Deformity of sacral vertebral arches in the conventional pelvic plain x-ray film is sometimes seen in children with persistent enuresis. This study is the first report of comparison of the images of three-dimensional computed tomography (3D-CT) in 2 cohorts; pediatric cases with enuresis and children without voiding symptoms or enuresis who underwent pelvic CT for other reasons.

From January 2019 to December 2019, 47 children with primary nocturnal enuresis underwent 3D-CT of sacrococcygeal bone (33 males, 14 females, mean age 7.9±2.0 years, range: 5 years-old to 13 years-old).  For the control group, 138 children without enuresis (78 males, 60 females, mean age 10.7±4.4 years, range: 3 months-old to 18 years-old) who underwent pelvic CT for other reasons were included. 
First, we evaluated the presence or absence of unfused sacral arches at S1-S3 levels in these two cohorts.  Then, we selected a subset age and gender matched enuresis children and control children without enuresis for a comparison study: Children with enuresis (n=32 in total, 21 males 11 females, mean age 8.0±2.2 years, range: 5 years-old to 13 years-old) and children without enuresis (n=32 in total, 21 males 11 females, mean age 8.0±2.2 years, range: 5 years-old to 13 years-old) were compared for fusion of dorsal sacral arms 3D-CT).

All procedures in this study involving human participants were performed in accordance with the ethical standards of the Institutional Review Board and the 1964 Helsinki declaration and its later amendments or comparable ethical standards. Informed consent was obtained from each child’s parents.

In the initial assessment in all participants, dysplastic sacral vertebral arches, evident as unfused arches at one or more levels of S1-S3 sacral arches, were observed in all cases of the enuresis group cohort (n=47) (Fig. 1A).  In the control group cohort (n=138), 77 children were over 10 years-old, among whom 70 cases (91%) showed fused sacral arches at all three S1 through S3 levels (Fig.1B) whereas the remaining 7 control children over 10 years-old (9%) had one or more unfused sacral arches at S1-S3 levels.  In addition, in the control group, 11 control children were under 3 years-old, and all of them showed three unfused sacral arches at S1-S3 levels. 
In the comparison study of age and gender matched enuresis patients and control children from 5 to 13 years-old (n=32 each), there was only one case (3%) in the enuresis group, in whom all S1-S3 arches were fused. Also, in the enuresis group, only one arch between S1 and S3 levels was fused in 7 cases (22%), and two arches were fused in 11 cases (34%). In contrast, in the control group, 19 out of 32 control children (59%) had fused arches at all S1-S3 levels (P< 0.0001 vs. enuresis group; student t-test) (Table 1). In addition, in the remaining control children who had unfused arches, sacral arches were not fused at any of 3 levels in 2 cases (6%), one arch was fused in 3 cases (10%), and two arches were fused in 3 cases (10%).

The etiology of primary pediatric nocturnal enuresis is controversial and objective diagnostic test is lacking. We hereby provide evidence for a novel hypothesis that dysplastic development of sacral bone, with occult neurological dysfunction, might be a cause of pediatric enuresis. We also found that, in the control group, the majority (91%) of children over 10 years-old showed fused sacral arches at all 3 sacral levels whereas there were no such cases among those younger than 3 years-old, suggesting that sacral arch fusion is gradually completed during childhood development.

Sacral vertebral arches at S1-S3 levels are normally fused by age 10 in most children. However, our study indicates that children with nocturnal enuresis exhibited a significantly higher incidence of unfused sacral arches than age and gender matched children without enuresis. Our results suggest that dysplastic development of sacral vertebral arches may play a role in the etiology of nocturnal enuresis. Further studies are warranted to investigate the natural history of children with enuresis with and without sacral dysplasia.