| Background and ObjectionUrinary calculi is a kind of diseases that influence all geographical, cultural and ethnic groups, which has the highest percentage of hospitalized patients in urology department. According to epidemiological data, the annual incidence rate of urinary calculi in western countrieswas about 100-400/hundred thousand. In China, the incidence of urinary calculi was 1%-5%, most in the south (5% 10%); Annual incidence of 150 -200/hundred thousand, and the incidence of a disease has a tendency to increase.Kidney stones in the vast proportion of urinary calculi (about 86%), which also known as a renal calculus or nephrolith, is solid pieces of material which is formed in the kidneys from minerals in urine. Small Kidney stones typically leave the body in the urine stream, which may pass without causing symptoms. If stones grow to sufficient size (usually 3 millimeters or more), they can cause blockage of the ureter, which leads to pain, most commonly beginning in the flank or lower back and radiating to the groin. This pain is often known as renal colic. Other associated symptoms include:nausea, vomiting, fever, blood in the urine, pus in the urine, and painful urination. Blockage of the ureter can cause decreased kidney function and dilation of the kidney, severe cases can be life-threatening. So large kidney stones (usually more than 0.6 cm) usually require surgical treatment.Since the mid-1980s, minimally invasive surgical such as extracorporeal extracorporeal shock wave lithotripsy (ESWL), ureteroscopic lithotomy and Percutaneous nephrolithotomy (PCNL) were gradually replace laparotomy for urolithiasis treatment. In recent years, the flexible ureteroscope also became an option for the treatment of kidney stones, which obtain better early incomes compared with other surgical procedures. Percutaneous nephrolithotomy, however, is still the irreplaceable surgery for large kidney stones, especially staghorn calculi.Since the 1970s, percutaneous nephrolithotomy (PCNL) become anwidely accepted effective minimally invasive surgery in the treatment of large volume, complexity and staghorn kidney stones. But there is still a certain "residual stone rate" after PCNL. Urological surgeons have been looking for a prediction model of postoperative results, is to:1. In current condition, can choose patients more accurately and more chances to remove stones, at the same time reduce the incidence of complications; 2. Evaluate the various operation type objectively, optimize the operation choose, at the same time increase the calculi clearance rate; 3. Any surgeon may use it to predict his SFR, and compare to standard SFR; 4. To evaluate the operation complexity, improve the system of operation level and referral system; 5. Promote the academic exchanges, increase related literature.In 2010, Thomas, etc. reported a scoring system-Guy ’sstone score. The classification system is based on opinions of urology experts, literature review. Kidney stones can be divided into four grades, and used to predict SFR after PCNL, postoperative complications and perioperative state.In 2013, Okhunov etc. put forward a possibly better prediction model scoring system-S.T.O.N.E. nephrolithometry scoring system. It is designed to improve the condition assessment, predict stone free rate after PCNL, predict perioperative status and standardize academic reports. S.T.O.N.E. nephrolithometry scoring system based on kidney stone features acquire from computed tomography (CT) scan, including stone size (S), tract length (T), the degree of obstruction (O), The number of calices containing stones (N) and stone essence (E). Quantitative evaluation of each index, according to the score to comprehensively assess the complexity of kidney stones. But the clinical application of the scoring system in China is not much and data quantity is small. There is also no operational details for S.T.O.N.E. nephrolithometry scoring system. Some aspects of its operating instructions need improvement.In this paper, we retrospectively examined patients who underwent PCNL. Preoperative abdominopelvic computerized tomography images of these patients were reviewed. Details to adjust to the operation of the S.T.O.N.E. nephrolithometry scoring system and scored according to the Guy’s and S.T.O.N.E. scoring system. The relationship between the Guy’s stone score and S.T.O.N.E. nephrolithometry scoring system, and their postoperative stone-free status, complications based on Clavien system, perioperative status was compared.Materials and Methods1. Patients selected and information collectionThe initial 222 patients undergoing PCNL were included in the present study. These cases were performed from July 2013 to March 2015.We included only patients aged>18 years. The patients were excluded if they did not have a noncontrast-enhanced CT scan of the abdomen/pelvis before PCNL. The patients with a nephrostomy tube or ureteral stent in place at surgery were excluded, as were the patients who had undergone any open, endoscopic, or laparoscopic procedure in the same setting as the intended PCNL. Second-stage PCNL procedures were not included in the present analysis.The demographic, clinical, and operative data were collected in a prospective fashion. The information collected included age, sex, BMI, medical and surgical history, previous surgical procedures, presence of renal anomalies, American Society of Anesthesiologists score, estimated blood loss (EBL), operative time, target stone location and size, intraoperative complications, and length of stay. Postoperative complications within 30 days, were graded using the modified Clavien classification system.The primary outcome measure was the score correlation with the stone-free rate (SFR). The stone-free status was assessed for all patients using kidney-ureter-bladder (KUB) radiography. The secondary outcome measures included score correlation with the operative time, EBL, length of hospital stay, and perioperative complications. 2. Guy’s stone scoreGrade I:A solitary stone in the mid/lower pole with simple anatomy or a solitary stone in the pelvis with simple anatomy; Grade II:A solitary stone in the upper pole with simple anatomy or multiple stone in a patient with simple anatomy or any solitary stone in a patient with abnormal anatomy; Grade III:multiple stone in a patient with abnormal anatomy or stones in a calyceal diverticulum or partial staghorn calculus; Grade Ⅳ:Staghorn calculus or any stone in a patient with spina bifida or spinal injury.3. Modified S.T.O.N.E. NephrolithometryFive variables include the stone size (S), tract length (T), degree of obstruction (O), number of involved calices (N), and stone essence (E).The stone size (S) was estimated by formula [S=(lenth*sidth*height2]. The stone size was scored from 1 to 4 according to a calculated area of 0-399, 400-799,800-1599, and>1600 mm2, respectively.The tract length (T) evaluates the skin-to-stone distance. The skin-to-stone distance is defined as the mean vertical distance from the farthest edge of the stone to the skin measured on a supine noncontrast-enhanced CT film at 0°,45°, and 90°. The tract length was scored according to a mean length of≥100 mm.The obstruction (O) evaluates the degree of hydronephrosis and is scored according to the severity of dilation of the collecting system. No obstruction or mild dilation is assigned 1 point and moderate to severe dilation are assigned 2 points.The number of calices (N) containing stones. If zero or one calix is involved, a score of 1 is assigned. If 2 or 3 calices are affected, a score of 2 is assigned. A maximum score of 3 is assigned if a full staghorn calculus is present.The stone essence (E) evaluates the stone density. This is measured on preoperative CT imaging and is assigned a score according to a radiodensity threshold of>950 or<950 Hounsfield units.The scores from each variable are summed to determine the S.T.O.N.E. nephrolithometry score. The score can vary from a minimum of 5 to a maximum of 13.4. Statistical AnalysisThe Statistical Package of Social Sciences for Windows (SPSS, Chicago, IL) version 21 was used for statistical analysis.The baseline differences in patient characteristics (age, sex, BMI, American Society of Anesthesiologists score), stone features (laterality, stone size, tract length, location, presence of obstruction, number of involved calices, and essence), and perioperative data (operative duration, estimated blood loss, and length of stay) between the stone-free and nonstone-free patients were analyzed using the t test for continuous variables and the chi-square test for categorical covariates. The association of each score component with stone-free status was evaluated using the chi-square or Fischer exact test, when appropriate. The analysis of the final score with stone-free status and complications was done using logistic regression. The association of the final score with the EBL, operative duration, and length of stay was tested using linear regression analysis.Receiver operating characteristic (ROC) curves were drawn to assess the accuracies of both scoring systems for pre-operative prediction of stone-free status. The areas under the curves were compared using the online calculator of significance of difference between areas under two independent ROC curves from the following Web site http://vassarstats.net/roc_comp.html. P< 0.05 was considered statistically significant.Results1. Guy’s stone scoreFor validation, we used a series of 222 consecutive PCNL procedures performed in Nanfang Hospital. The distribution of cases according to the stone score was 23% classified as grade 1,24.3% as grade II,25.7% as grade III, and 27% as grade IV. The SFR was 69.8% of the completed procedures (range 88.2% for grade I to 46.7% for grade IV). Complications were recorded prospectively. The overall complication rate was 25.6%.Multivariate linear regression analysis (SPSS) was used to investigate factors potentially affecting SFR, Clavien complication grade, operation time, and radiation time and exposure. The stone score was the only factor that significantly and independently predicted the SFR (P=0.000). None of the other factors (ie, age, gender, laterality, BMI, operative time) correlated statistically significantly with the SFR. None of the factors correlated with the overall complication rate or severity.2. S.T.O.N.E. NephrolithometryFrom November 2013 to October 2015,293 patients underwent PCNL. Of these, 222 subjects met the inclusion criteria and were included in the present study. The patient demographics and stone characteristics were compared between the stone-free patients and those with residual stones. The overall SFR in our cohort was 69.8%. The stone-free patients and those with residual stones had a similar distribution in age, sex, stone laterality, ASA score, and BMI. The mean stone size in stone-free patients and patients with residual stones was 632 and 1183 mm2, respectively (P=0.000). The number of involved calices differed between the 2 groups(1.6±1.2 vs 2.6± 1.5; P=0.000). The stone essence was not significantly different between the 2 groups (1122± 260 vs 1153±216 Hounsfield units; P=0.388).Among the potential variables, an increasing stone size (P<.0007) and severity of hydronephrosis (P<.0006), and an increasing number of calices (P<.0019) were associated with residual stones. The skin-to-stone distance and stone density were not associated with the presence of residual stones. The S.T.O.N.E. nephrolithometry score was significantly associated with the presence of residual stones (P= 0.000). The patients with residual stones had significantly greater scores than the stone-free patients (9.45 vs 7.74, P=0.000).Overall, the S.T.O.N.E. nephrolithometry score predicting the stone-free status accurately. The S.T.O.N.E. nephrolithometry score demonstrated a correlation with the SFR, with a greater score (representing a greater degree of complexity) resulting in a lower SFR. Overall,56 patients occur postoperative complications. The postoperative events included 13 Clavien grade 2 (bleeding requiring blood transfusion in 7, postoperative fever managed with antibiotics in 24, and arrhythmia managed with antiarrhythmic medications in 2) and 3 grade 3B complications. In the multivariate logistic model, a trend was seen toward significance with the stone size (P=0.065) and number of calices (P=0.084). S.T.O.N.E. nephrolithometry not correlated with the operative time EBL and length of hospital stay.3. ComparisonWhen compared to patients with residual fragments, stone-free patients had significantly lower Guy’s grade (3.16 vs.2.31; P< 0.001) and S.T.O.N.E. score (9.45 vs.7.74; P< 0.004). However, there were no significant associations between both scoring systems and postoperative complications, EBL, operative time and LOS. Logistic regression analysis showed that both Guy’s and S.T.O.N.E. scoring systems were significantly associated with stone-free status (OR 2.197, [95% CI 1.607-3.003]; P< 0.001) and (OR 2.194, [95% CI 1.725-2.789]; P=0.001), respectively. Similarly, they were no significantly associated with the EBL, operative time and LOS.There was no significant difference in the areas under the curves for the Guy’s and S.T.O.N.E. scoring systems (GSS:0.74 [95% CI 0.66-0.82]; S.T.O.N.E. score: 0.63 [95% CI 0.54-0.72]; P=0.06)ConclusionsThe Guy’s stone score accurately predicted the SFR after PCNL. It is easy to use and reproducible. It is an objective and reliable method for describing the complexity of PCNLs when predicting the SFR and reporting results.The S.T.O.N.E. nephrolithometry score provides preoperative information for each case, providing a framework for standardized academic reporting. The S.T.O.N.E. nephrolithometry score can predict the stone-free status and can be used as an adjunct for surgical planning and also patient counseling. Predicting which patients are likely to be rendered stone free or those who will have a residual stone burden, need additional staged procedures. Additional validation of this scoring system with external data is important to confirm its general applicability for PCNL.Both Guy’s and S.T.O.N.E scoring systems have comparable accuracies in predicting post-PCNL stone-free status. Other factors not included in either scoring system may need to be incorporated in the future to increase their accuracy. |
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