Urinary stasis, elevated intravesical pressures, and UTIs have all been postulated to contribute to the development of urinary tract stones within the neurogenic bladder. Up to 90 % of patients with open MMC defects and 66 % of closed defects have abnormal bladder function on urodynamic testing [24]. Symptomatic bladder dysfunction has an estimated prevalence of 16 % in the cerebral palsy population, with asymptomatic dysfunction as high as 30 % [32]. MMC patients that developed urolithiasis are less likely to be spontaneous voiders and more likely to have undergone bladder augmentation or urinary diversion [62]. No literature exists regarding the development of urolithiasis in cerebral palsy patients with bladder dysfunction.

Lower urinary tract reconstruction is a common procedure of those with neural tube defects, exstrophy-epispadias complex, and PUV. These patients are at risk of forming stones for a variety of reasons including presence of foreign material such as absorbable staples, mucous production from intestinal segments, urinary stasis, and infection [17]. Urine retention appears to be the most important risk factor for bladder stone formation as spontaneous voiders have the lowest rate of stone formation [17, 36].

Although the rate of lower urinary tract surgery has decreased in the myelomeningocele population, 11–17 % of patients have undergone diversion or augmentation [20, 64]. However, of MMC patients that formed stones, 33–38 % had undergone urinary diversion or bladder augmentation [13, 62]. Bladder reconstruction is also associated with upper tract stones. Of patients with MMC that form upper tract stones, up to 73 % had lower urinary tract reconstruction [56].

A variety of urological procedures have been employed to manage bladder exstrophy. Ureterosigmoidostomy (USS) was once a popular method of management for exstrophy and long-term follow-up showed that up to 40 % of USS managed patients developed recurrent urolithiasis [12]. Procedures that aimed to provide continence through a bladder neck reconstruction increased the risk of stone formation, with 94 % of exstrophy patients with stones having undergone a bladder neck procedure while only 43 % of non-stone formers have undergone a bladder neck procedure. Bladder augmentation also contributes to stone risk with 46 % of augmentation cystoplasty exstrophy patients having formed stones as opposed to only 15 % of nonaugmented exstrophy bladders. Up to 90 % of urolithiasis in exstrophy patients is lower urinary tract in origin [54]. Reconstructive surgery places patients at risk of forming urinary tract stones.

Within the general population, approximately 10 % of stones are struvite stones indicating an infectious cause [27]. In contrast, up to 30 % of exstrophy patients and 39–100 % of MMC patients had struvite stones on composition analysis [13, 46, 54, 62]. Fifty-three percent of exstrophy stone formers had UTIs on presentation and having an infection significantly increases the likelihood of diagnosis of bladder stones, as well as recurrence of bladder stones [54]. In patients who have undergone augmentation enterocystoplasty, all stone formers were found to have persistent bacteriuria as opposed to 75 % of non-stone formers [36], and stone formers also have an elevated urine pH [15]. In MMC patients, 64–75 % of stone formers had a history of UTIs, while 30–38 % of MMC patients overall had previous UTIs [13, 62]. While the presence of calculi and rates of UTIs are strongly associated, whether infections beget stones or stones beget infections (or both) has not entirely been determined. Patients with reconstructed bladder and recurrent or escalating infections should be evaluated for the presence of a stone.

Adult MMC patients have an obesity rate of 35–37 % which is significantly higher than reported for pediatric MMC patients [9]. Obesity is a known risk factor for stone formation with a BMI over 30 conferring a relative risk of 1.3 in men and up to 2 in women [4, 61]. Obese patients are known to excrete higher concentrations of sodium, phosphate, and uric acid; however, urine pH decreases with increasing body weight [26, 43, 52]. As such, obese patients have a higher proportion of uric acid stones [5, 10]. For obese patients with other risk factors, like nonweightbearing status, prior terminal ileal resection, or chronic bacteriuria, uricaciduria may represent an additional risk factor.

Hypercalciuria is a known lithogenic risk factor for the development of calcium kidney stones. Patients with spinal cord injuries develop elevated levels of urinary calcium in the first few months following injury as a result of immobilization leading to bone resorption [57]. Evidence regarding hypercalciuria in patients with myelomeningocele and cerebral palsy is limited, with studies limited to the pediatric population. Okurowska-Zawada et al. [38] demonstrated that hypercalciuria is associated with bone fractures in those with myelomeningocele. Indeed, nonambulating MMC patients have a higher level of urinary calcium excretion [44]. Shaw et al. examined osteopenia in immobilized cerebral palsy patients and found three of nine patients with hypercalciuria [51]. Immobilization is a risk factor for the development of upper tract stones in MMC patients [56]. The higher rates of immobilization in MMC and CP patients may place them at risk of developing hypercalciuria and calcium-based urolithiasis.

Congenital obstructive uropathy, most commonly secondary to PUV, can be a devastating condition. Between 22 and 32 % of pediatric and young adult patients with PUV will progress to end stage renal disease (ESRD) [16, 41]. Studies investigating rates of progression to ESRD in the adult population with PUV are lacking. Kamal et al. [21] found that PUV was the underlying disease in 7 % of kidney transplantations at their center. Adult transplanted kidneys have an incidence of stones anywhere from 0.4 to 1.3 %, a rate lower than the general population. The low rate of lithiasis in allograft kidneys is speculated to be a result of the high level of donor screening, eliminating stone forming kidneys from the donor pool [1, 11, 23, 59]. In the pediatric transplant population, the incidence may be slightly higher, up to 2.5 % [22, 35]. It is important to note that a transplanted kidney is denervated, so spontaneous passage may go unnoticed. This may represent an important reason why the incidence of kidney stones is lower in transplanted kidneys [11]. While the risk of stone formation within the adult population of PUV patients is not well studied, patients with a history of PUV often have dysfunctional bladders with elevated rates of bacteriuria and UTI related to retained hydronephrotic native kidneys, incomplete bladder emptying, and the need for intermittent self-catheterization (ISC).

Initial evaluation of the stone formers should include some basic laboratory tests. Stone analysis, if available, can allow for targeted medical management. Imaging for current or residual stone should be done. Non-contrast CT scan can be used for diagnosis and evaluation of any anatomic abnormalities. Initial serum tests should include serum calcium and uric acid as well as urinalysis with pH and urine culture, all of which can give an indication to underlying metabolic reasons behind stone formation.

Comprehensive metabolic evaluation including 24 h urine chemistry should be considered in all patients with recurrent urolithiasis. In a study comparing stone formers to non-stone formers having undergone enterocystoplasty, stone formers were more likely to have elevated urinary calcium and pH and decreased urinary citrate and volume [15]. Hypercalciuria may also be seen as a result of osteodystrophy in patients that are nonambulatory such as those with cerebral palsy and MMC [38, 44].

No studies have been done examining diets in adult patients with congenital urologic disorders. The distribution of stone composition varies from the general population and thus, dietary recommendations may differ from the general population. These patients have a high rate of both calcium phosphate and struvite stone formation and this should be considered when giving any empiric dietary recommendations [13, 46, 54, 62]. However, metabolic evaluation including 24 h urine chemistry and stone composition remains the standard for guiding individualized dietary recommendations.

Importantly, patients with neurogenic bladder from MMC likely also have slow bowel transit and if they have previously had terminal ileal resection or resection of a large segment of their absorptive bowel, may have malabsorption.

Medications to be used will be based on laboratory evaluation including 24-h urine electrolytes and stone composition. Recurrent UTIs are an important risk factor for recurrent stone formation within this patient population, and prophylactic antibiotics might be considered for prevention of stones [54, 62]. However, some recommend against this as a strategy as it increases the risk of developing drug-resistant organisms [40]. One study found a relationship between methane, small intestinal bacterial overgrowth, and recurrent UTIs in MMC patients. Intestinal decontamination with antimicrobials may play a role in preventing recurrent UTIs [37]. Currently, no studies have focused on the role of antibiotic prophylaxis in stone prevention in these patients.

Elevated urinary calcium can be a risk factor within this population. Patients that had bladder augmentations and form stones have higher levels of urine calcium [15]. Spina bifida and cerebral palsy patients that are immobilized and form stones often have elevated urinary calcium [44, 51]. Hydrochlorothiazide was studied as a method to prevent osteodystrophy in immobilized MMC patients. The study suggested that hydrochlorothiazide did not improve bone mineral density but was shown to decrease urinary calcium levels [45]. How effective hydrochlorothiazide is at reducing stone formation within immobile patients remains to be studied.

Adult MMC patients have a high obesity rate putting them at risk of uric acid stones. Uric acid stone formers often have urine chemistries showing normal uric acid but low urine pH [49]. For a stone >4 mm, a hounsfield unit density of ≤500 on computed tomography and a urine pH ≤5.5 has a positive predictive value of 90 % for uric acid composition [55]. Allopurinol can be considered to further decrease the urine uric acid concentration. However, the more important risk factor is urine pH which decreases the solubility of uric acid [5, 26, 43, 52]. Potassium citrate or bicarbonate can be considered in these patients to increase the urine pH. This treatment may be especially effective in MMC patients who already have metabolic acidosis from chronic renal insufficiency and/or respiratory acidosis from the myriad of pulmonary conditions to which they are prone, although efficacy remains to be determined in well-designed studies.

Spontaneous voiding is the optimal bladder management for preventing the formation of stones [62]. However, in those with bladder dysfunction, methods to reduce urine retention should be employed. Currently, ISC is considered the gold standard for management of the neurogenic bladder [58]. No randomized controlled studies have been done comparing ISC and chronic indwelling catheters [18]. In retrospective studies, chronic indwelling catheters increase the risk of bladder stone formation [3, 31, 39].

One method shown to potentially reduce the risk of stone formation in augmented bladders is the use of bladder irrigation. Patients having undergone bladder augmentation were instructed to wash twice weekly with 240 mL of saline and once weekly with a gentamicin sulfate solution (240–480 mg/L) at a volume of 120–240 mL. Only 7 % of patients undergoing this protocol formed stones as opposed to 43 % undergoing standard ISC. However, compliance with bladder irrigation may prove difficult, particularly among adolescent and young adult patients [17].