Evaluation of Outcome of Ureteroscopic Pneumatic Lithotripsy in Single Lower Ureteric Calculus and Its Association with CT Parameters

Objective: To evaluate the outcome of ureteroscopic pneumatic lithotripsy in single lower ureteric calculus and correlate its success with different CT parameters like HU, size of calculus and hydrnephrosis, if present. Patients and Methods: This study was conducted from October 2017 to March 2019 in Department of General Surgery, Maulana Azad Medical College, New Delhi. 30 patients (out of which 6 were excluded due to spontaneous passage of calculus), with single lower ureteric calculus were chosen and the outcome of URSL was compared with respect to CT parameters of Size, HU and Hydronephrosis and intra-operative clearance of calculus. Results: Success rate of URSL in single lower ureteric calculus was found to be 75%. Lower HU (774.12 ± 212.85) was associated with higher success rate. Similarly smaller size of calculus (9 ± 2.1) mm was associated with success group. Patients with gross hydronephrosis had a poor outcome of URSL. Lower urinary tract infection (8.33%) was the most common complication. Conclusion: Patients with small size calculus, low HU and absence of hydronephrosis have a better outcome of URSL.


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.

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.   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.

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).

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.      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  [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.

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.