Evaluation of Outcome of Ureteroscopic Pneumatic Lithotripsy in Single Lower Ureteric Calculus and Its Association with CT Parameters ()
1. Introduction
Ureteral stones are common (5% - 12%) urologic condition [1]. They are commonly made up of Calcium salts, while others are also made of other compounds like triple phosphates, cysteine and uric acid [2]. Due to this variability in its composition, the stones themselves can occur in various shapes, sizes and hardness. The stone may lie at different anatomical positions within the ureter, hence they are also classified as upper, middle and lower ureteric stone. Lower ureteric calculus (distal ureter + UVJ) is most common, more than 60% of all ureteric calculus [3].
Non Contrast Computed Tomography (NCCT) is accepted as one of the best imaging modality for detection and evaluation of ureteric calculus with sensitivity as high as 96% [4]. It is the imaging modality of choice during acute renal colic. Other than the anatomical details, we can rule out other pathologies that may mimic renal colic [5]. CT also helps in knowing about the nature or the hardness of the stone measured in terms of Hounsfield unit (HU) [6] [7]. In terms of position it tells the exact distance of the stone from PUJ/VUJ.
Ureteroscopic lithotripsy (URSL) is a good intervention modality for treatment of ureteric stones [8]. Its outcome is affected by size, position and nature of stones. In our study we are evaluating the outcome of URSL in lower ureteric calculus and its association with CT parameters. The parameters used are dimensions and HU of stone which depict the nature and size of stone.
2. Material and Methods
The study was conducted in department of General Surgery, Maulana Azad Medical College and Lok Nayak hospital, New Delhi from October 2017 to March 2019. It was a prospective study. A total of 30 patients were taken for study, which was done for a period of 1.5 years. Inclusion criteria was all adults (>18 years) with diagnosis of single lower ureteric calculus on X-Ray KUB (Figure 1). Exclusion criteria were presence of ureteral injury/stricture, urinary tract infection, single kidney, renal failure. Out of the 30 patients, 6 were excluded due to spontaneous passage of stone. Remaining 24 patients underwent unenhanced helical computed tomography scan (Figure 2 & Figure 3). The images were reviewed at a Picture Archiving and Communication System (PACS) workstation.
The size of the stone was measured using the dimension tool of Radiant DICOM software. The longest transverse diameter of stone was taken as the size of stone. Other stone factor used was height of stone in form number of axial cuts images of stone (slice thickness 5 mm). The Hounsfield units (HU) for each stone were calculated for the cross-section with the largest diameter and the secondary sign like hydronephrosis was graded between 0 - 3. All the CT studies were reviewed by radiologist who was blindfolded to pre and postoperative CT parameters.
Hydronephrosis was graded as follows: 0 = absent, 1 = prominence of the intrarenal pelvis or mild ureteral dilatation, 2 = dilatation of the renal calices or moderate ureteral dilatation, and 3 = severe dilatation of the collecting system [9].
Using a 10 F rigid ureteroscope, a guide wire was introduced in lower ureter and ureteroscope was advanced in lower ureter. Using pneumatic lithotripter the stone was broken and extracted using dormia basket or forceps.
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Figure 1. X-Ray KUB showing right lower ureteric calculus.
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Figure 2. CT KUB showing right lower ureteric calculus.
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Figure 3. CT KUB with calculus in right lower ureter.
Statistical analysis was performed to evaluate the association between the outcome of URSL and patient’s age and gender. We also evaluated the association between the outcome of URSL and CT parameters of the stone like size of the stone, Hounsfield unit. We also included hydronephrosis as secondary sign, duration and complication of the procedure as statistical parameters in our study.
All values are expressed as the mean ± standard deviation. Categorical variables were presented in number and percentage (%) and continuous variables were presented as mean ± SD and median. Normality of data was tested by Kolmogorov-Smirnov test. If the normality was rejected then non parametric test was used. Analysis was done using Statistical Package for Social Sciences (SPSS) version 21.0. A p value of less than 0.05 was considered significant.
3. Results
Data from 24 patients with single lower ureteric stone were analyzed. Outcome was classified as successful or failure, based on intra-operative clearance of stone and post operative CT findings. In our study 18 patients had complete removal of stones and 6 patients had failed outcome of URSL. The overall rate of treatment success was 75% (n = 18) and the failure rate was 25% (n = 6). The outcome of URSL was correlated with duration of the procedure and CT parameters such as size of stone (diameter and height), Hounsfield unit and presence of hydronephrosis. In group 1 (success group) the mean duration of URSL was 25.56 ± 6.49 minutes and mean Hounsfield unit of stone was 774.12 ± 212.85 HU. In group 2 (failure group) the mean duration of URSL was 40.75 ± 4.95 minutes and mean Hounsfield unit of stone was 1193.12 ± 327.51 HU (Table 1).
Out of 24 patients, 18 had positive outcome of URSL with mean size of stone 9 ± 2.1 mm and 6 had negative outcome with mean size of stone 12.5 ± 3.3 mm. The p value for stone size in relation to outcome was <0.0004 which was statistically significant (Figure 4).
In our study population the shortest duration of URSL was 15 min and the longest duration was 48 min. Out of 24 patients, 18 had positive outcome of URSL with mean duration of procedure 25.56 ± 6.49 and 6 had negative outcome with mean duration of 40.75 ± 4.95. The p value for procedure duration was <0.0001 which was statistically significant (Figure 5).
Out of total sample size of the study 58.33% of patients had moderate hydronephrosis (HDN), 29.17% had gross HDN and 12.50% had mild HDN. Patients with gross HDN had a poor outcome of URSL (Figure 6 & Figure 7).
The patient’s sex, age, height, weight, BMI and previous stone history did not differ significantly between group 1 and group 2 (Table 2).
The most common complication seen was lower urinary tract infection, which accounted for 8.33%. Second most common complication was hematuria which accounted for 4.16%. There was no evidence of any other known complication including ureteric perforation (Table 3).
4. Discussion
The success rate of URSL depends on the location of stone in the ureter, size of the stone, the use of surgical instruments including the ureteroscope, and the operator’s surgical technique.
The stone size factors that were included in the study were longest diameter, transverse diameter, and height by CT axial cuts. Most studies have focused on the longest stone diameter for measuring stone size. However, Abdelrahim et al. [10] considered the transverse stone diameter, as this dimension generates the most resistance to the downward force applied by a basket or forceps.
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Table 1. Comparison of outcome of URSL in respect to duration of procedure, size and HU of calculus and Hydronephrosis.
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Table 2. Comparison of various parameters in success and failure group.
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Figure 4. size of stone with outcome of URSL.
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Figure 5. Duration with outcome of URSL.
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Figure 6. Distribution of Hydronephrosis.
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Figure 7. Hydronephrosis and outcome of URSL.
There is still controversy whether the secondary signs can predict outcome in patients with ureteral stones or not. In a report on the incidence rates of secondary signs and their influences on patient management, Ege et al. [11] identified hydroureter, hydronephrosis, periureteral edema, and unilateral renal enlargement as the most reliable signs for endoscopic removal of stones. Takahashi et al. [12] reported that the severity of perinephric edema correlates with the probability of stone expulsion spontaneously. He also suggested that the degree of edema indicated the seriousness of ureteral obstruction. Seitz et al. [13] reported that the presence of secondary signs before URSL did not correlate with the preoperative stone-free rate. In our study 7 out of 24 patients had gross HDN and among them 6 had failed outcome of URSL. Patients with gross HDN had poor outcome of URSL. This was because patients with gross HDN has longer duration of stone disease which resulted in impaction of stone and thus resulting in failure of URSL.
In our study the stone with higher HU had a negative outcome as compared to stones with a low HU. The result was in concordance with the study done by Magnunson et al. [14] who showed that Hounsfield unit reflects the stone’s composition and hardness and correlates with the rate of successful ESWL.
Our study compares well with other world literature in terms of outcome of URSL. In our study the overall success rate was 75% and complication rate of 16.67%. Knispel et al. had a success rate of 73.7% in his series of 135 patients who were treated with lithocast [15] Shrestha et al. had a success rate of 88.5% in 52 patients with lower ureteric calculi when treated with pneumatic lithotripter [16]. Oktay et al. and Leidi et al. also showed the success rate of 91% in lower ureteric calculi [17] [18]. Another study done by Salman et al. compared pneumatic lithotripsy and laser lithotripsy. Out of 50 patients taken for pneumatic lithotripsy, 41 patients had successful outcome giving a success rate of 82% [19]. In our study we were not able to include the later complications such as stricture formation, which has been documented in literature, due to difficulties in the further follow up.
5. Conclusions
Size of the stone and Hounsfield units of the stone are the factors which directly influence the outcome of URSL; the bigger the stone or the higher the HU of stone, the less the chances of complete removal of stone. Gross hydronephrosis is associated with poor outcome of URSL.
This study also points towards higher incidence of ureteric stones in males as compared to females with mean age of presentation between 20 - 40 years. We found that ureteroscopy is safe with minimal complications in the management of lower ureteric calculus.
Ethical Clearance
Study was approved by institutional ethics committee.