Spina bifida is a major cause of neurologic bladder among children. Therefore, these children are followed urodynamics (UDS), renal scintigraphy and laboratory workups. However, these evaluation cannot be performed frequently because of its invasive. At present, invasive UDS is the gold standard test for assessment lower urinary tract function precisely. Ultrasound measurement of bladder wall thickness (BWT) has been proposed as a less invasive alternative to identify bladder abnormality. There is some emerging evidence in the literature that pathological conditions such as vesicoureteral reflux, detrusor overactivity, dysfunctional voiding and bladder obstruction, and neuropathic bladder may cause increase in BWT. However, there are few reports on BWT in children with spina bifida. The aim of the present study was to investigate whether BWT measured could be used to predict unfavourable findings in children with spina bifida.

We investigated 33 patients with spina bifida who underwent video urodynamics (VUDS) between August 2017 and January 2019. Exclusion criteria were previous urological operation such as bladder augmentation surgery, anti-reflux surgery. The median age of subjects was 13 years (range 1month-19years), and 48.5% patients were male. The characteristics of all patients are shown in Table 1. 
Table 1: Characteristics of all patients
Standard fluid cystometry was done with patients in the supine position using a 6Fr double lumen catheter and a rectal balloon catheter, filling at a rate of less than 10% of predicted bladder capacity per minutes. At filling cystometry, the parameters evaluated were first desire to void (FDV), bladder capacity and compliance. According to the definition proposed by the International Continence Society, detrusor overactivity (DO) was defined as any involuntary detrusor contractions during the filling phase which may be spontaneous or provoked and which the patient cannot completely suppress. Expected bladder capacity (EBC) for age was evaluated through the formula: EBC in ml, weight ×7ml (0-12 month), weight×10ml (13 month-24 month), and age × 30+30 (25 month-). 
BWT was calculated as the mean of the ventral and dorsal wall at the 0%, 20%, 40%, 60%, 80%, and 100% of EBC volume. Simultaneously with VUDS and BWT measurements were performed by ultrasonography using a 3.10Hz convex transducer. 
T-test and Pearson correlation test were used for analysing data. A value of P < 0.05 was considered statistically significant.

Median of FDV was 145 (range 85-482) ml, capacity was 240 (36-550) ml, and bladder compliance was 19.2 (1.3-190) ml/cmH2O. DO was present in 66.7% (22/33), vesicoureteral reflux (VUR) was present in 27.3% (9/33) of the VUDS performed. The mean parameters of BWT are shown in Table 2.
The BWT of the ventral wall was significantly lower than dorsal wall. It was showed that ventral BWT in patient with DO is significantly higher than patient without DO (20% of EBC volume). However, significant differences BWT in patient with between male and female was not found.

Table 2:  Bladder wall thickness parameters

This is the first report that VUDS and BWT multiple measurements were performed simultaneously. Measurement of BWT by ultrasonography is favourable as a non-invasive screening tool to evaluate for early bladder wall changes without radiation exposure. Almost all previous studies were performed to assess BWT only one point measurement. Moreover, selection of bladder volumes and which bladder wall for measurements in the BWT was an inconsistent method by each researcher. Therefore, BWT has been limited in its application due to a lack of standardized measurement criteria and reference values in children with neurogenic bladder.

Previous researches reported that the dorsal wall was slightly thicker than the ventral wall (1). In the current study, mean BWT was consistent with their report only 20% of EBC volume. This result indicates the possible presence of optimal bladder volume to assess bladder function.

The sex differences of BWT are still controversial. In our result, in all % of EBC volume, significant differences of BWT were not found between male and female. Actually we need more same age group data of both normal and pathophysiological status.
 
The increase of bladder contractions by DO may induce the hypertrophy of the bladder muscle over time. In neurogenic bladder patients, theoretically DO may contribute to the thickening of the bladder wall. However, there is no previous study which has evaluated in a standardized way the possible association between increased BWT and the presence of DO in children with spina bifida. In our results, only 20% of EBC volume, ventral BWT in patient with DO is significantly higher than patient without DO. This result also indicates the importance of optimal bladder volume to assess the bladder function. 
Up till now, there is no valid standard condition of measuring BWT. To be the standard test for assessment lower urinary tract function, appropriate measurement condition is needed.

The BWT may not correlate with the degree of detrusor dysfunction under our measurement conditions. BWT ultrasonography cannot identify bladder dysfunction of children with spina bifida and hence cannot be used to reduce the need for invasive UDS.

2006 Feb;175(2):704-8