Randomized controlled, multicentre clinical trial comparing a dual-probe ultrasonic lithotrite with a single-probe lithotrite for percutaneous nephrolithotomy.

OBJECTIVES: • To compare the Cyberwand (Gyrus/ACMI, Southborough, MA, USA), a dual-probe ultrasonic lithotrite, with a single-probe ultrasonic lithotrite. • The Cyberwand incorporates coaxial high- and low-frequency ultrasonic probes that work synergistically. PATIENTS AND METHODS: • An institutional review board-approved, multicentre, randomized controlled trial to compare the Cyberwand to the Olympus LUS-II (Olympus America, Inc., Melville, NY, USA) single-probe lithotrite was performed. • Patients undergoing a percutaneous nephrolithotomy (PCNL) with a target stone > 2 cm in diameter were eligible for the study. • The primary outcome was the time to removal of the targeted stone. RESULTS: • A total of 57 PCNLs were performed after randomization: 25 Cyberwand and 32 LUS-II. • There was no difference (P > 0.05) observed between the two devices for target stone surface area (Cyberwand 526.6 cm³ vs LUS-II 540.1 cm³), time to clearance of target stone (Cyberwand 15.8 min vs LUS-II 14.2 min) and target stone clearance rate (Cyberwand 61.9 mm²/min vs LUS-II 75.8 mm²/min). • Of the patients with stone analysis, hard stones (calcium oxalate monohydrate, brushite and cystine) were noted in 14 (56.0%) of the 25 Cyberwand and 18 (62.1%) of the 29 LUS-II patients. • Fifteen of the 25 (60.0%) Cyberwand and 20 of the 32 (62.5%) LUS-II patients were stone-free after the initial PCNL. • Those patients not rendered stone-free went on to receive a secondary PCNL. • Device malfunction occurred in eight of 25(32.0%) Cyberwand and five of 32 (15.6%) LUS II patients. • Complications were similar in both treatment groups. CONCLUSION: • No appreciable difference between the dual-probe Cyberwand and the standard ultrasonic Olympus LUS-II lithotrites can be identified.

In idiopathic calcium oxalate stone-formers, unattached stones show evidence of having originated as attached stones on Randall's plaque.

OBJECTIVE: To analyse the structure and composition of unattached stones in idiopathic calcium oxalate (CaOx) stone-formers (ICSF) and compare them to attached stones from the same cohort, to investigate whether there is more than one pathogenic mechanism for stone formation in ICSF. PATIENTS AND METHODS: ICSF undergoing percutaneous nephrolithotomy or ureteroscopy for the treatment of nephrolithiasis gave consent to participate in this study. All accessible renal papillae were endoscopically imaged using a digital endoscope. All stones were removed and determined by the operating surgeon to be attached or unattached to the underlying papilla. Micro-computed tomography (micro-CT), which provides three-dimensional analysis of entire stones, was used to compare the structure and composition of attached and unattached stones. RESULTS: Of 115 stones collected from nine patients (12 renal units), only 25 stones were found not to be attached to renal papillae. Of these 25 stones, four were lost and 12 showed definite morphological evidence of having been attached to tissue, probably having been displaced from papillae during access. For the remaining nine stones, micro-CT analysis showed at least one internal region of calcium phosphate within each of these unattached CaOx stones, i.e. the internal structure of the unattached stones is consistent with their having originated attached to Randall's plaque, and then having become detached but retained in the kidney, with new layers of CaOx eventually covering the original attachment site. CONCLUSIONS; Micro-CT analysis supports the hypothesis that in ICSF, both attached and unattached stones occur as a result of a common pathogenic mechanism, i.e. in this type of stone former, CaOx stones, even those not showing morphology that betrays attachment, all originate attached to interstitial plaque on the renal papilla.

A formal test of the hypothesis that idiopathic calcium oxalate stones grow on Randall's plaque.

OBJECTIVE: To confirm that more than half of all idiopathic calcium oxalate (CaOx) stones grow on interstitial plaque, as CaOx stones can grow attached to interstitial apatite plaque but whether this is the usual mechanism of stone formation is uncertain. PATIENTS AND METHODS: In nine idiopathic CaOx stone formers (ICSF) undergoing percutaneous nephrolithotomy or ureteroscopy all accessible renal papillae were endoscopically imaged using a digital endoscope. All stones were removed intact, and recorded by the operating surgeon as being attached or unattached; for all attached stones the surgeon determined if the site of attachment was to plaque. This determination was further verified by reviewing the intraoperative video record, and only instances where plaque was reliably seen on video were used for analysis. Surgical observations were further validated by a combination of microcomputed tomographic analysis and papillary biopsy. The results were analysed statistically using fixed-sample testing and group sequential sampling. RESULTS: The nine patients had a total of 115 stones, primarily CaOx; 90 stones were attached. Of these, 81 were attached to plaque; surgeons could not visualize the site of attachment with sufficient clarity to judge in the other nine cases. Based on these data, the final point estimate for the number of stones attached to plaque was 0.754 (95% confidence interval 0.575-0.933; P = 0.013). CONCLUSIONS: In ICSF most stones grow attached to papillae, on plaque, so growth on plaque is the main mechanism for stone formation in this very common group of patients.

A new world revealed: early experience with digital ureteroscopy.

PURPOSE: The latest digital ureteroscope, the DUR-D (Gyrus ACMI Inc., Southborough, Massachusetts) offers image quality that greatly exceeds current analog image capabilities. The purpose of this report was to document the applicability of this device in studying the earliest stages of stone formation. MATERIALS AND METHODS: Symptomatic patients with nephrolithiasis (less than 1 cm in diameter) were prospectively enrolled and their renal papilla digitally mapped prior to stone removal. Recovered stones were photographed and analyzed using micro-computerized tomography. If the procedure could not be completed with the DUR-D, a conventional ureteroscope was used. Minors, pregnant patients and those with systemic disorders were excluded. RESULTS: Eight patients (10 renal units), 2 cystine and 6 calcium oxalate stone formers, were studied with a mean age of 50.1 years. Excellent images were collected for all papilla except in 2 cases; a proximal ureteral stricture and acute angulation of the lower pole collecting system, respectively. There were no mechanical device failures. Of the 10 renal units 7 had stents postoperatively and there were no patient complications. CONCLUSIONS: The ease of use and high quality images of digital ureterorenoscopy will allow the documentation of the earliest stages of calcium oxalate stone formation and, thereby, advance our understanding of the pathogenesis of calcium oxalate stone formation.

Holmium laser enucleation of the prostate--outcomes independent of prostate size?

PURPOSE: Generally treatment decisions for benign prostatic hyperplasia are based on prostate size and surgeon experience. Prostates greater than 100 gm often require open surgery. However, less invasive options are available. Randomized, controlled trials have demonstrated that holmium laser enucleation of the prostate is a viable and effective treatment for benign prostatic hyperplasia. We examined the outcome of holmium laser enucleation of the prostate based on prostate size. MATERIALS AND METHODS: We retrospectively reviewed the records of all patients in our institutional review board approved database who underwent holmium laser enucleation of the prostate from January 1999 to October 2006. Patients were divided into 3 cohorts based on preoperative transrectal ultrasound prostate measurements, including less than 75, 75 to 125 and more than 125 gm. Patients with prostate cancer were excluded from study. Demographic, laboratory, operative, preoperative and postoperative data were obtained. RESULTS: As prostate size increased, so did prostate specific antigen, and the urinary retention and enucleation rates. Hospitalization, catheterization, preoperative and postoperative outcomes were similar among the groups. On linear regression the decrease in prostate specific antigen highly correlated with the amount of tissue removed (p <0.0001). The complication rate was similar among the treatment groups. All patients did equally well in terms of postoperative urinary function independent of prostate size. CONCLUSIONS: Holmium laser enucleation of the prostate is a safe and effective minimally invasive treatment for benign prostatic hyperplasia. It improved patient prostate specific antigen, American Urological Association symptom score and maximum urinary flow rate independent of the amount of benign prostatic hyperplasia present. Our results demonstrate the advantage of holmium laser enucleation of the prostate to treat all prostates regardless of size with favorable and equivalent outcomes.

Prospective randomized trial comparing shock wave lithotripsy and ureteroscopy for lower pole caliceal calculi 1 cm or less.

PURPOSE: The optimal management of lower pole renal calculi is controversial. We compared shock wave lithotripsy (SWL) and ureteroscopy (URS) for the treatment of patients with small lower pole stones in a prospective, randomized, multicenter trial. MATERIALS AND METHODS: A total of 78 patients with 1 cm or less isolated lower pole stones were randomized to SWL or URS. The primary outcome measure was stone-free rate on noncontrast computerized tomography at 3 months. Secondary outcome parameters were length of stay, complication rates, need for secondary procedures and patient derived quality of life measures. RESULTS: A total of 67 patients randomized to SWL (32) or URS (35) completed treatment. The 2 groups were comparable with respect to age, sex, body mass index, side treated and stone surface area. Operative time was significantly shorter for SWL than URS (66 vs 90 minutes). At 3 months of followup 26 and 32 patients who underwent SWL and URS had radiographic followup that demonstrated a stone-free rate of 35% and 50%, respectively (p not significant). Intraoperative complications occurred in 1 SWL case (unable to target stone) and in 7 URS cases (failed access in 5 and perforation in 2), while postoperative complications occurred in 7 SWL and 7 URS cases. Patient derived quality of life measures favored SWL. CONCLUSIONS: This study failed to demonstrate a statistically significant difference in stone-free rates between SWL and URS for the treatment of small lower pole renal calculi. However, SWL was associated with greater patient acceptance and shorter convalescence.

Pre-percutaneous nephrolithotomy opacification for caliceal diverticular calculi.

Caliceal diverticula harbor calculi in as many as 50% of cases. Such stones rarely pass spontaneously. Various stone-removal techniques have been used, with percutaneous techniques generally having the best results. In patients with nonradiopaque stones or in whom the diverticulum does not opacify when contrast is instilled retrograde or by intravenous urogram, contrast can be instilled directly into the cavity with CT or ultrasound guidance. Three such cases are described, with good results.

Mini-laparoscopy-assisted placement of Tenckhoff catheters: an improved technique to facilitate peritoneal dialysis.

BACKGROUND AND PURPOSE: Despite its overall efficacy and patient satisfaction with it, peritoneal dialysis has a history of significant complications, which has contributed to the evolution in the technique from open laparotomy to minimally invasive placement of the catheters. Our goal was twofold: (1) to review our early experience with a technique of mini-laparoscopy-assisted (MLA) placement of dialysis catheters compared with open placement and (2) to demonstrate that urologists are able to provide a satisfactory procedure while concurrently developing and maintaining laparoscopic skills within a residency training program. PATIENTS AND METHODS: The charts of the first 14 consecutive patients who underwent MLA placement of Tenckhoff dialysis catheters by a single surgeon (LCM) from January 1, 2000, through March 31, 2001, were reviewed. Postoperative narcotic analgesia, length of hospital stay, operative times, days until cycling, and rates of leakage, infection, and malfunction necessitating removal of catheters were compared with the corresponding data from 12 consecutive patients who underwent traditional open placement during the same time period. A telephone survey was performed to corroborate and supplement the findings from the chart review. RESULTS: Differences in complications necessitating catheter removal were not significant. The difference in the mean operative times of 41.7 minutes in the MLA group and 55.7 minutes for open placement was statistically significant. Postoperatively, the MLA group used less narcotic analgesia, had shorter hospital stays, and returned earlier to usual activities. The incidence of leakage after catheter placement was greater in the open group, although this difference was not statistically significant. CONCLUSIONS: The MLA technique of dialysis catheter placement appears to have similar or greater efficacy than the open technique. It is a viable teaching procedure, and with reusable 3-mm ports and shorter operative times, it is cost efficient as well.

The presence of horseshoe kidney does not affect the outcome of percutaneous nephrolithotomy.

BACKGROUND AND PURPOSE: Large or complex calculi within a horseshoe kidney can present a challenge because many cases are associated with other aberrant anatomy. We performed a study to define the outcome of patients with a horseshoe kidney who were treated with percutaneous nephrolithotomy (PNL). PATIENTS AND METHODS: From August 1999 to February 2007, 44 PNLs were performed in 35 patients for calculi within a horseshoe kidney. Mean age was 55.4 years. Parameters evaluated to assess the outcomes of PNL included presenting symptoms, stone burden, location of access, stone-free rate, need for secondary intervention, length of stay (LOS), complication rate, stone analysis, and metabolic data. RESULTS: The average stone burden per kidney was 2.59 cm (range 1-6.2 cm). Single percutaneous access was used in 97.7%. Location of the access tract was upper pole (82.2%), interpolar (13.4%), and lower pole (4.4 %). Flexible nephroscopy was performed in all patients. The stone-free rate after primary PNL was 84.1%. Second-look nephroscopy was performed in five kidneys. Overall stone-free rate was 93.2%. Average LOS was 1.92 days (range 1-4 d). Overall complication rate was 14.3%. Stone analysis revealed predominantly calcium stones, and metabolic abnormalities were demonstrated in all patients with 24-hour urine studies. CONCLUSIONS: PNL is the treatment of choice for large and/or complex stones. The presence of a horseshoe kidney does not affect the outcome of PNL. Upper pole access is usually preferred, and flexible nephroscopy is essential to maximize stone-free rates. SA and metabolic data support the premise that calculus formation is a metabolic event.

Changing composition of renal calculi in patients with neurogenic bladder.

PURPOSE: Renal calculi are a significant source of morbidity for patients with neurogenic bladder. Calculi from patients with NB have traditionally been composed primarily of struvite and carbonate apatite secondary to chronic urea-splitting bacteriuria. In the current era there have been great improvements in the urological rehabilitation of patients with NB. We defined the composition of renal calculi in a contemporary cohort of patients with NB due to spinal cord injury or myelomeningocele who underwent percutaneous nephrolithotomy. MATERIALS AND METHODS: We performed a retrospective evaluation of all patients with NB due to SCI or MM who underwent PNL between January 2002 and January 2005. RESULTS: A total of 32 patients with NB (14 with SCI, 18 with MM) underwent PNL in this period. Stones were infectious in etiology in 37.5% (12 struvite/carbonate apatite) and metabolic in 62.5% (1 uric acid, 2 calcium oxalate monohydrate, 2 brushite, 6 hydroxyapatite, 9 mixed hydroxyapatite/calcium oxalate). All patients with struvite calculi were infected with urea-splitting bacteria on preoperative urine culture. CONCLUSIONS: Patients with neurogenic bladder are traditionally thought to harbor infection related calculi. These data demonstrate that many contemporary patients will be found to have calculi of a metabolic etiology. Although patients with NB still have renal calculi, advances in urological treatment may have affected the composition of their calculi, as metabolic stones are becoming more commonly identified. When metabolic components are identified, stone activity may be attenuated with appropriate metabolic evaluation, pharmacological therapies and dietary modifications.

Percutaneous nephrolithotomy for ectopic kidneys: over, around, or through.

OBJECTIVES: The treatment of patients with complex urolithiasis in ectopic kidneys can be challenging. Because the location of an ectopic kidney can vary, each case requires a unique and, at times, unconventional approach. We reviewed the techniques we have developed to treat such patients, including laparoscopic-assisted tubeless, transhepatic, and transiliac percutaneous nephrolithotomy (PNL). METHODS: We performed a retrospective analysis of all patients with congenital pelvic kidneys who underwent PNL at our institution. Six patients underwent laparoscopic-assisted PNL, one underwent transiliac PNL, and one underwent transhepatic PNL. All laparoscopic-assisted procedures were performed tubeless, with an internalized ureteral stent placed at the conclusion of the procedure. RESULTS: All patients underwent successful PNL. On computed tomography, performed on the morning of postoperative day 1, all patients who underwent laparoscopic-assisted PNL were stone free. The patients who underwent transiliac PNL and transhepatic PNL required secondary procedures to attain a stone-free status. The mean length of hospitalization was 3 days for the laparoscopic-assisted cohort, 1 day for the transhepatic patient, and 3 days for the transiliac patient. CONCLUSIONS: For the patient with a large or complex stone burden in an ectopic kidney, laparoscopic-assisted PNL is the optimal treatment. Performing such a procedure tubeless may be associated with a reduced hospital stay. For those patients with a hostile peritoneal cavity owing to prior surgical exploration, consideration should be given to a more individualized approach.

Endoscopic evidence of calculus attachment to Randall's plaque.

PURPOSE: It has been proposed that calcium oxalate calculi begin as small stones attached to the renal papillae at sites of Randall's plaque. However, no study has investigated the prevalence of attached stones in calcium oxalate stone formers or the relationship between stone attachment site and Randall's plaque. In this study we used endoscopic examination of renal papillae in stone formers undergoing percutaneous nephrolithotomy to investigate both issues. MATERIALS AND METHODS: Idiopathic calcium oxalate stone formers undergoing PNL for stone removal were enrolled in this study. Multiple papillae were examined and images were recorded by digital video. The presence or absence of papillary plaque and attached stones was noted, as was the site of stone attachment. RESULTS: In 23 patients, 24 kidneys and 172 renal papillae were examined. All kidneys were found to have papillary plaque and 11 of the patients had attached stones. Most papillae (91%) contained plaque. CONCLUSIONS: The prevalence of attached stones in calcium oxalate stone formers (48%) is greater than that previously reported for the general population. Attachment appears to be on Randall's plaque. The high prevalence of attached stones and the appearance of the attachment site are consistent with a mechanism of calcium oxalate stone formation in which stones begin as plaque overgrowth.

Stone formation is proportional to papillary surface coverage by Randall's plaque.

PURPOSE: Randall's plaques are common in calcium oxalate (CaOx) stone formers (SF). Plaque coverage correlates directly with urine calcium excretion and inversely with urine volume. We hypothesize that plaque coverage should increase proportionally with increasing stone number. We measured plaque areas in idiopathic CaOx stone formers and nonstone formers (NSF), and identified significant relationships with quantified stone histories. MATERIALS AND METHODS: A total of 13 SFs and 4 control NSFs underwent nephroscopic papillary mapping with representative still images and MPEG (Moving Pictures Experts Group) movies used to identify plaque and papillary borders. Stone histories were obtained through patient interviews, and from medical records and radiographs. The relationship of plaque coverage to clinical stone events was assessed by general multivariate linear modeling. Log transformation normalized the distribution of percent plaque coverage and stone number. RESULTS: Plaque surface area in SFs differed significantly from that in NSFs (p <0.0001). The duration of stone disease and the log transformed percent plaque coverage correlated significantly with the number of stones (0.677 and 0.620, p = 0.003 and 0.008, respectively). On multivariate analysis and correcting for the duration of stone disease total percent plaque coverage correlated significantly with the number of stones (R = 0.496, p = 0.05). Disease duration and plaque coverage did not correlate significantly (p = 0.257). CONCLUSIONS: Percent plaque coverage directly correlates with the number of stones formed even when corrected for the duration of stone disease. However, plaque coverage does not correlate with the duration of stone disease. These results support the hypothesis that the pathogenesis of CaOx stones begins with Randall's plaques.

Prospective, randomized trial comparing shock wave lithotripsy and ureteroscopy for lower pole caliceal calculi 1 cm or less.

PURPOSE: The optimal management of lower pole renal calculi is controversial. We compared shock wave lithotripsy (SWL) and ureteroscopy (URS) for the treatment of patients with small lower pole stones in a prospective, randomized, multicenter trial. MATERIALS AND METHODS: A total of 78 patients with 1 cm or less isolated lower pole stones were randomized to SWL or URS. The primary outcome measure was stone-free rate on noncontrast computerized tomography at 3 months. Secondary outcome parameters were length of stay, complication rates, need for secondary procedures and patient derived quality of life measures. RESULTS: A total of 67 patients randomized to SWL (32) or URS (35) completed treatment. The 2 groups were comparable with respect to age, sex, body mass index, side treated and stone surface area. Operative time was significantly shorter for SWL than URS (66 vs 90 minutes). At 3 months of followup 26 and 32 patients who underwent SWL and URS had radiographic followup that demonstrated a stone-free rate of 35% and 50%, respectively (p not significant). Intraoperative complications occurred in 1 SWL case (unable to target stone) and in 7 URS cases (failed access in 5 and perforation in 2), while postoperative complications occurred in 7 SWL and 7 URS cases. Patient derived quality of life measures favored SWL. CONCLUSIONS: This study failed to demonstrate a statistically significant difference in stone-free rates between SWL and URS for the treatment of small lower pole renal calculi. However, SWL was associated with greater patient acceptance and shorter convalescence.

Laparoscopic excision of a solitary renal cell carcinoma metastasis to the contralateral perirenal adipose tissue.

Metastasis of renal cell carcinoma to the contralateral perirenal fat is a very rare occurrence. We report a case of a synchronous, solitary perirenal metastasis excised laparoscopically 2 years after initial, open radical nephrectomy.

Bilateral hand-assisted laparoscopic nephrectomy for autosomal dominant polycystic kidney disease using a single midline HandPort incision.

OBJECTIVES: To present one of the first known series of bilateral, transperitoneal laparoscopic nephrectomy for autosomal dominant polycystic kidney disease using a hand-assisted technique by way of a single, midline HandPort incision. Synchronous, bilateral nephrectomy for autosomal dominant polycystic kidney disease is an infrequently performed procedure, with only a few reports using laparoscopy. METHODS: We retrospectively reviewed the charts of 4 patients undergoing bilateral hand-assisted laparoscopic nephrectomy for symptomatic autosomal dominant polycystic kidney disease between June 2000 and January 2001. Follow-up consisted of chart review and telephone survey. RESULTS: All 4 patients underwent successful bilateral hand-assisted laparoscopic nephrectomy, with a mean operative time of 286 minutes. This included 1 patient who underwent simultaneous laparoscopic marsupialization of symptomatic hepatic cysts. The average size of the polycystic kidneys removed was 1582 g. Complications included acute tubular necrosis of a renal allograft in 1 patient that resolved spontaneously and retained retroperitoneal cystic fluid that required percutaneous drainage in another patient. All patients did well postoperatively, with complete resolution of their presenting symptoms. Those with renal allografts had stable function at the last follow-up visit. CONCLUSIONS: Bilateral hand-assisted laparoscopic nephrectomy using a single HandPort incision is a feasible alternative for the removal of symptomatic polycystic kidneys. It offers the advantage of easier identification and control of hilar structures that are often obscured by the distorted renal anatomy. In addition, it allows the simultaneous performance of other intra-abdominal procedures.

Endoscopic renal papillary biopsies: a tissue retrieval technique for histological studies in patients with nephrolithiasis.

PURPOSE: The mechanisms behind calcium nephrolithiasis remain unclear. Previous research has relied on animal models or cell lines, yielding limited insight into the pathophysiology of human calcium stone disease. To determine changes occurring in the human kidney during active stone disease we used an endoscopic renal papillary biopsy protocol in calcium stone formers undergoing percutaneous nephrolithotomy. MATERIALS AND METHODS: Following stone burden clearance via percutaneous nephrolithotomy 15 idiopathic calcium oxalate and 4 ileal bypass stone formers underwent flexible and rigid nephroscopy. Biopsies from select papillae in the peripheral and interpolar regions were obtained with 5Fr flexible cup biopsy forceps. A papilla adjacent to the accessed calix was biopsied with 10Fr cup biopsy forceps. Cortical biopsies along the access tract were also obtained with the 10Fr forceps. RESULTS: All patients had successful biopsy completion. No complications were attributable to the biopsy process and no blood transfusions were required. Of the 19 patients 12 were contacted for followup at a mean of 21.7 +/- 9.0 months with none experiencing adverse sequelae such as bleeding or significant pain. A total of 14 patients had followup serum creatinine available showing that the difference in mean preoperative and postoperative values was not clinically significant (1.00 +/- 0.27 and 1.11 +/- 0.27 mg/dl, respectively). The quality of biopsied tissue permitted accurate immunohistochemical staining of crystal deposits and mineral analysis. CONCLUSIONS: Endoscopic papillary biopsies were performed safely in a small patient population. Tissue obtained using this protocol can be used for detailed histological and analytical studies, which may lead to significant advances in our understanding of stone formation mechanisms.

Urine calcium and volume predict coverage of renal papilla by Randall's plaque.

BACKGROUND: Renal papillary plaques are common in calcium stone formers. We hypothesized that plaque should increase directly with urine calcium excretion, and inversely with urine volume. To test this, we measured papillary plaque areas in both idiopathic calcium oxalate stone formers and nonstone formers and examined 24-hour urine data to identify significant correlations. METHODS: Fourteen stone formers and four nonstone forming controls underwent papillary mapping with flexible nephroscopy. For each papillum, representative still images and moving pictures expert group (MPEG) movies were used to identify plaque extent and papillary borders. The mean fractional plaque coverage for each polar region (upper, inter, lower) and per papillum was calculated. The relationship of the plaque coverage data to urine measurements was assessed with general multivariate linear modeling. RESULTS: Mean polar fractional plaque coverage was higher in the calcium oxalate stone formers (7.4% vs. 0.5%, P= 0.012) as was mean fractional plaque per papillum (7.6% vs. 0.6%, P= 0.011). When correlating mean polar plaque coverage to urine data, urine volume and calcium excretion were the only measurements with independent relationships to plaque (P= 0.002, adjusted multiple R2= 0.521), with higher calcium and lower volume increasing coverage. The same relationships hold for mean plaque per papillum, except that urine pH also becomes an independent factor (P= 0.001, adjusted multiple R2= 0.606). CONCLUSION: Utilizing advanced digital video and endoscopic equipment, we have achieved the most accurate estimation of papillary plaque coverage to date. Our findings support the idea that urine volume and calcium are the main correlates of plaque coverage.