Augmentation cystoplasty is the gold standard treatment of patients with myelodysplasia with poorly compliant and overactive bladders not responsive to conservative measures. In addition to helping preserve the upper urinary tract, this procedure also allows many patients to achieve continence as well as independence, especially when combined with a bladder channel. However, despite being the best available option for many, it is not without significant morbidity.1 Urinary tract stones frequently develop in patients with myelodysplasia who have undergone augmentation cystoplasty, with a reported incidence rate of 6% to 53% and a subsequent recurrence rate of 19% to 44%.2-11 Because of the high incidence of stones, it is recommended that patients undergo annual radiographic evaluation for stones after enterocystoplasty.7
Reported risk factors for stone development that are pertinent to this patient population include recurrent urinary tract infections, lower urinary tract reconstruction utilizing bowel, procedures that increase bladder outlet resistance, abdominal wall stoma, urinary stasis, mucus production, immobility, sensory impairment, vesicoureteral reflux, renal scarring, a thoracic-level spinal defect, other anatomic abnormalities (such as cloacal malformations), metabolic abnormalities (including acidosis), lower urine output, family history, poor nutrition, and indwelling catheter.2,3,13-16 The reported benefit of an irrigation protocol to prevent lower urinary tract stones varies.6,8
Due to the high prevalence of stones in patients with myelodysplasia who have undergone augmentation cystoplasty, it is helpful to know preoperatively which patients are at highest risk of developing stones. This knowledge can change the preoperative assessment and counseling, and help direct postoperative imaging studies. Additionally, by reducing the frequency of imaging in patients at low risk of stones, this can potentially save healthcare dollars. However, to date, there are no known preexisting factors that have been identified that increase the risk of developing urinary tract stones after this procedure.4
The goal of this study is to determine the incidence of stone development in our patients with myelodysplasia who have undergone augmentation cystoplasty, as well as to identify any risk factors for this occurrence.
Most of the patients with myelodysplasia at Children’s of Alabama (Birmingham, AL) are enrolled in the Center for Disease Control National Spina Bifida Patient Registry. This provides a prospective and retrospective database of 435 patients, of whom 54 (12.4%) have undergone ileal augmentation cystoplasty for management of a neurogenic bladder. We excluded any patient who had undergone augmentation cystoplasty at other institutions because the operative notes, dates of surgery, and preoperative laboratory values were not available. We also excluded patients who had undergone renal transplantation due to concern that their renal function and medications could be a significant confounding factor. Of the initial 54 patients, 40 patients met all inclusion criteria. No patient had a history of urinary tract stones prior to augmentation cystoplasty. All patients and families were instructed to perform clean intermittent catheterization (CIC) at least four times daily and to irrigate their augmented bladders on a daily basis.
Imaging reports, clinic notes, and operative reports were reviewed for all 40 patients to identify those patients who developed urinary tract stones. The number of stones, stone events, and stone interventions were recorded. For all patients, we also reviewed patient demographics, medical history, surgical history, reported compliance with catheterization and irrigation, and all available laboratory values before and after surgery. Potential risk factors for stone development were then evaluated. This included the following laboratory values before and after bladder augmentation: hematocrit, blood urea nitrogen, serum creatinine, serum chloride, serum bicarbonate, serum calcium, and serum glucose. The laboratory values drawn during preoperative assessment and the most recent results were used for the pre- and postoperative laboratory values. Simultaneous procedures that could potentially increase the risk of stones, including creation of bladder channel, ureteral reimplantation, and bladder neck sling, were included in the analysis. Patient demographics, including sex, level of lesion, ambulatory status, body mass index, age at augmentation, and time in follow-up were reviewed. Factors that could indicate compliance or extent of disease, including bladder and bowel continence, reported compliance with CIC, history of bladder rupture, presence of hydronephrosis, and history of ulcers or skin breakdown were also evaluated. Statistical analysis included multivariate and univariate analysis using bootstrap resampling, nonparametric analysis, Pearson’s Χ2 test, and Student’s t-test.
The patients who met inclusion criteria included 23 girls and women, and 17 boys and men, comprising 1 Asian patient, 5 black patients, and 34 white patients, with an average age of 15 years (range, 6-24 y). The level of lesion was sacral in 9 patients, thoracic in 10, and lumbar in 21. Of the 40 patients, 15 (37.5%) developed stones at a mean of 26.9 months after augmentation (range, 5-85 mo). Fourteen patients developed bladder stones and 1 developed a solitary renal stone. Ten patients (66.6%) had a solitary stone event, whereas 5 (33.3%) developed recurrent stones; the recurrent stones were all bladder stones. The patient with the renal stone never developed a bladder stone. The stone incidence per year was 6.8%; 19 procedures were performed for the management of these stones: 10 open and 9 endoscopic. Observation was chosen for the patient with the renal stone.
Laboratory values were available for 21 of the 25 patients (84%) without stones and for 13 of the 15 patients (87%) with stones. Multivariate analysis demonstrated that the strongest risk factor for development of urinary tract stones after augmentation was the difference in serum chloride before and after augmentation (–0.25 in the stone-former group, 2.68 in the stone-free group) with a percentage of the best model of 39.8%. This was also significant in nonparametric analysis (P = .02). Multivariate analysis showed that the combination of female sex and a decrease in serum chloride after augmentation were the best two predictors of stone development (percentage of the best model, 26.8%); the best three predictors were female sex, decrease in serum chloride after augmentation, and longer follow-up after augmentation (percentage of the best model, 12.9%; Table 1). However, longer follow-up and female sex did not meet significance on univariant analysis (Table 2).
A total of 38% of our patients developed urinary tract stones after augmentation cystoplasty and 12.5% developed recurrent stones. Our initial stone formation rate is consistent with what is reported in the literature (6%-52%). This also holds true for stone recurrence (19%-44%).2-9
Most stone formers developed bladder stones, whereas only one patient developed a solitary renal stone. Other studies, such as the series by Schlomer and colleagues9 and Khoury and colleagues,12 also found that the majority of stones formed after augmentation cystoplasty are bladder stones.
We found that the most significant risk factor for developing stones after surgery was a decrease in serum chloride in follow-up after augmentation. We also showed that bowel continence is highly associated with the development of stones. Our theory is that those who develop stones likely have contraction alkalosis from dehydration, which not only leads to development of stones, but also leads to some constipation and, therefore, bowel continence. Reduction in serum chloride occurs with contraction alkalosis. The strength of this theory would have been enhanced if there had been a statistically significant difference in serum bicarbonate between those who formed stones and those who did not. Nevertheless, the importance of hydration should be emphasized in this cohort. Although this has not been specifically noted in other studies to our knowledge, Robertson and Woodhouse17 found that patients who developed stones after enterocystoplasty had elevated urinary pH (mean, 6.93) and low urine volume, which is consistent with the same metabolic state. However, in the study by Hamid and associates,16 the urine of the patients who developed stones after enterocystoplasty demonstrated a significantly lower urinary pH level than those who did not form stones (6.49 vs 6.93). Their study did demonstrate that patients who develop stones had significantly lower urine volume and lower fluid intake than those who did not form stones, which are both consistent with dehydration.16 A limitation of our study is that we did not assess urine volume.
We did not find that the concurrent surgeries were significantly related to stone development. Although other studies have shown that the creation of a bladder channel is associated with an increased risk of stones, in our study the patients who developed stones were actually less likely to have a bladder channel (47% of patients with stones had bladder channels vs 60% of those without stones), although the difference was not significant (P = .41).3,12 Although others have reported that concomitant bladder neck closure/reconstruction was associated with stone risk, this was not true in our series.3
Interestingly, patient- and family-reported noncompliance with CIC and irrigations was not associated with an increased risk of stones. This latter finding may be reflective of the utilization of patient- and family-reported compliance. Of note, none of the stone formers had a history of bladder rupture.
There are, undoubtedly, other patient factors not identified in this study that could contribute to the development of lower urinary tract stones in these patients. Candidates include bone health, mobility, and urinary stone risk parameters.
Patients with spina bifida subjected to augmentation cystoplasty are at high risk for developing bladder stones, as well as recurrent calculi. We strongly advocate proper hydration to limit these events. Although our results did not demonstrate that compliance with CIC and irrigation reduced stone risk, we recommend that it be done.
