Commentary

Laparoscopic pyeloplasty, performed for the treatment of ureteropelvic junction obstruction, has been shown to have success rates comparable to open pyeloplasty but without the associated postoperative morbidity of the larger open incision. It is known that laparoscopic suturing does require a higher level of skill, usually mastered over time with sufficient practice by urologic surgeons. However, in centers where the surgical volume is low, such advanced skills are difficult to attain, especially when working in the 2-dimensional view of the laparoscopic operative field, with the fulcrum effect of laparoscopic ports with only 4 degrees of freedom. Thus, robotic-assisted laparoscopic surgical intervention has gained rapid inroads on many urologic operations, especially where reconstruction is required.

The study by Lucas and colleagues is a large multicenter trial incorporating 759 pyeloplasty cases (274 laparoscopic and 465 robotic) for primary or recurrent ureteropelvic junction obstruction. The findings on multivariate analysis indicate that previous endopyelotomy and intraoperative crossing vessels reduced freedom from secondary procedures. These findings have been noted in earlier studies and would be an added incentive to consider avoidance of endopyelotomy for a primary UPJ obstruction. There was, however, an underlying trend on bivariate analysis (although not significant on multivariate analysis) that robotic-assisted surgery was superior to the pure laparoscopic approach to pyeloplasty with respect to perioperative complications, urinary leakage and overall improvement in postoperative symptoms and radiologic appearance.

As the authors correctly mention, an analysis of treatment modalities is difficult without a randomized, prospective comparison. After a medical center has spent a significant amount of money ($1.8 million) in purchasing a robotic unit, along with all the associated costs of the instrumentation, robot maintenance service contract and OR room development, there is not a strong incentive on the part of the surgeons and administrative personnel to encourage a randomized prospective study. However, the reality of the matter is that robotic surgery has been adopted very quickly without much population-based evidence demonstrating clearly superior outcomes compared to laparoscopic and open surgery.

Robotic surgery, almost across the spectrum of all surgical disciplines, is more expensive than laparoscopic and open interventions. As is briefly alluded to in the Lucas article, albeit with sparse numbers, robotic pyeloplasty is more expensive than the laparoscopic approach. The article by Yu and colleagues evaluates this further for multiple urologic procedures.

Subjects were identified to have undergone urologic robotic, laparoscopic and open urologic surgery from the Healthcare Cost and Utilization Project (HCUP) and Nationwide Inpatient Sample (NIS), sponsored by the Agency for Healthcare Research and Quality. Although interpretation of overall clinical effectiveness of such administrative data is not possible, simply looking at the financial costs alone indicates that robotic surgery is more expensive. Robotic-assisted pyeloplasty was found to be about $3500 more expensive for hospital costs alone than the laparoscopic approach (see Table 3 in article). This does not include surgeon fees and robotic system acquisition and maintenance costs.

Although we are reminded on a daily basis of our exorbitant, out of control, health care costs, I believe that the “robotic train has already left the station.” Reconstruction using the robot is easier, more surgeon-friendly and certainly more likely to be adopted by urologists with less laparoscopic experience. Residency programs are quickly incorporating training in this area and graduates are enthusiastically embracing this technology. As urologic surgeons, we have a responsibility to our patients to provide them with the best treatment approach within our technical abilities. It may be that the upfront higher costs of robotic intervention will be truly justified if the findings clearly show less postoperative morbidity, more rapid return to work and normal quality living, and surgical outcome as good or better than more traditional approaches.

Howard N. Winfield, M.D.

Commentary

This study measures radiation dose using a phantom model in a situation that simulates ureteroscopy; the same table with an integrated fluoroscopy unit which is used by the authors to treat their patients. The phantom model (using metal-oxide semiconductor field-effect transistor [MOSFET] detectors) is specific for allowing precise measurement of the radiation dose to different organs. The investigators found the highest exposures were to the small bowel and gallbladder. The mean ureteroscopy effective dose rate was found to be 0.024 mSv per second. Given a median fluoroscopy time of 46.95 seconds in their study patients, the calculated median effective dose was 1.13 mSv. This compares favorably to the radiation dose during a renal stone protocol CT scan (4.51 mSv) and is equivalent to that of a KUB.

This phantom model represents a male, non-obese patient. An acknowledged weakness of the study is the lack of data for obese patients and women. The exposure in obese patients could be quite different due to the settings required (and often set automatically) by the fluoroscopy system to provide an adequate image. Likewise, the dosage to the uterus and ovaries in women should be determined.

The authors used a traditional urology table with integrated fluoroscopy unit for this study. It would be useful to have the same precisely measured effective doses for modern portable C-arm fluoroscopy units. It would be interesting to see the difference (if any) between the various brands and models. Because the radiation source is below the table, portable C-arm fluoroscopy has the advantage of decreasing the level of scatter radiation exposure to operating room personnel. Another advantage of the use of a C-arm fluoroscopy unit is the ability to arc the C-arm into different positions. This allows not only the ability to improve visualization and localization of structures at different angles, but also permits “dose spreading” of the radiation dose over different areas of the skin. This is a technique used in many interventional fluoroscopic procedures to spread the radiation delivered to a larger area of skin, though it is less necessary for most ureteroscopic procedures when the fluoroscopy time is relatively short.¹

The investigators have precisely measured the effective dose of radiation our ureteroscopy patients experience, and it is reassuringly relatively low. Despite this, we should always practice the radiation safety principle of ALARA (As Low As Reasonably Achievable). There are practical methods to decrease the fluoroscopy time used during ureteroscopy, and these were studied by Baldwin and colleagues at Loma Linda University Medical Center.² Using a simple protocol including use of a laser guide, timing of fluoroscopy activation with respiration, and use of single pulse fluoroscopy mode for wire, stent and ureteroscope positioning, the investigators were able to reduce the mean fluoroscopy exposure by 82% (86.1 to 15.5 seconds).

References

1. Parry RA, Glaze SA, Archer BR. The AAPM/RSNA physics tutorial for residents. Typical patient radiation doses in diagnostic radiology. Radiographics 1999;19:1289–1302.

2. Greene DJ, Tenggadjaja CF, Bowman RJ, et al. Comparison of a reduced radiation fluoroscopy protocol to conventional fluoroscopy during uncomplicated ureteroscopy. Urology 2011;78:286–290.

Commentary

This is a landmark paper which presents a new cadaveric model for educating the urologist on the technique of image guided percutaneous approach for renal tumor ablation. The goals of this model are to increase urologists' understanding on various aspects of this technique, such as patient positioning and utilizing a radio-opaque targeting template to facilitate needle positioning. This proposed model and training structure would provide a firm foundation to master the technique for the urologist and possibly take over the procedure in the future from the interventional radiologist.

The process of acquiring this new technique could be similar to our earlier experience in learning renal access techniques where various training models have been created.^1–3 From a practical standpoint, the AUA already organized the first ablation course in November 2010.

References

1. Mishra S, Kurien A, Ganpule A, et al. Percutaneous renal access training: content validation comparison between a life porcine and a virtual reality (VR) simulation model. BJU Int 2010;106:1753–1756.

2. Mishra S, Kurien A, Patel R, et al. Validation of virtual reality simulation for percutaneous renal access training. J Endourol 2010;24;635–640.

3. Strohmaier WL, Giese A. Improved ex vivo training model for percutaneous renal surgery. Urol Res 2009;37:107–110.

Michael Y.C. Wong, M.B.B.S.

Anatomical variation between the prone, supine, and supine oblique positions on computed tomography: implications for percutaneous nephrolithotomy access. Duty B, Waingankar N, Okhunov Z, Ben Levi E, Smith A, Okeke Z, Arthur Smith Institute for Urology, North Shore-Long Island Jewish Health System, New Hyde Park, NY.

Urology 2012;79:67–71.

Objective: To determine anatomical variations between the prone, supine, and supine oblique positions that are likely to affect percutaneous renal access.

Material and Methods: Twenty patients underwent computed tomography urograms in the supine and prone positions. Twenty patients underwent supine oblique and prone scans. Mean nephrostomy tract length, maximum access angle, and anterior-posterior renal position were calculated.

Results: Mean nephrostomy tract length was shorter in the prone position (82.6 mm right kidney, 85.4 mm left kidney) compared with the supine position (108.3 mm right kidney, P < .001; 103.7 mm left kidney, P < .001). Prone tract length was also shorter than supine oblique tract length (86.1 mm vs 96.5 mm; P = .048). Mean maximum access angle was significantly greater (P = .018 right kidney; P = .007 left kidney) in the prone position (right kidney 99.7°, left kidney 104.0°) compared with the supine position (right kidney 87.7°, left kidney 89.4°). The same was true for the prone compared with the supine oblique position (75.8° vs 58.7°; P = .004). No difference was noted in anterior-posterior renal position between the supine and prone positions (20.3 mm vs 26.7 mm; P = .094) or supine oblique and prone positions (22.8 mm vs 15.6 mm; P = .45).

Conclusions: The prone position is associated with a significantly shorter nephrostomy tract length and more potential access sites, which may improve ease and safety of percutaneous renal access.

Copyright © 2012 Elsevier Inc. All rights reserved.

DOI: 10.1016/j.urology.2011.06.019

Commentary

There is an ongoing debate as to whether the supine or prone position is superior for percutaneous renal access procedures. Several earlier advocates for supine or modified supine positions demonstrated better patient factors like pulmonary-circulatory advantages, as well as decreased time in positioning the patient.^1–3

This carefully planned study clearly demonstrates that there are certain technical advantages gained, such as more potential renal access sites and shorter nephrostomy tract length, when the patient is placed in the prone position. All in all, it must be remembered that, for the most part, successful outcomes with acceptable morbidity for both positions are similar in the reported literature and the choice of position is largely determined by the attending urologist's preference and is a reflection of his/her past training.

References

1. Cracco CM, Scoffone CM. ECIRS (Endoscopic Combined Intrarenal Surgery) in the Galdakao-modified supine Valdivia position: a new life for percutaneous surgery? World J Urol 2011:29:821–827.

2. Atkinson CJ, Turney BW, Nobkle JG, et al. Supine vs prone percutaneous nephrolithotomy: an anesthetist's view. BJU Int 2011:108:306–308.

3. Duty B, Okhunov Z, Smith A, et al. The debate over percutaneous nephrolithotomy positioning: a comprehensive review. J Urol 2011:186:20–25.

Michael Y.C. Wong, M.B.B.S.

Commentary

Guidelines provide recommendations for improving clinical care based on the available information reviewed by an expert guideline panel. A panel develops recommendations based on not only published data but also their expertise. The EAU guidelines on laser technologies are impressive and complete in breadth and scope of review, and the recommendations reflect the experience and outcomes of many who are well versed in the field.

However, one weakness is that the guidelines do not explain the similarities and technological capabilities of each laser system and their impact on outcomes, nor the related chronological advancements made with each laser class. For example, in BPO laser treatments, laser classes are not well defined within categories, and it is not clear why potassium titanyl phosphate (KTP):neodymium (Nd) yttrium-aluminium-garnet (YAG) (second harmonic generation [SHG]) and LBO (lithium borate):Nd:YAG (SHG) lasers are placed in same categories, except that they are green. In the end, each is a 532 nm wavelength laser. Another example is the focus on power with holmium without an explanation as to why a 100-watt holmium should be different from an 80-watt holmium. The technical nuance of the various lasers and their impact on data is not well explained and can misguide a clinician who is not well versed in the technology.

With respect to lasers in general, wavelength, power, pulsing and other characteristics greatly impact the effect the laser will have on its target tissue and can greatly affect the technique utilized to get a desired effect. With holmium, the primary chromophore is water and the resulting laser effect is an intermittent to near continuous pulsing microexplosion of water that can break up a stone or tear or thermomechanically cut tissue while coagulating it. Lost in the guideline is that laser enucleation can be well performed at a setting lower than 80 watts, which is well within the capabilities of an 80-watt system, or even a 100-watt system. In fact, it can be argued that the thulium and holmium lasers are actually quite similar in effect due to the fact that they both function at about the 2100 wavelength and the big difference is the continuous wave and higher power of the thulium laser. Both are used to enucleate prostatic tissue in combination with a mechanical enucleation technique with the tip of a scope and assistance of a mechanical morcelator. It can be argued that the surgeon is the key ingredient with these techniques which are well known for their high learning curves.

With the KTP and LBO lasers, what is also lost in the guidelines is that the wavelength is 532 nm which is a “green” wavelength. Unlike 2100 nm, it goes though an aqueous/water solution without being absorbed and all its energy is absorbed in the target tissue. The pure vaporization technique is a different debulking technique than holmium lasers. The sequential development of KTP laser to LBO laser within each progressive advancing system was focused on maintaining the 532 nm wavelength with similar pulsing and laser characteristics for safety, but increasing the capable power of the laser system from 80 watts to 120 watts to 180 watts to increase efficiency at possibly the expense of safety. What is lost in the guidelines is that the user does not need to use 180 watts throughout the procedure and can also use an 80-watt equivalent setting during a procedure with a 180-watt laser to maintain the same safety factor. What needs to be emphasized is that 180 watts is obviously more powerful, but a trained user can get a safe and efficacious result with proper use.

Guidelines can provide a knee-jerk implementation to clinical care with the assumption that “if I read it I can apply it”. However, unlike medications, surgical treatment still requires experience and training to achieve the results intended or as published.

Finally, when reviewing these guidelines, it is assumed that randomized trials are the highest level of evidence. However, I would argue that certain non-randomized multicenter studies compared to single treatment center randomized studies are more reflective of real world outcomes. Naturally, multicenter studies with multiple surgeons provide the best real world data for what a technology can achieve in safety and efficacy with ease of implementation and use.

Alexis E. Te, M.D.

Surgical management of BPH in patients on oral anticoagulation: transurethral bipolar plasma vaporization in saline versus transurethral monopolar resection of the prostate. Delongchamps NB, Robert G, de la Taille A, Haillot O, Ballereau C, Saussine C, Kleinclauss F, Azzouzi AR, Lukacs B, Dumonceau O, Fourmarier M, Devonec M, Descazeaud A, Hôpital Cochin, APHP, Paris Descartes University, France.

Can J Urol 2011;18:6007–6012.

Introduction: To compare postoperative outcomes of patients on oral anticoagulation (OA) treated with transurethral plasma vaporization of the prostate in saline water (TUVis) and transurethral resection of the prostate (TURP).

Materials and Methods: Between January and December 2009, 111 patients on OA therapy were treated with either TURP or TUVis in eight centers. Types of OA and perioperative management were collected. Postoperative outcomes were statistically compared between the two groups.

Results: A total of 57 (51%) and 54 (49%) patients were treated with TURP and TUVis, respectively. Types of OA were not significantly different between the two groups, but bladder catheterization prior to surgery was more frequently observed in the TUVis group. Before surgery, 28 patients were treated with warfarin alone, 74 with a platelet aggregation inhibitor (PAI) alone, and 9 with a combination of both. PAI was withdrawn preoperatively in 50 patients. All treatments with warfarin were switched for heparin. Comparison of the two groups showed significantly less hemorrhagic complications after TUVis. Patients treated with TUVis experienced less bladder washouts (2% versus 18%, p = 0.008), less late hematuria (4% versus 19%, p = 0.02), and lower decrease of serum hemoglobin (mean decrease of 0.66 versus 1.47 g/dL, p = 0.02). Postoperative bladder catheterization and hospital stay were significantly shorter, whereas the rate of urinary retention was significantly higher. Three months after surgery, functional results were not significantly different between the two groups.

Conclusions: In patients on OA, TUVis led to significantly less bleeding, as well as shorter bladder catheterization and hospital stay than TURP.

Commentary

There are very few comparative studies regarding anticoagulation status on electrosurgical treatments for BPH and this study is one which provides data on the comparative advantage of what is essentially electrovaporization vs. electrosurgical cutting. However, it should be noted that these patients are off anticoagulants perioperatively, and are immediately placed back on oral anticoagulants after the procedure. They are not quite on anticoagulants during the procedure. That being stated, it is not surprising that bleeding is increased with standard TURP due to the thinner layer of coagulation that occurs with electrosurgical cutting vs. electrovaporization tissue removal. The range of anticoagulation status pre-, peri- and postoperatively varies from patient to patient, surgeon to surgeon, and technology to technology. Overall, it is most challenging to operate on actively anticoagulated patients. In each situation, it is prudent to minimize and normalize anticoagulation status perioperatively, and it is wise to counsel patients that the risk of bleeding is always higher when on an anticoagulant than off it. However, the risk of a significant thromoboembolic event needs to be weighed in this decision as well. This particular study focuses on patients who are not anticoagulated perioperatively, and the period of time of aggressive administering of anticoagulation postoperatively is the real issue. The greatest risk of bleeding occurs postoperatively in these situations. While short-acting anticoagulants are the standard postoperatively, the risk of bleeding is probably higher due to the ease with which short-acting agents can over-anticoagulate a patient before a blood level can be assessed.

Alexis E. Te, M.D.

GreenLight HPS− 120-W laser vaporization vs transurethral resection of the prostate (<60 mL): a 2-year randomized double-blind prospective urodynamic investigation. Pereira-Correia JA, de Moraes Sousa KD, Santos JB, de Morais Perpétuo D, Lopes-da-Silva LF, Krambeck RL, Muller VJ, Vaz FP, Servidores do Estado Federal Hospital - Urology, Rio de Janeiro, Brazil.

BJU Int 2012 Jan. 18 [epub ahead of print]

Study Type - Therapy (RCT) Level of Evidence 1b What's known on the subject? and What does the study add? Photovaporization of the prostate (PVP) is now challenging TURP as the standard treatment for lower LUTS caused by BPH. The learning curve for PVP is short and the main advantages of this method over TURP are a shorter period of hospitalization, a shorter period of postoperative vesical catheterization, lower levels of retrograde ejaculation, rare development of dilutional hyponatraemia syndrome, the lack of a need for postoperative vesical irrigation as a result of extremely low indices of postoperative haematuria, and the lack of a need to suspend anticoagulant medication for the surgery. Traditionally, comparisons of the effectiveness of TURP vs PVP have involved parameters such as peak flow urinary rate and post-void residual urine volume measurements, and have employed questionnaires such as the IPSS and the International Index of Erectile Function instruments. However, studies evaluating detailed urodynamic parameters remain scarce and non-comparative The present study compared postoperative, medium-term urodynamic parameters among patients receiving TURP and high-power PVP. We consider the present study to be distinctive because it involved a double-blind, detailed functional analysis of the vesical emptying stage over the course of 2 years, and did not simply comprise an evaluation of clinical parameters and uroflowmetrics. We saw a reduction of infravesical obstruction, as shown by the significant reduction of ≥20 cm H(2) O in the mean micturition pressure for the groups studied, as well as a significant reduction in bladder outlet obstruction index. Thus, the present data show that high-power PVP can achieve and maintain the same results as TURP over a period of 24 months regarding an aspect that is particularly important for maintaining vesical health (i.e. detrusor pressure during the evacuation of the bladder). Such urodynamic data describing the functional outcome of PVP are currently missing from the literature.

Objective:

• To assess the impact of GreenLight HPS(TM) 120-W (American Medical System Incorporation, Minnetonka, MN, USA) laser photovaporization of the prostate (PVP) compared to transurethral resection of the prostate (TURP) on urodynamic results, voiding function and sexual function.

Patients and Methods:

• In total, 20 men with intermediate/severe lower urinary tract symptoms as a result of benign prostatic hyperplasia (BPH) were randomly selected and equally divided into two groups: TURP and PVP.

Results:

• Mean IPSS scores were reduced in both groups, although they did not differ between the TURP and PVP groups.

Conclusions:

• Bladder storage symptoms may represent a major concern, although they are of limited duration in patients undergoing PVP.

© 2012 The authors. BJU International © 2012 BJU International.

DOI: 10.1111/j.1464-410X.2011.10878.x.

180-W XPS GreenLight laser therapy for benign prostate hyperplasia: early safety, efficacy, and perioperative outcome after 201 procedures. Bachmann A, Muir GH, Collins EJ, Choi BB, Tabatabaei S, Reich OM, Gómez-Sancha F, Woo HH, Department of Urology, University Hospital, Basel, Switzerland.

Eur Urol 2012;61:600–607.

Background: Photoselective vaporisation of the prostate has evolved from the GreenLight 80-W KTP powered laser to the latest 180-W XPS laser involving a MoXy fibre.

Objective: Evaluate the prevalence of perioperative complications and short-term outcome for the first time with the XPS laser in men with lower urinary tract symptoms (LUTS) due to benign prostatic enlargement (BPE).

Design, Setting, and Participants: Prospective data were collected from consecutive patients at seven centres worldwide during June 2010 and March 2011. Indication for surgery was based on the European Association of Urology and the American Urological Association guidelines. Patients receiving anticoagulants or those with retention were included and analysed separately.

Intervention: 180-W XPS GreenLight laser prostatectomy using the MoXy fibre.

Measurements: Standard parameters associated with transurethral prostate surgery and perioperative prevalence of surgery-associated problems or complications were documented.

Results and Limitations: A total of 201 patients were included in the study. Mean follow-up was 5.8 mo (standard deviation [SD]: 2.8; range: 1-12 mo). A quarter of the patients had a prostate volume ≥80ml. For prostates between 51 and 60ml, a mean of 300kJ (SD: 112) of energy was applied (lasing time: 35.0min; SD: 15). Statistically significant improvements were noted in all key parameters postoperatively. The prevalence of perioperative complications was low. Limitations of the study are short duration of follow-up and limited number of available patients for the functional follow-up.

Conclusions: The 180-W GreenLight XPS laser is a new effective treatment option with a low prevalence of perioperative complications for patients suffering from LUTS due to BPE.

Copyright © 2011 European Association of Urology. Published by Elsevier B.V. All rights reserved.

DOI: 10.1016/j.eururo.2011.11.041

Commentary

These two studies focus on 532 nm laser technology. The first study, by Pereira-Correia and colleagues, is interesting since it is one of the very few randomized, prospective studies comparing TURP that involves pre- and post-pressure flow urodynamic study in patients followed over two years. Often, there is a jockeying to see which is the superior procedure based on symptom improvement and noninvasive urodynamic parameters. However, TUR efficacy, either laser or electrosurgical, is predicated on effective debulking. If both techniques can achieve similar debulking effectiveness, then good results may depend on the surgeon achieving enough debulking. This is a subjective intraoperative assessment by the surgeon. In this particular study with small to medium size enlarged glands, it is not surprising to see little difference in urodynamic efficacy if the main goal is to remove tissue with whatever technology is applied. What is interesting is the increase in irritative symptoms and the extended time to resolution with lasers, suggesting that an inflammatory process may play an extended role with laser procedures due to increased coagulation and resulting coagulation necrosis that can occur with these procedures.

The second study, by Bachmann et al, focuses on the newest highest power reiteration of the 532 nm wavelenth laser which is capable of 180 watts power delivery. This is an important study since these lasers are basically replacing older GreenLight technology due to the increased range of power and flexibility during a procedure. While the study demonstrated good efficacy and safety in a multicenter study, it should be noted that each user involved in this study is a well-published and experienced 532 nm laser surgeon. How this higher power translates to equivalent safety profile with the novice or beginning user remains to be determined. However, it should be emphasize that while the laser is labeled as a 180 Watt laser, equivalent surgical effects to previous lasers can be attained by lowering its power. It may not be necessary to utilize the higher power, and one should start at a lower power before increasing it. While the goal of this study was to demonstrate equivalent safety and efficacy to previous lower power versions, it may be that the experienced user can better exercise caution with the higher power when needed to gain efficiency while maintaining safety. This safety profile may be less with an inexperienced user who may inappropriately utilize a higher power when not needed, and create an unintended effect such as more bleeding or a perforation. One must not forget the surgeon's role in the procedure.

Alexis E. Te, M.D.

Commentary

Gastrointestinal oxalate transport has a significant influence on the amount of oxalate excreted in urine. There is evidence that oxalate is both absorbed and secreted in the intestine. It is thought that secretion is a trans-cellular process and may be regulated in humans by a member of the SlC26 anion transporter family, Slc26a6 (PAT1, CFEX). Insect models provide insight into genetic and molecular mechanisms. These investigators demonstrated that a functional analogue of Slc26a6, Slc26a5 in the fruit fly and mosquito (dPrestin and AgPrestin) is up-regulated by OSR1 kinase which is controlled by WNK/SPAK signaling. Insight into these mechanisms may result in discovering methods to augment oxalate secretion which could potentially benefit patients with hyperoxaluria including those afflicted with primary hyperoxaluria.

Dean G. Assimos, M.D.

Association of randall plaque with collagen fibers and membrane vesicles. Khan SR, Rodriguez DE, Gower LB, Monga M, Department of Pathology, Immunology and Laboratory Medicine, Center for the Study of Lithiasis, College of Medicine, University of Florida, Gainesville, FL.

J Urol 2012;187:1094–1100.

Purpose: Idiopathic calcium oxalate kidney stones develop by calcium oxalate crystal deposition on Randall plaque. The mechanisms involved in Randall plaque formation are still unclear. We hypothesized that Randall plaque formation is similar to that of vascular calcification, involving components of extracellular matrix, including membrane bound vesicles and collagen fibers. To verify our hypothesis we critically examined renal papillary tissue from patients with stones.

Materials and Methods: We performed 4 mm cold cup biopsy of renal papillae on 15 patients with idiopathic stones undergoing percutaneous nephrolithotomy. Tissue was immediately fixed and processed for analysis by various light and electron microscopic techniques.

Results: Spherulitic calcium phosphate crystals, the hallmark of Randall plaque, were seen in all samples examined, including in interstitium and laminated basement membrane of tubular epithelium. Large crystalline deposits were composed of dark elongated strands mixed with spherulites. Strands showed banded patterns similar to collagen. Crystal deposits were surrounded by collagen fibers and membrane bound vesicles. Energy dispersive x-ray microanalysis and electron diffraction identified the crystals as hydroxyapatite. Few kidneys were examined and urinary data were not available on all patients.

Conclusions: Results showed that crystals in Randall plaque are associated with collagen and membrane bound vesicles. Collagen fibers appeared calcified and vesicles contained crystals. Crystal deposition in renal papillae may have started with membrane vesicle induced nucleation and grown by the further addition of crystals at the periphery in a collagen framework.

Copyright © 2012 American Urological Association Education and Research, Inc. Published by Elsevier Inc. All rights reserved.

DOI: 10.1016/j.juro.2011.10.125

Commentary

There is now abundant histological evidence that Randall plaque plays a role in the generation of idiopathic calcium oxalate stones. These investigators provide more detail of the structural interfaces. A search for the cellular and molecular mechanisms involved in the generation of this sub-epithelial crystalline complex is underway and should provide more insight into the pathophysiology of the most common type of kidney stone.

Dean G. Assimos, M.D.

Commentary

Recent reports of ”zero ischemia” partial nephrectomy continue to challenge minimally invasive urologists to limit warm ischemia during partial nephrectomy.¹ The initial description of ”zero ischemia” described pharmacologically induced hypotension during tumor resection, but now it has evolved to selective and superselective dissection and clamping of segmental and subsegmental branches of the renal vasculature.² The ability for such complex hilar dissection may not be readily applicable to the general urologist. What if you could accomplish the same type of superselective occlusion without the need for hilar dissection?

Harty et al describe their initial animal studies involving the use of Lumagel to provide intraarterial temporary occlusion to select vessels. Lumagel is a reverse thermosensitive polymer that can be administered fluoroscopically into segmental and subsegmental renal artery branches to produce temporary blood flow interruption to renal tissue targeted for excision, while maintaining normal flow to the spared nephrons. Lumagel is a mixture of poloxamer 407 and iohexol (Food and Drug Administration-approved contrast agent) in aqueous solution. Lumagel exists as a low viscosity liquid when cool (20°C) and rapidly increases in viscosity by a factor of 106 on warming. In its high viscosity state, this liquid acts as a gel. On intravascular injection, body temperature causes the injected polymer to suddenly form a hemostatic, intraluminal ”plug.” On recooling, the Lumagel reverts to its low viscosity state, dissolves in the flowing blood, and is excreted unmetabolized in the urine.

A total of 10 animals (7 pigs and 3 calves) were used to compare Lumagel (n = 8) to hilar clamping (n = 2) during partial nephrectomy. Using Lumagel, targeted blood flow interruption was achieved for up to 30 minutes, and circulation to the uninvolved renal tissue was maintained. Estimated blood loss was negligible except in two cases—one in which a vessel was not selected for occlusion near the resection site, and another in which the guidewire passed through the vessel wall. The interval to complete flow return, as determined by direct visualization of the kidney and its corresponding angiogram, averaged 7 and 2.5 minutes for Lumagel and arterial clamping, respectively. Lumagel provides reliable and reproducible intraluminal blood flow interruption and flow restoration in both main and segmental renal arteries.

In theory, this technology would allow temporary superselective occlusion to perform a partial nephrectomy resection without the need of hilar dissection. That could potentially reduce operative time and risk to the major hilar vessels. In transferring this technique to humans, however, the clinical scenario is more difficult. Patients would need to have a femoral line placed in the supine position prior to going into a lateral decubitus position. Fluoroscopy is also required, which is difficult to perform when in the flank position. Potential damage to the vessels may also occur during canalization and deposition of the Lumagel. Nonetheless, the work with this type of technology is exciting and will hopefully provide us with another option for minimizing ischemia during laparoscopic/robotic partial nephrectomy.

References

1. Gill IS, Eisenberg MS, Aron M, et al. ”Zero ischemia” partial nephrectomy: novel laparoscopic and robotic technique. Eur Urol. 2011;59:128–134.

2. Ng CK, Gill IS, Patil MB, et al. Anatomic renal artery branch microdissection to facilitate zero-ischemia partial nephrectomy. Eur Urol 2012;61:67–74.

David A. Duchene, M.D.

Focused ultrasound to expel calculi from the kidney. Shah A, Harper JD, Cunitz BW, Wang YN, Paun M, Simon JC, Lu W, Kaczkowski PJ, Bailey MR, Department of Urology, University of Washington, Seattle, WA.

J Urol 2012;187:739–743.

Purpose: A persistent stone burden after renal stone treatment may result in future patient morbidity and potentially lead to additional surgery. This problem is particularly common after treatment of lower pole stones. We describe a potential noninvasive therapeutic option using ultrasound waves to create a force sufficient to aid in stone fragment expulsion.

Materials and Methods: Human stones were implanted by retrograde ureteroscopy or antegrade percutaneous access in a live porcine model. The calibrated probe of a system containing ultrasound imaging and focused ultrasound was used to target stones and attempt displacement. To assess for injury an additional 6 kidneys were exposed for 2 minutes each directly to the output used for stone movement. Another 6 kidneys were exposed to more than twice the maximum output used to move stones. Renal tissue was analyzed histologically with hematoxylin and eosin, and nicotinamide adenine dinucleotide staining.

Results: Stones were moved to the renal pelvis or ureteropelvic junction by less than 2 minutes of exposure. Stone velocity was approximately 1 cm per second. There was no tissue injury when tissue was exposed to the power level used to move stones. Localized thermal coagulation less than 1 cm long was observed in 6 of 7 renal units exposed to the level above that used for ultrasonic propulsion.

Conclusions: Transcutaneous ultrasonic propulsion was used to expel calculi effectively and safely from the kidney using a live animal model. This study is the first step toward an office based system to clear residual fragments and toward use as a primary treatment modality in conjunction with medical expulsive therapy for small renal stones.

Copyright © 2012 American Urological Association Education and Research, Inc. Published by Elsevier Inc. All rights reserved.

DOI: 10.1016/j.juro.2011.09.144

Commentary

Small ”insignificant” residual stones after surgical nephrolithiasis management have been shown to usually not be ”insignificant.”¹ This is especially true for lower pole stone fragments which may be difficult to pass. Besides percussion, diuresis and inversion therapy (all of which have minimal success), not many other techniques exist to facilitate the movement of lower pole stone fragments from the kidney.

Shah et al demonstrate both a novel concept and technique to help move stone fragments from the kidney. They describe a relatively noninvasive therapeutic option using ultrasound waves to create a force sufficient to aid in stone fragment expulsion.

Using a porcine model, human kidney stones were implanted into 6 pig kidneys and a specially calibrated ultrasound probe system (containing ultrasound imaging capabilities and a focused ultrasound energy feature) was used to target stones and attempt displacement. To assess the safety of the system, an additional 6 kidneys were directly exposed to the output energy used for stone movement (325W/cm2) for 2 minutes, and another 6 kidneys were directly exposed to more than twice the maximum output used to move stones (1900W/cm2). Renal tissue was analyzed histologically with hematoxylin and eosin, and nicotinamide adenine dinucleotide staining.

The stones were moved in all the porcine models to the renal pelvis or ureteropelvic junction by less than 2 minutes of ultrasound exposure. Stone velocity was approximately 1 cm per second. There was no tissue injury when tissue was exposed to the power level used to move stones. However, localized thermal coagulation less than 1 cm long was observed in 6 of 7 renal units exposed to the energy level above that used for ultrasonic propulsion. Overall, transcutaneous ultrasonic propulsion was used to expel calculi effectively and safely from the kidney using a live animal model.

This technique shows great promise as an essentially painless procedure that could be utilized in the clinic to propel fragments out of the kidney. It could also push a ureteropelvic stone back into the renal pelvis in the setting of obstruction to temporarily avoid the need to place a stent or nephrostomy tube. The pediatric population (in which radiation exposure is of greater concern) is an ideal patient group since the ultrasound energy emits no radiation. The drawbacks to the technology, however, are that small stones (the ”insignificant” fragments) may not be well-visualized ultrasonically for propulsion. Only certain ultrasound angles produce the propulsion, so stone orientation with the infindibulum of the kidney may present challenges. Also, as noted at higher ultrasound energies, potential renal damage will continue to be a concern until more histological and functional studies are performed.

Reference

1. Raman JD, Bagrodia A, Gupta A, et al. Natural history of residual fragments following percutaneous nephrostolithotomy. J Urol 2009;181:1163–68.

David A. Duchene, M.D.

Commentary

These two recently published articles elucidate the factors associated with complications during renal ablative therapies. The data from these studies should help those performing ablative therapy to refine their selection factors for patients being evaluated for this form of treatment, to predict possible adverse events in hopes of minimizing the risk of their occurrence, and to improve patient counseling and the informed consent process.

The study by Castle et al, a retrospective 10-year single-institution study, identified preoperative factors associated with both surgical complications and successful diagnostic renal biopsy during both laparoscopic and percutaneous radiofrequency ablation (RFA). The study was designed to aid in counseling patients before treatment. In this study, 124 tumors were treated laparoscopically and 211 percutaneously. In 5.5% of the 335 cases, biopsies were nondiagnostic, and complications occurred in 30.7% of procedures. Multivariable analysis showed that the percutaneous approach increased the likelihood of nondiagnostic biopsy nearly 5-fold (odds ratio [OR], 5.1; 95% confidence interval [CI], 1.2-22.0; P = 0.032). Increased tumor size as well as multiple ablations increased the risk of major complications. The surgeon's experience and tumors located close to the urinary collecting system increased the risk of any complications. Larger tumor sizes, multiple ablations, and deeper tumors carried a higher risk of major complications. The authors concluded that these data can help in counseling patients about the risk of nondiagnostic biopsy.

The study by Atwell et al describes experience with RFA and cryoablation performed from 2000 to 2010 at the Mayo Clinic. A total of 573 ablation procedures (254 RFA and 311 cryoablation, with 8 having had both forms) for treatment of 633 tumors were performed in 533 patients. The authors found from their prospectively collected data that of the 573 procedures, 63 (11%) were associated with complications, 6.6% of which were determined to be major based on the Clavien-Dindo grade 2-4 classification, and there were no deaths. Although there were no statistical differences in major complications between cryoablation and RFA (p = 0.15), the difference in the overall rates was notable (cryoablation 7.7%, RFA 4.7%), so it is possible that the number of events was too small to draw a statistical conclusion.

Interestingly, however, the authors showed that specific complications were associated with the specific modality used. For example, cryoablation was associated more with bleeding and hematuria, which were quite common. The bleeding during cryoablation was found to be associated with age, larger tumor size, number of probes used, and central location of the tumor. Logistic regression models were developed, and all of the above factors remained positively correlated. With use of backward selection, two models were identified: age and size of tumor, as well as age and number of probes. These remained as independent factors. Thus, for every increase in age of 1 year, the odds of a defined bleeding complication increased slightly (OR, 1.11; 95% CI, 1.03-1.94; P = 0.006). For every 1-cm increase in tumor size, the odds of a bleeding complication increased nearly 2-fold (OR, 2.04; 95% CI, 1.50-2.79; P < 0.001). Specifically with RFA procedures, the most common complications were associated with nerve and urothelial injury. Of the 10 patients with nerve injuries, only 1 had a deficit for more than 6 months. Most of these injuries manifested as sensory deficit pain paresthesias or numbness in a dermatomal pattern. Flank muscle laxity was also observed. Of the 6 patients with urothelial injury, chronic strictures developed in 5 at the ureteropelvic junction. The authors concluded that complications associated with percutaneous renal ablation are infrequent but that recognition of the potential complications allows for optimization of periprocedural care.

These two articles highlight some of the improvements being made in identifying risk factors for complications associated with specific procedures. Age appears to be an independent predictor of local complications; this is of interest because previous reports of surgical procedures have shown that age, by itself, is not an independent predictor of complications, but that increasing age is associated with a higher rate of comorbidities.¹ In these previous studies, complications are associated with comorbidities; this association was not assessed in the two articles addressed in this review. Nevertheless, these two informative articles show how we can better tailor our approaches for higher-risk patients undergoing ablative therapy and more optimally counsel these patients during the informed consent process. Hemorrhagic complications are associated with larger and deeper tumors, procedures in older patients, and use of cryoablation. RFA is associated more with neuropathic and urothelial complications. Overall, major complications also seem to be associated with surgeon experience and multiple ablations.

Reference

1. Matin SF, Abreu S, Ramani A, et al. Evaluation of age and comorbidity as risk factors after laparoscopic urological surgery. J Urol 2003;170:1115–1120.

Surena F. Matin, M.D.