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International Journal of Urology (2015) 22, 372–377
doi: 10.1111/iju.12690
Original Article: Clinical Investigation
Preoperative factors predicting spontaneous clearance of residual stone fragments after flexible ureteroscopy Hiroki Ito,1,2 Shinnosuke Kuroda,1 Takashi Kawahara,2 Kazuhide Makiyama,2 Masahiro Yao2 and Junichi Matsuzaki1 1
Department of Urology, Ohguchi East General Hospital, and 2Department of Urology, Yokohama City University Graduate School of Medicine, Yokohama, Kanagawa, Japan Abbreviations & Acronyms AUROC = area under the receiver operating characteristics BMI = body mass index fURS = lithotripsy with flexible ureteroscopy KUB = kidney–ureter– bladder NCCT = non-contrast computed tomography PCNL = percutaneous nephrolithiaisis POD = postoperative day POM = postoperative month RF = residual fragment SCRF = the spontaneous clearance of residual renal fragments SF = stone free SWL = shock-wave lithotripsy URS = ureteroscopy
Correspondence: Hiroki Ito M.D., Department of Urology, Yokohama City University Graduate School of Medicine, 3-9 Fukuura, Kanazawa-ku, Yokohama City, Kanagawa 2360012, Japan. Email: [email protected] Received 22 July 2014; accepted 9 November 2014. Online publication 19 January 2015
372
Objective: To investigate factors predicting spontaneous clearance of residual renal fragments after flexible ureteroscopy. Methods: Among 546 patients who underwent lithotripsy with flexible ureteroscopy, 81 had residual renal fragments, as determined by kidney–ureter–bladder films on postoperative day 1. The final outcome was determined at 3 months after the last flexible ureteroscopy session using non-contrast computed tomography. Patient characteristics and preoperative factors were analyzed using the unpaired t-test and 2-test. Correlations between the possible predictive factors and the spontaneous clearance of residual renal fragments after flexible ureteroscopy were analyzed using a multivariate logistic regression model with backward selection. Results: Non-contrast computed tomography at postoperative month 3 showed that 33 cases (40.7%) had spontaneous clearance of residual renal fragments, whereas 48 (59.3%) showed non-clearance. Significant differences were found between these cases in terms of stone number, stone location, presence of lower pole calculi and preoperative stent placement. Multivariate assessment showed that stone number (P = 0.004), presence of lower pole calculi (P = 0.021) and presence of hydronephrosis (P = 0.024) were independent predictors of the spontaneous clearance of residual renal fragments after flexible ureteroscopy. Conclusions: Stone number, presence of lower pole calculi and presence of hydronephrosis are independent predictive factors of the spontaneous clearance of residual renal fragments after flexible ureteroscopy.
Key words:
computed tomography, helical, kidney stone, lithotripsy, multivariate analysis, ureteroscopy.
Introduction Achieving a SF status is important for preventing postoperative events related to residual stone fragments after endourological procedures, and considerable attention is now being paid to identifying what constitutes clinically insignificant residual renal fragments after these procedures.1–7 Some studies have evaluated the natural history of residual fragments after SWL and PCNL.1,2 These studies showed that some patients with residual fragments who experience a symptomatic episode require additional intervention within 2–3 years of SWL or PCNL.1,2 In contrast, the natural history of residual stone fragments after URS has not been examined extensively. In their study of 46 patients with post-URS renal stone fragments ≤4 mm, Rebuck et al. suggested that approximately one in five (or 19.6%) patients experience a stone-related event in the 1.6 years after URS.4 The remaining patients either become stone free through spontaneous passage or retain asymptomatic fragments of stable size.4 However, studies with a larger patient population are required to determine the rate of SCRF after URS. Recently, with the development of the ureteroscope and assistant technical devices, lithotripsy with fURS has become the standard treatment option for urinary stones, similar to SWL or PCNL.8–12 Accurate pre-fURS prediction of the rate of SCRF would definitely help surgeons determine the possible outcomes of fURS, and thereby select optimal treatment options preoperatively. However, to our knowledge, no studies have been carried out to identify factors that predict SCRF after endourological surgeries, including fURS. © 2015 The Japanese Urological Association
Predicting clearance of residual stone fragments
To this end, the present study determined both the rate of SCRF after fURS and the factors that predict SCRF after fURS. To our knowledge, this is the first study to identify the preoperative predictors of SCRF after fURS.
Methods We retrospectively reviewed the cases of 546 patients treated with fURS with or without semi-rigid URS procedures for urinary stones between December 2009 and December 2012 at Ohguchi East General Hospital, Japan. Second- and thirdstage URS was carried out in five and one patients, respectively. The primary options for the treatment of urinary stones were SWL for patients with urinary stones 20 mm diameter. For all patients, URS was offered as the first or second option. The final choice of treatment modality depended on the patients’ decision and the surgeon’s preference.13–15 The present study was approved by the ethics committee of Ohguchi East General Hospital. Written informed consent was obtained from all patients for their data to be used for research purposes.
Surgical techniques The surgical procedures used are described elsewhere.16 Briefly, URS was carried out with a 6/7.5-Fr or 8/9.8-Fr semirigid ureteroscope (Richard-Wolf, Knittlingen, Germany), a 6-Fr flexible ureteroscope (Flex-X2; STORZ, Tuttlingen, Germany or Olympus P-5; Olympus, Tokyo, Japan), or both, with a 200–550 μm holmium:yttrium-aluminum-garnet laser. During all procedures, ureteral access sheaths (12/14-Fr or 14/16-Fr from Cook Medical, Bloomington, IN, USA or 11/13 or 13/15-Fr from Boston Scientific, Natick, MA, USA) were used to facilitate stone extraction and reduce the intrarenal pressure. For stone removal and clearance of residual fragments, 1.5-Fr or 2.2-Fr tipless nitinol baskets were used in all procedures. Before fragmentation, lower pole stones were relocated using these baskets. If the operation time exceeded 120 min, the procedure was stopped to minimize perioperative complications.
Pre- and postoperative evaluation Stone status was routinely evaluated on KUB films on POD 1. SF status was defined as no visible stones; when residual stone fragments ≤4 mm were detected, the outcome was recorded as RF status. The final outcome of fURS was decided on NCCT carried out 3 months after the last fURS session. The preoperative factors analyzed were stone diameter (mm), stone volume (mm3), stone number, stone side (right or left), age, sex, height, bodyweight, BMI, presence of hydronephrosis (including partial hydronephrosis), presence of lower pole calculi, preoperative placement of ureteral stent and stone location (ureter stones, renal stones, or both). Stone volume was determined on 5 mm axial and 3.5 mm reconstructed coronal NCCT images, as described previously.13 The number of stones, © 2015 The Japanese Urological Association
presence of hydronephrosis and lower pole calculi, and stone location were evaluated on preoperative NCCT images and before the fURS procedures. For all procedures, stone status was decided by the same urologist (HI).
Statistical analysis Statistical analysis was carried out using Statistical Package for Social Sciences, version 21 (SPSS, Chicago, IL, USA). Patient characteristics and preoperative factors were analyzed using the unpaired t-test and 2-test. The AUROC was used to evaluate the predictive potential of age, BMI, stone burden and stone number. The cut-off points used for categorizing stone number were set depending on the highest value of both sensitivity and specificity determined from the ROC curve. The cut-off points of stone volume and Hounsfield units were set at 1000 mm3 and 1500 HU, respectively. The operators were eight urologists. A multivariate logistic regression model with backward selection was also used for statistical analysis.15,17,18 All variables that showed significant correlation in the full multivariate model (P < 0.15) were included in the reduced multivariate model. In all statistical tests, P < 0.05 was considered significant.
Results Patient characteristics and surgical outcomes Among a total of 546 URS procedures carried out, 342 were found to be have SF status as the outcome, 123 were considered failures and 81 had RF status (fragments ≤4 mm) on POD 1. The 81 patients with RF status were subsequently further analyzed. NCCT in POM 3 showed that of these 81 cases, 33 cases (40.7%) showed SCRF and 48 (59.3%) showed non-SCRF. In all 81 cases, the procedures were carried out under general anesthesia. Flexible URS with lithotripsy alone was carried out in 54 procedures, whereas the other 27 procedures involved both semirigid and flexible URS with lithotripsy. Postoperative ureteral stent placement was carried out in all procedures to reduce the risk of complications; the stents were removed at approximately POM 1, when we were certain that the bypass was no longer necessary. Medical expulsive treatment, including an alpha 1 blocker, was not administered up to POM 3 in any of the cases. Table 1 shows a comparison of patient characteristics and treatment outcomes according to SCRF observed in POM 3. Significant differences were found between the SCRF and non-SCRF groups in stone number (P = 0.019), stone location (P = 0.042), presence of lower pole calculi (P = 0.025) and preoperative stent placement (P = 0.010). In terms of postoperative complications, high-grade fever occurred in four patients, and they received conservative treatment (Clavien classification, grade II). Ureteral stricture developed in two patients, neither of whom had any obvious perioperative problems. Balloon dilation of the ureter was carried out in both cases, and a successful outcome was obtained in one patient (Clavien classification, grade III). In the second patient, as the balloon dilation failed, permanent double-J stents were placed (Clavien classification, grade III). 373
H ITO ET AL.
Table 1 Comparison of patient outcomes in POM 3 and stone data between the SCRF group and non-SCRF group
No. patients Age (years) Sex (n) Side (n) Height (cm) Bodyweight (kg) 2 BMI (cm/kg ) Stage
Semi-rigid URS (n) No. stones Stone burden Stone location
Lower pole calculi Hounsfield unit Hydronephrosis (n) Preoperative stenting
SWL failure (n) Operation time (min) Laser use (kJ) Operator Postoperative admission days Postoperative fever (n) Postoperative ureteral stricture (n) Stone composition
Female Male Right Left
1 2 3 Without With Diameter (mm) 3 Volume (mm ) Ureter Kidney Ureter + kidney Absent Present Maximum Mean Cases Indwelling duration (months) Size 5-Fr 6-Fr 7-Fr 8-Fr
50 URS performed
International Journal of Urology (2015) 22, 372–377
doi: 10.1111/iju.12690
Original Article: Clinical Investigation
Preoperative factors predicting spontaneous clearance of residual stone fragments after flexible ureteroscopy Hiroki Ito,1,2 Shinnosuke Kuroda,1 Takashi Kawahara,2 Kazuhide Makiyama,2 Masahiro Yao2 and Junichi Matsuzaki1 1
Department of Urology, Ohguchi East General Hospital, and 2Department of Urology, Yokohama City University Graduate School of Medicine, Yokohama, Kanagawa, Japan Abbreviations & Acronyms AUROC = area under the receiver operating characteristics BMI = body mass index fURS = lithotripsy with flexible ureteroscopy KUB = kidney–ureter– bladder NCCT = non-contrast computed tomography PCNL = percutaneous nephrolithiaisis POD = postoperative day POM = postoperative month RF = residual fragment SCRF = the spontaneous clearance of residual renal fragments SF = stone free SWL = shock-wave lithotripsy URS = ureteroscopy
Correspondence: Hiroki Ito M.D., Department of Urology, Yokohama City University Graduate School of Medicine, 3-9 Fukuura, Kanazawa-ku, Yokohama City, Kanagawa 2360012, Japan. Email: [email protected] Received 22 July 2014; accepted 9 November 2014. Online publication 19 January 2015
372
Objective: To investigate factors predicting spontaneous clearance of residual renal fragments after flexible ureteroscopy. Methods: Among 546 patients who underwent lithotripsy with flexible ureteroscopy, 81 had residual renal fragments, as determined by kidney–ureter–bladder films on postoperative day 1. The final outcome was determined at 3 months after the last flexible ureteroscopy session using non-contrast computed tomography. Patient characteristics and preoperative factors were analyzed using the unpaired t-test and 2-test. Correlations between the possible predictive factors and the spontaneous clearance of residual renal fragments after flexible ureteroscopy were analyzed using a multivariate logistic regression model with backward selection. Results: Non-contrast computed tomography at postoperative month 3 showed that 33 cases (40.7%) had spontaneous clearance of residual renal fragments, whereas 48 (59.3%) showed non-clearance. Significant differences were found between these cases in terms of stone number, stone location, presence of lower pole calculi and preoperative stent placement. Multivariate assessment showed that stone number (P = 0.004), presence of lower pole calculi (P = 0.021) and presence of hydronephrosis (P = 0.024) were independent predictors of the spontaneous clearance of residual renal fragments after flexible ureteroscopy. Conclusions: Stone number, presence of lower pole calculi and presence of hydronephrosis are independent predictive factors of the spontaneous clearance of residual renal fragments after flexible ureteroscopy.
Key words:
computed tomography, helical, kidney stone, lithotripsy, multivariate analysis, ureteroscopy.
Introduction Achieving a SF status is important for preventing postoperative events related to residual stone fragments after endourological procedures, and considerable attention is now being paid to identifying what constitutes clinically insignificant residual renal fragments after these procedures.1–7 Some studies have evaluated the natural history of residual fragments after SWL and PCNL.1,2 These studies showed that some patients with residual fragments who experience a symptomatic episode require additional intervention within 2–3 years of SWL or PCNL.1,2 In contrast, the natural history of residual stone fragments after URS has not been examined extensively. In their study of 46 patients with post-URS renal stone fragments ≤4 mm, Rebuck et al. suggested that approximately one in five (or 19.6%) patients experience a stone-related event in the 1.6 years after URS.4 The remaining patients either become stone free through spontaneous passage or retain asymptomatic fragments of stable size.4 However, studies with a larger patient population are required to determine the rate of SCRF after URS. Recently, with the development of the ureteroscope and assistant technical devices, lithotripsy with fURS has become the standard treatment option for urinary stones, similar to SWL or PCNL.8–12 Accurate pre-fURS prediction of the rate of SCRF would definitely help surgeons determine the possible outcomes of fURS, and thereby select optimal treatment options preoperatively. However, to our knowledge, no studies have been carried out to identify factors that predict SCRF after endourological surgeries, including fURS. © 2015 The Japanese Urological Association
Predicting clearance of residual stone fragments
To this end, the present study determined both the rate of SCRF after fURS and the factors that predict SCRF after fURS. To our knowledge, this is the first study to identify the preoperative predictors of SCRF after fURS.
Methods We retrospectively reviewed the cases of 546 patients treated with fURS with or without semi-rigid URS procedures for urinary stones between December 2009 and December 2012 at Ohguchi East General Hospital, Japan. Second- and thirdstage URS was carried out in five and one patients, respectively. The primary options for the treatment of urinary stones were SWL for patients with urinary stones 20 mm diameter. For all patients, URS was offered as the first or second option. The final choice of treatment modality depended on the patients’ decision and the surgeon’s preference.13–15 The present study was approved by the ethics committee of Ohguchi East General Hospital. Written informed consent was obtained from all patients for their data to be used for research purposes.
Surgical techniques The surgical procedures used are described elsewhere.16 Briefly, URS was carried out with a 6/7.5-Fr or 8/9.8-Fr semirigid ureteroscope (Richard-Wolf, Knittlingen, Germany), a 6-Fr flexible ureteroscope (Flex-X2; STORZ, Tuttlingen, Germany or Olympus P-5; Olympus, Tokyo, Japan), or both, with a 200–550 μm holmium:yttrium-aluminum-garnet laser. During all procedures, ureteral access sheaths (12/14-Fr or 14/16-Fr from Cook Medical, Bloomington, IN, USA or 11/13 or 13/15-Fr from Boston Scientific, Natick, MA, USA) were used to facilitate stone extraction and reduce the intrarenal pressure. For stone removal and clearance of residual fragments, 1.5-Fr or 2.2-Fr tipless nitinol baskets were used in all procedures. Before fragmentation, lower pole stones were relocated using these baskets. If the operation time exceeded 120 min, the procedure was stopped to minimize perioperative complications.
Pre- and postoperative evaluation Stone status was routinely evaluated on KUB films on POD 1. SF status was defined as no visible stones; when residual stone fragments ≤4 mm were detected, the outcome was recorded as RF status. The final outcome of fURS was decided on NCCT carried out 3 months after the last fURS session. The preoperative factors analyzed were stone diameter (mm), stone volume (mm3), stone number, stone side (right or left), age, sex, height, bodyweight, BMI, presence of hydronephrosis (including partial hydronephrosis), presence of lower pole calculi, preoperative placement of ureteral stent and stone location (ureter stones, renal stones, or both). Stone volume was determined on 5 mm axial and 3.5 mm reconstructed coronal NCCT images, as described previously.13 The number of stones, © 2015 The Japanese Urological Association
presence of hydronephrosis and lower pole calculi, and stone location were evaluated on preoperative NCCT images and before the fURS procedures. For all procedures, stone status was decided by the same urologist (HI).
Statistical analysis Statistical analysis was carried out using Statistical Package for Social Sciences, version 21 (SPSS, Chicago, IL, USA). Patient characteristics and preoperative factors were analyzed using the unpaired t-test and 2-test. The AUROC was used to evaluate the predictive potential of age, BMI, stone burden and stone number. The cut-off points used for categorizing stone number were set depending on the highest value of both sensitivity and specificity determined from the ROC curve. The cut-off points of stone volume and Hounsfield units were set at 1000 mm3 and 1500 HU, respectively. The operators were eight urologists. A multivariate logistic regression model with backward selection was also used for statistical analysis.15,17,18 All variables that showed significant correlation in the full multivariate model (P < 0.15) were included in the reduced multivariate model. In all statistical tests, P < 0.05 was considered significant.
Results Patient characteristics and surgical outcomes Among a total of 546 URS procedures carried out, 342 were found to be have SF status as the outcome, 123 were considered failures and 81 had RF status (fragments ≤4 mm) on POD 1. The 81 patients with RF status were subsequently further analyzed. NCCT in POM 3 showed that of these 81 cases, 33 cases (40.7%) showed SCRF and 48 (59.3%) showed non-SCRF. In all 81 cases, the procedures were carried out under general anesthesia. Flexible URS with lithotripsy alone was carried out in 54 procedures, whereas the other 27 procedures involved both semirigid and flexible URS with lithotripsy. Postoperative ureteral stent placement was carried out in all procedures to reduce the risk of complications; the stents were removed at approximately POM 1, when we were certain that the bypass was no longer necessary. Medical expulsive treatment, including an alpha 1 blocker, was not administered up to POM 3 in any of the cases. Table 1 shows a comparison of patient characteristics and treatment outcomes according to SCRF observed in POM 3. Significant differences were found between the SCRF and non-SCRF groups in stone number (P = 0.019), stone location (P = 0.042), presence of lower pole calculi (P = 0.025) and preoperative stent placement (P = 0.010). In terms of postoperative complications, high-grade fever occurred in four patients, and they received conservative treatment (Clavien classification, grade II). Ureteral stricture developed in two patients, neither of whom had any obvious perioperative problems. Balloon dilation of the ureter was carried out in both cases, and a successful outcome was obtained in one patient (Clavien classification, grade III). In the second patient, as the balloon dilation failed, permanent double-J stents were placed (Clavien classification, grade III). 373
H ITO ET AL.
Table 1 Comparison of patient outcomes in POM 3 and stone data between the SCRF group and non-SCRF group
No. patients Age (years) Sex (n) Side (n) Height (cm) Bodyweight (kg) 2 BMI (cm/kg ) Stage
Semi-rigid URS (n) No. stones Stone burden Stone location
Lower pole calculi Hounsfield unit Hydronephrosis (n) Preoperative stenting
SWL failure (n) Operation time (min) Laser use (kJ) Operator Postoperative admission days Postoperative fever (n) Postoperative ureteral stricture (n) Stone composition
Female Male Right Left
1 2 3 Without With Diameter (mm) 3 Volume (mm ) Ureter Kidney Ureter + kidney Absent Present Maximum Mean Cases Indwelling duration (months) Size 5-Fr 6-Fr 7-Fr 8-Fr
50 URS performed
