient miniature instruments, intracorporeal lithotripters and sophisticated tract creation methods. We can summarize that, PCNL represents a valuable well-known tool in the field of endourology. We should be open minded to future changes in surgical approaches and technological improvements.

Kidney segmentation in ultrasound, magnetic resonance and computed tomography images: A systematic review

BACKGROUND AND OBJECTIVE

Segmentation is an essential step in computer-aided diagnosis and treatment planning of kidney diseases. In recent years, several researchers proposed multiple techniques to segment the kidney in medical images from distinct imaging acquisition systems, namely ultrasound, magnetic resonance, and computed tomography. This article aims to present a systematic review of the different methodologies developed for kidney segmentation.

METHODS

With this work, it is intended to analyze and categorize the different kidney segmentation algorithms, establishing a comparison between them and discussing the most appropriate methods for each modality. For that, articles published between 2010 and 2016 were analyzed. The search was performed in Scopus and Web of Science using the expressions "kidney segmentation" and "renal segmentation".

RESULTS

A total of 1528 articles were retrieved from the databases, and 95 articles were selected for this review. After analysis of the selected articles, the reviewed segmentation techniques were categorized according to their theoretical approach.

CONCLUSIONS

Based on the performed analysis, it was possible to identify segmentation approaches based on distinct image processing classes that can be used to accurately segment the kidney in images of different imaging modalities. Nevertheless, further research on kidney segmentation must be conducted to overcome the current drawbacks of the state-of-the-art methods. Moreover, a standardization of the evaluation database and metrics is needed to allow a direct comparison between methods.

Percutaneous nephrolithotomy: technique

Percutaneous nephrolithotomy (PCNL) is considered to be the first line of treatment for large renal stones. Though PCNL comes with higher morbidity, its efficacy is unbeaten by other minimally invasive modalities. However, potential complications, such as bleeding, occur. Improved skills and modifications of the procedure may reduce the probability of adverse outcomes. This article discusses the current trends and standards in PCNL technique with special focus on all important steps as positioning, access, instruments, dilation, disintegration, and exit, including outcomes, complication management, and training modalities.

The learning curve for access creation in solo ultrasonography-guided percutaneous nephrolithotomy and the associated skills

AIM

The aim of the current trial was to evaluate the learning curve of access creation through solo ultrasonography (US)-guided percutaneous nephrolithotomy (PCNL), and clarify the technical details of the procedure.

MATERIALS AND METHODS

We evaluated the first 240 solo US-guided PCNLs performed by one surgeon at our institution. The data including the puncture procedure, access characteristics, access-related complications and stone-free rates were assessed in four sequential groups.

RESULTS

The puncture duration and number of times decreased from a mean of 4.4 min and 2.1 times for the first 60 patients to 1.3 min and 1.2 times for the last 60 patients. There was a significant decrease from 3.7 min and 1.8 times for the 61th-120th patients to 1.5 min and 1.3 times for the 121th-180th patients. All of the access-related severe bleeding appeared in the first 120 patients, while perforations only occurred in the first 60 patients. The stone-free rates were 68.3, 83.3, 90.0, and 93.3% for the four sequential groups.

CONCLUSION

The increase in experience lead to an improvement in the puncture duration and times, which accompany with better stone-free rates and lower complications. We propose that 60 operations are sufficient to gain competency, and a cutoff point of 120 operations will allow the surgeon to achieve excellence in the solo US-guided PCNL.