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Background
Management of primary vesicoureteral reflux (VUR) remains controversial, and reflux grade currently constitutes an important prognostic factor. Recent work suggests the distal ureteral diameter ratio (UDR) may be more predictive for assessing outcomes than VUR grade. We performed an external validation study in young children, evaluating spontaneous resolution rates relative to reflux grade and UDR.
Methods
Voiding cystourethrograms (VCUGs) of children with primary VUR were reviewed. The largest ureteral diameter within the true pelvis was measured and normalized by dividing by distance from the L1-L3 vertebral body giving the UDR. Reflux grade and UDR were tested in uni- and multivariate analysis. Primary outcome was status of VUR at last clinical follow-up (i.e. resolution, persistence or surgical intervention). Patient demographics, timing of reflux, laterality, and indication for imaging were also assessed.
Results
One hundred and forty-seven children (98 girls, 49 boys) were diagnosed with primary VUR at a mean age of 5.5 ± 4.7 months. Of the 147 patients, 67 (45.6%) resolved spontaneously, 55 (37.4%) had persistent disease at the end of the follow up period and 25 (17%) were surgically corrected. Median time to resolution (censoring patients at the time of surgical correction or those with persistent disease) was 21.5 months (95% CI 17-25 months). Patients who spontaneously resolved had significantly lower VUR grade, refluxed later in the bladder cycle, and had a significantly lower UDR [Table]. In a multivariate model, grade of VUR (p = 0.001), age less than 12 months (p = 0.008), and UDR (p < 0.0001) retained statistical significance. For every 0.1 unit increase in UDR, there was a 2.6 (95% CI 1.58-4.44) increased odds of persistent disease. Likewise, for every unit increase in grade, there was a 1.6 (95% CI .9-3.0) increased odds of persistent VUR.
Conclusions
UDR correlates with reflux grade, but is more predictive of spontaneous resolution in children with primary VUR. UDR is a readily accessible, objective measure of VUR, and provides valuable prognostic information about spontaneous resolution, facilitating more individualized patient care.

Variable	Overall (n = 147)	Resolved (n = 67)	Persistent (n = 55)	Surgical Correction (n = 25)	P
Gender, n (%)					0.4941
Male	49 (33.3)	19 (28.4)	21 (38.2)	9 (36.0)
Female	98 (66.7)	48 (71.6)	34 (61.8)	16 (64.0)
Bilateral, n (%)					0.0535
No	59 (40.1)	34 (50.7)	18 (32.7)	7 (28.0)
Yes	88 (59.9)	33 (49.3)	37 (67.3)	18 (72.0)
High Grade VUR, n (%)					<0.001
No	103 (70.1)	61 (91.0)	37 (67.3)	5 (20.0)
Yes	44 (29.9)	6 (9.0)	18 (32.7)	20 (80.0)
Reflux grade, M (SD)	2.97 (1.08)	2.40 (0.89)	3.13 (0.94)	4.12 (0.73)	<0.001
Reflux grade, n (%)					.0005
1	6 (4.1)	4 (6.0)	2 (3.6)	0 (0)
2	46 (31.3)	35 (52.2)	11 (20.0)	0 (0)
3	51 (34.7)	22 (32.8)	24 (43.6)	5 (20.0)
4	31 (21.1)	5 (7.5)	14 (25.5)	12 (48.0)
5	13 (8.8)	1 (1.5)	4 (7.3)	8 (32.0)
Time of Reflux, n (%)					<0.001
Voiding only	16 (10.9)	9 (13.4)	6 (10.9)	1 (4.0)
Late filling	93 (63.3)	54 (80.6)	30 (54.5)	9 (36.0)
Early to mid filling	38 (25.9)	4 (6.0)	19 (34.5)	15 (60.0)
Age Group, n (%)					0.0668
<1yr	131 (89.1)	62 (92.5)	49 (89.1)	20 (80.0)
1yr +	16 (10.9)	5 (7.5)	6 (10.9)	5 (20.0)
Age, M (SD)	5.53 (4.71)	6.07 (4.68)	5.05 (3.70)	5.15 (6.53)	0.4440
UDR, M (SD)	0.28 (0.16)	0.19 (0.08)	0.31 (0.14)	0.45 (0.18)	<0.001