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Background: Upper tract inaccessibility limits performance of ureteroscopic stone extraction under one anesthetic in a significant percentage of children. In such cases, passive ureteral dilatation (pre-stenting) with later ureteroscopic stone extraction is necessary. Previous efforts to investigate the relationship between patient age, gender, BMI and the need to pre-stent yielded no definitive associations, but sample sizes were small. This study sought to examine factors associated with pre-stenting and evaluate for any association between pre-stenting and stone outcomes.
Methods: With IRB approval, all pediatric patients undergoing ureteroscopy for stone management by 7 pediatric urologists from 2009 - 2015 were identified. Children with complex urologic histories/anatomy or comorbid conditions mandating pre-stenting (i.e. UTI) were excluded. Thus this study was limited to uncomplicated attempts at ureteroscopy for urolithiasis in otherwise healthy children. Ureteroscope and/or access sheath passage was attempted in all and decision to pre-stent was made by each individual surgeon. Demographic and stone characteristics were compared in the pre-stented and not pre-stented group. Factors associated with being pre-stented were evaluated with univariable and multivariable logistic regression.
Results: There were 124 ureteroscopy cases included with 11 bilateral cases for a total of 135 ureteroscopies included (Table 1). Overall, 30% of ureters were pre-stented. Pre-stent rates varied by surgeon (0 - 59%) and approached statistical significance on univariable analysis (p = 0.07). On multivariable analysis (Table 2), a 10% higher BMI percentile was associated with 0.8 times the odds of being pre-stented (95% CI: 0.7 - 0.9, p<0.001). Increasing stone size and stone position above the distal ureter/UVJ were associated with increased odds of being pre-stented (OR: 1.2 [1.02 - 1.31], OR: 6.0 [1.3 - 27.9], respectively). Both groups had similar operative times and stone free rate, defined as no stones seen on follow up imaging (typically renal u/s). Pre-stenting did not significantly alter ability to place a ureteral access sheath.
Conclusions: About 30% of children undergoing ureteroscopy are pre-stented at our institution. More proximal stone position, larger stone size, and lower BMI percentile were associated with being pre-stented. Rates of pre-stenting were highly variable by surgeon. Pre-stenting was not associated with improved stone free rates, operative times, or successful placement of a ureteral access sheath; in essence, pre-stenting provided no additional benefit beyond ureteroscope access in this otherwise uncomplicated population. This information can be used to counsel families and we recommend that a pre-stenting in patients without a UTI be performed only after initial attempt at ureteroscopy.

Table 1: Comparison of pre-stented and not pre-stented groups
	Pre-stented (n = 40)	Not Pre-stented (n = 95)	P-value
Age yrs	12.7 (4.5)	14.2 (3.6)	0.51
BMI Percentile	43% (34%)	65% (31%)	0.0041
Gender			0.62
Male	22 (55%)	57 (60%)
Female	18 (45%)	43 (40%)
Race			0.42
White	29 (73%)	55 (58%)
Black	2 (5%)	4 (4%)
Hispanic	8 (20%)	34 (36%)
Other	1 (3%)	2 (2%)
Stone Location3			0.32
Renal	28 (71%)	58 (62%)
Proximal Ureter/UPJ	2 (5%)	5 (5%)
Mid. Ureter	4 (10%)	5 (5%)
Distal Ureter/UVJ	5 (13%)	25 (27%)
Stone Size in mm3	6.4 (3.9)	5.4 (3.2)	0.11
Surgeon			0.072
1	18	46
2	3	15
3	4	9
4	3	4
5	2	11
6	10	7
7	0	3
Operative time (hrs)	1.8 (0.9)	1.8 (0.8)	0.91
Access sheath attempted and placed?	27/30 (90%)	53/62 (85%)	0.42
Stone free on follow up imaging?3	22/34 (65%)	52/80 (70%)	0.92
Continuous data presented as mean (SD), categorical data presented as n(%) 1Two-tailed t-test 2Fisher Exact test 32 missing stone size, 3 missing stone location, 21 missing follow up imaging

Table 2: Multivariable analysis of factors associated with being pre-stented
	Univariable OR (95% CI)	P-value	Multivariable OR (95% CI)	P-value
Age1	0.9 (0.8-1.0)	0.06	0.9 (0.8-1.0)	0.08
BMI percentile2	0.8 (0.7-0.9)	0.001	0.8 (0.7-0.9)	<0.001
Stone location3	2.5 (0.9-7.1)	0.09	6.0 (1.3-27.9)	0.02
Stone size4	1.1 (1.0-1.2)	0.2	1.2 (1.0-1.3)	0.03
Surgeon5	3.7 (1.5-9.2)	0.005	12.5 (3.3-47.1)	<0.001
1OR for 1 year increase in age 2OR for 10% increase in BMI percentile 3OR for distal ureter/UVJ vs proximal to distal ureter/UVJ 4OR for 1 mm increase in stone size 5OR for surgeons with >40% pre-stent rate