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The Development of Upper Urinary Tract Stones In Patients with Neural Tube Defects: Impact of Bladder Augmentation

Monday, October 22, 2012: 4:02 PM
Grand Ballroom B (Hilton Riverside)
Heidi A. Penn, MD, Douglass B. Clayton, MD, Stacy T. Tanaka, MD, John C. Thomas, MD, John C. Pope IV, MD, John W. Brock III, MD and Mark C. Adams, MD, Division of Pediatric Urology, Monroe Carell Jr. Children's Hospital at Vanderbilt, Nashville, TN

Purpose:   Patients with neurogenic bladder are known to be at increased risk of developing upper urinary tract stones.  We hypothesized that patients with lower urinary tract stone disease are at greater risk of developing upper urinary tract stones. 

Methods:   We performed a retrospective review of all patients seen over a 10 year period at our institution with neurogenic bladder due to a neural tube defects or caudal regression.  Patients were selected from a de-identified institutional database using 8 separate ICD-9 codes.  Inclusion criteria consisted of at least 24 months of urology follow-up, > 5 years of age at last follow-up visit, radiographically confirmed upper urinary tract stones, and confirmed diagnosis of neural tube defect or caudal regression. Univariable analysis was performed by Fisher's exact test and the Mann-Whitney U test. Multivariable Cox regression analyzed stone risk factors in patients following bladder augmentation. P values < 0.05 were considered significant.

Results:   287 patients were included and 49 developed upper urinary tract stones at our institution.  The prevalence of upper tract stones was 17% and median age at diagnosis was 19.1 years (range: 3.9 – 47).  Table 1 compares characteristics of stone formers and non-stone formers.  The presence of bladder augmentation with bowel was significantly higher in stone formers. 28% with a bladder augment developed a stone versus 10% without.  Median time to stone formation following bladder augmentation was 83.8 months (range: 23.8 – 159.5).   Cox regression in 77 patients with a bladder augment examined 5 factors 1) age at augment surgery, 2) gender, 3) neurologic lesion level, 4) ambulatory status, and 5) presence of lower urinary tract stones prior to, or at the time of upper tract stone diagnosis.  The analysis revealed the presence of lower urinary tract stones as the sole significant factor (p = 0.02) associated with upper urinary tract stone formation.    

Conclusion: Upper urinary tract stones occur frequently in patients with neural tube defects.  The placement of bowel into the urinary tract appears to increase this risk significantly.  Additionally, the presence of lower urinary tract stones may herald the development of an upper tract stone.  Patients undergoing bladder augmentation with bowel segments should be studied prospectively to better understand the natural history of upper urinary tract stone development.              

Table 1: Characteristics of Stone Formers and Non Stone Formers

Characteristics

Stone Former (n = 49)

Non Stone-Formers ( n =238)

P value

Mean Age at Last visit

27.5

16.5

< 0.0001

Mean Followup (mos)

113

101

0.12

Male

51%

43%

0.43

Caucasian

95%

80%

0.006

Bladder Augmentation

59%

25%

<0.0001

CIC  without Bladder Augment

40%

51%

0.48

Bladder Stones

51%

7%

<0.0001

Lumbar Level Lesion or Lower

75%

82%

0.31

Ventriculoperitoneal Shunt

83%

78%

0.44

Wheelchair dependent

85%

52%

<0.0001