Low muscle volume of the anal sphincter complex:A novel prognostic factor in children with anorectal malformations?

Abstract Background/Purpose The anal sphincter complex (ASC) plays a key-role in continence and is often dysfunctional in infants born with anorectal malformations (ARM). The ASC is well depicted by magnetic resonance (MR) imaging but volumetric reference data are lacking in infants. Thus, we tested the feasibility of MR-based ASC volumetry, collected reference data, and compared them with cases of favourable prognosis and unfavourable prognosis (as defined by the type of ARM). Methods We determined ASC volume on T2-weighted MR-images of seventy-six infants (ARM n = 33; controls n = 43) by manual segmentation. Inter-operator agreement was assessed by intraclass-correlation coefficient. Linear regression was used to establish weight-dependent reference data. Observed-to-expected ASC volumes of patients with unfavourable and favourable prognosis were compared (unpaired t-test). Results ASC volumetry was feasible in all cases. Patients with ARM had low ‘observed-to-expected’ ASC volume (-18.1%; p = 0.006). ‘Observed-to-expected’ ASC volume differed significantly between patients with favourable and unfavourable prognosis (p Conclusion We confirmed the feasibility of MRI-based ASC volumetry and provided initial reference data for infants. Although ASC volumes were lowest in infants with ARM of unfavourable prognosis for fecal continence, the value of ASC volume as prognostic parameter remains to be determined.