Sean A. Pierre

Renal Stone Assessment with Dual-Energy Multidetector CT and Advanced Postprocessing Techniques: Improved Characterization of Renal Stone Composition—Pilot Study

PURPOSE To prospectively evaluate the capability of noninvasive, simultaneous dual-energy (DE) multidetector computed tomography (CT) to improve characterization of human renal calculi in an anthropomorphic DE renal phantom by introducing advanced postprocessing techniques, with ex vivo renal stone spectroscopy as the reference standard. MATERIALS AND METHODS Fifty renal calculi were assessed: Thirty stones were of pure crystalline composition (uric acid, cystine, struvite, calcium oxalate, calcium phosphate, brushite), and 20 were of polycrystalline composition. DE CT was performed with a 64-detector CT unit. A postprocessing algorithm (DECT(Slope)) was proposed as a pixel-by-pixel approach to generate Digital Imaging and Communications in Medicine dataset gray-scale-encoding ratios of relative differences in attenuation values of low- and high-energy DE CT. Graphic analysis, in which clusters of equal composition were identified, was performed by sorting attenuation values of color composition-encoded calculi in an ascending sequence. Multivariate general linear model analysis was used to determine level of significance to differentiate composition on native and postprocessed DE CT images. RESULTS Graphic analysis of native DE CT images was used to identify clusters for uric acid (453-629 HU for low-energy CT, 443-615 HU for high-energy CT), cystine (725-832 HU for low-energy CT, 513-747 HU for high-energy CT), and struvite (1337-1530 HU for low-energy CT, 1007-1100 HU for high-energy CT) stones; high-energy clusters showed attenuation value overlap. Polycrystalline calcium oxalate and calcium phosphate calculi were found throughout the entire spectrum, and dense brushite had attenuation values of more than 1500 HU for low-energy CT and more than 1100 HU for high-energy CT. The DE CT algorithm was used to generate specific identifiers for uric acid (77-80 U(Slope), one outlier), cystine (70-71 U(Slope)), struvite (56-60 U(Slope)), calcium oxalate and calcium phosphate (17-59 U(Slope)), and brushite (4-15 U(Slope)) stones. Statistical analysis showed that all compositions were identified unambiguously with the DECT(Slope) algorithm. CONCLUSION DE multidetector CT with advanced postprocessing techniques improves characterization of renal stone composition beyond that achieved with single-energy multidetector CT acquisitions with basic attenuation assessment.

Radiation Exposure in the Acute and Short-Term Management of Urolithiasis at 2 Academic Centers

PURPOSE Diagnostic imaging has a central role in the evaluation and management of urolithiasis. A variety of modalities are available, each with benefits and limitations. Without careful consideration of imaging modalities in quantity and type patients may receive excessive doses of radiation during initial diagnostic and followup evaluations. Therefore, we determined the effective radiation dose associated with an acute stone episode and short-term followup. MATERIALS AND METHODS A multicenter retrospective study of all patients who presented with an acute stone episode was performed. The analysis included all imaging studies related to stone disease performed within 1 year of the acute event. Using accepted effective radiation dose standards for each of these examinations, the total radiation dose administered was calculated and compared by patient characteristics including stone location, stone number and intervention strategy. The primary outcome assessed was a total radiation dose greater than 50 mSv, the recommended yearly dose limit for occupational exposure by the International Commission on Radiological Protection. RESULTS We identified 108 patients who presented to our respective institutions with a primary acute stone episode between 2000 and 2006. The mean age in our cohort was 48.6 years and 50% of the patients were men. Patients underwent an average of 4 radiographic examinations during the 1-year period. Studies performed included a mean of 1.2 plain abdominal films of the kidneys, ureters and bladder (range 0 to 7), 1.7 abdominopelvic computerized tomograms (range 0 to 6) and 1 excretory urogram (range 0 to 3) during the first year of followup. The median total effective radiation dose per patient was 29.7 mSv (IQR 24.2, 45.1). There were 22 (20%) patients who received greater than 50 mSv. Analysis of stone location, number of stones, stone composition, patient age, sex and surgical intervention indicated no statistically significant difference in the probability of receiving a total radiation dose greater than 50 mSv. CONCLUSIONS A fifth of patients receive potentially significant radiation doses in the short-term followup of an acute stone event. Radiographic imaging remains an integral part of the diagnosis and management of symptomatic urolithiasis. While debate exists regarding the threshold level for radiation induced fatal malignancies, urologists must be cognizant of the radiation exposure to patients, and seek alternative imaging strategies to minimize radiation dose during acute and long-term stone management.

Trainees do not negatively impact the institutional learning curve for robotic prostatectomy as characterized by operative time, estimated blood loss, and positive surgical margin rate.

OBJECTIVES We evaluated the learning curves and perioperative outcomes of an experienced laparoscopic surgeon and his trainees to assess our structured teaching program. METHODS We retrieved 383 patients undergoing robot-assisted laparoscopic prostatectomy (RALP) from our database. Trainees completed a structured teaching program and were categorized as early (days 0 to 232), mid (days 566 to 797), and late (days 825 to 1218) according to the time period in which they were working with the mentor. We compared operative times, estimated blood loss (EBL), and positive surgical margin (PSM) rates between the trainees and the mentor (Mann-Whitney and Chi-square test). Association of EBL, body mass index (BMI), and prostate weight with operative time was evaluated in multivariate linear regression analysis. RESULTS Median operative times of the early, mid, and late trainees (258, 220, and 200 minutes) significantly decreased and were similar to the corresponding senior surgeons (254, 242, and 180 minutes). Operative times decreased with lower BMI, EBL, and prostate weight (P = 0.006, P <0.001, and P <0.001, respectively). Overall, EBL (150 mL vs. 150 mL, P = 0.215) and PSM rates (20% vs. 18.6%, P = 0.741) did not differ between the mentor and the trainees. CONCLUSIONS A structured teaching program for RALP is effective and trainees are able to adopt the increased efficiency and skills of their mentor. Lower BMI, EBL, and prostate weight were associated with shorter operative times. Trainees performing the procedure did not negatively affect EBL and positive surgical margin rate.

Holmium laser for stone management.

The efficiency and safety profile of the holmium laser has made this tool a versatile multi-purpose instrument for use in the endoscopic treatment of a wide variety of urologic disorders, in particular urinary calculi. Herein we review holmium laser physics, current endourologic laser lithotripsy applications, and the performance of new low power holmium laser devices.

Impact of Long-Term Potassium Citrate Therapy on Urinary Profiles and Recurrent Stone Formation

PURPOSE Potassium citrate therapy has become one of the cornerstones of medical stone management. We elucidated the long-term effects of potassium citrate on urinary metabolic profiles and its impact on stone formation rates. MATERIALS AND METHODS We performed a retrospective cohort study in patients treated at the Comprehensive Kidney Stone Center at our institution between 2000 and 2006. Patients with pre-therapy and post-therapy 24-hour urinary profiles available who remained on potassium citrate for at least 6 months were included in the analysis. RESULTS Of the 1,480 patients with 24-hour urinary profiles 503 met study inclusion criteria. Mean therapy duration was 41 months (range 6 to 168). Overall a significant and durable change in urinary metabolic profiles was noted as soon as 6 months after the onset of therapy. These changes included increased urinary pH (5.90 to 6.46, p <0.0001) and increased urinary citrate (470 to 700 mg a day, p <0.0001). The stone formation rate also significantly decreased after the initiation of potassium citrate from 1.89 to 0.46 stones per year (p <0.0001). There was a 68% remission rate and a 93% decrease in the stone formation rate. CONCLUSIONS Potassium citrate provides a significant alkali and citraturic response during short-term and long-term therapy with the change in urinary metabolic profiles sustained as long as 14 years of treatment. Moreover, long-term potassium citrate significantly decreases the stone formation rate, confirming its usefulness in patients with recurrent nephrolithiasis.

First Prize (Tie): Dual-Energy Computed Tomography with Advanced Postimage Acquisition Data Processing: Improved Determination of Urinary Stone Composition

INTRODUCTION The characterization of urinary calculi using noninvasive methods has the potential to affect clinical management. CT remains the gold standard for diagnosis of urinary calculi, but has not reliably differentiated varying stone compositions. Dual-energy CT (DECT) has emerged as a technology to improve CT characterization of anatomic structures. This study aims to assess the ability of DECT to accurately discriminate between different types of urinary calculi in an in vitro model using novel postimage acquisition data processing techniques. METHODS Fifty urinary calculi were assessed, of which 44 had >or=60% composition of one component. DECT was performed utilizing 64-slice multidetector CT. The attenuation profiles of the lower-energy (DECT-Low) and higher-energy (DECT-High) datasets were used to investigate whether differences could be seen between different stone compositions. RESULTS Postimage acquisition processing allowed for identification of the main different chemical compositions of urinary calculi: brushite, calcium oxalate-calcium phosphate, struvite, cystine, and uric acid. Statistical analysis demonstrated that this processing identified all stone compositions without obvious graphical overlap. CONCLUSION Dual-energy multidetector CT with postprocessing techniques allows for accurate discrimination among the main different subtypes of urinary calculi in an in vitro model. The ability to better detect stone composition may have implications in determining the optimum clinical treatment modality for urinary calculi from noninvasive, preprocedure radiological assessment.

Use of the Escape™ Nitinol Stone Retrieval Basket Facilitates Fragmentation and Extraction of Ureteral and Renal Calculi: A Pilot Study

BACKGROUND AND PURPOSE Advances in ureteroscope and stone basket design have catapulted ureteroscopy to the forefront of surgical stone management; however, persistent problems such as stone migration continue to challenge urologists. The Escape nitinol stone retrieval basket (Boston Scientific, Natick, MA) is a stone basket designed to capture calculi and facilitate simultaneous laser lithotripsy in situ. We report our initial experience with the Escape basket for the management of urinary calculi and compare the use of this device with other methods of optimizing ureteroscopic stone management. PATIENTS AND METHODS A prospective evaluation of 23 patients undergoing ureteroscopic holmium:yttrium-aluminum-garnet laser lithotripsy of urinary calculi was performed at two institutions by two surgeons (R.M. and G.M.P). The Escape basket was used to prevent retrograde ureteral stone migration or to facilitate fragmentation and extraction of large renal calculi. Patient demographics and perioperative parameters were assessed. RESULTS Twenty-three patients (16 men, 7 women), with a mean age of 55.5 years (range 33-74 yrs) were treated for renal (n = 9) or ureteral (n = 14) calculi. The mean stone diameter was 1.4 cm (range 0.4-2.5 cm), mean fragmentation time was 44.1 minutes (range 10-75 min), and mean energy used was 3.1 kJ (range 0.4-10.6 kJ). No complications were encountered. Eighty-seven percent (20/23) of patients were rendered completely stone free after ureteroscopic laser lithotripsy using the Escape basket. Of the three patients with residual calculi, one patient with a 2.5-cm renal calculus had residual fragments larger than 3 mm, and two patients with large renal calculi had residual fragments smaller than 3 mm. CONCLUSIONS The Escape basket appears to be safe and effective in preventing stone migration and facilitating ureteroscopic laser lithotripsy and stone extraction.

High Definition Laparoscopy: Objective Assessment of Performance Characteristics and Comparison with Standard Laparoscopy

INTRODUCTION High definition (HD) digital imaging represents a major advance in endoscope technology. The development of the charge-coupled device chip and its location at the distal end of the endoscope allows for image capture and digitization, as well as specific light filtration and processing. We assessed the capability of HD technology combined with digital imaging to provide improved image quality and enhanced spatial three-dimensional positioning. METHODS A HD digital laparoscope and a standard definition (SD) laparoscope were evaluated in the laboratory setting to assess and compare image resolution, brightness, contrast, and color reproducibility, using standard industry testing protocols. RESULTS Compared with the SD laparoscope, the HD laparoscope had superior resolution at 50 mm distance (2.4 line pairs/mm v 2.0 line pairs/mm), increased image brightness (129 lumens v 112 lumens), increased depth of field, and decreased distortion. Color and grayscale reproduction were found to be similar for the two laparoscopes. CONCLUSION HD laparoscopy has superior objective performance characteristics compared with standard laparoscopes. Further investigation is required to determine whether these objective findings translate into subjective improvements, and which characteristics can be adjusted to obtain the best possible results. These improved optics may lead to easier identification of anatomic structures, finer dissection, and enhanced three-dimensional spatial positioning during HD laparoscopic procedures.

TUBELESS-STENTLESS PERCUTANEOUS NEPHROLITHOTOMY: A FURTHER ADVANCE IN PERCUTANEOUS URINARY STONE MANAGEMENT

INTRODUCTION AND OBJECTIVES: Multiple authors have recently reported their experience with tubeless percutaneous nephrolithotomy (PNL) demonstrating its safety and efficacy. Postoperatively, tubeless PNL patients have an indwelling ureteral stent placed, often associated with stent-related morbidity. The concept of the tubeless-“stentless” PNL, where an open-ended ureteral catheter is removed prior to hospital discharge, is an emerging technique to further reduce PNL-related morbidity. We review our initial experience with tubeless-stentless PNL. METHODS: An IRB approved retrospective review of our nephrolithiasis database was performed to identify all patients who underwent tubeless-stentless PNL. Patients underwent PNL by a single surgeon and had an open-ended ureteral catheter placed at the start of the case, which was removed prior to discharge from the hospital. No nephrostomy tube or ureteral stent was left post-procedure. We reviewed patient age, ASA, anatomic anomalies, BMI, stone burden, number and location of access tracts, length of stay (LOS), change in hemoglobin, transfusion rate, and peri-operative complications. RESULTS: Between 7/07 and 10/08 49 patients underwent tubeless-stentless PNL. Mean age was 50.4yrs (range 22-81), and mean stone burden was 513.91 mm2 (range 99.1-2037.3). Three patients (6%) had horseshoe kidneys. The cohort’s mean ASA and BMI were 2.5 and 31.6 (range 14.2-61.4), respectively. The mean change in hemoglobin was 2.08 g/dL (range 0.5-4.7). Two patients (4%) required a blood transfusion. Mean LOS was 1.8 days and 35 patients (71.4%) were discharged within 24 hours of surgery. Seven patients (14%) had 2 nephrostomy tracts. Seven patients (14%) had supracostal access tracts. The complications that occurred in patients with 2 nephrostomy tracts included 1 pleural effusion, 1 pulmonary embolus, and 1 hemothorax/ pneumothorax. Among those patients with 1 nephrostomy tract, 1 patient had a perinephric urinoma. The complication rate among those with multiple tracts was 43% versus 2% in those patients with a single tract. No patients had significant voiding symptoms following their discharge. CONCLUSIONS: Tubeless-stentless PNL appears to be a safe alternative for patients who require percutaneous stone removal. Further investigations are required, to determine its effectiveness and optimize patient selection criteria, compared to traditional PNL techniques.

Evaluation of a new multi-basket load-release ureteral stent.

INTRODUCTION A multi-basket ureteral stent was tested and modified to assess feasibility of load-release features intended to release stone(s) if resistance is encountered during stent removal. METHODS Three versions of the stent were evaluated: (1) unaltered stent, (2) one strand of each basket partially cut to 50%, or 75% (3) tube between baskets longitudinally slit. One of the baskets was filled with multiple 3-4-mm stones or a single large 6-mm stone to 20Fr diameter. The force required to release the device through a tube with an 8Fr narrowing was determined. In a separate assessment, urologists used a string attached to the force gauge to exert the maximum force they would be comfortable using in ureteral stent removal. RESULTS The unaltered stent was associated with higher release forces or inability to remove the stent: 18.67 +/- 8.35 N when a single large stone was present, compared to 8.46 +/- 2.75 N for multiple small stones. Modified devices with 50% and 75% cut basket strands released at 15.19 +/- 1.54 N, and 10.65 +/- 2.09 N, respectively. The longitudinal slit device released at 3.11 +/- 1.57 N. The maximum force exerted by urologists in simulated stent removal was 7.3 +/- 0.4 N. CONCLUSION Modifications to the multi-basket ureteral stent allow for stent removal in an in vitro model with a narrowing present with stone(s) in the stent baskets. The longitudinal slit modification appears to allow for stent removal with forces low enough to prevent significant ureteral injury, even if ureteral strictures are present.