Magnetic resonance imaging measurement of the anorectal striated muscle complex in normal children

PurposeThe aim of the study was to describe and establish a normal measurement of the striated muscle complex (SMC) in healthy children using body phased-array or head coil magnetic resonance imaging.MethodsImaging was performed in 20 boys and 20 girls (age range, from 3 months to 14 years; average age, 3.2 years) without anorectal disorders. The dimensions of the puborectalis muscle (PR) and external anal sphincter (EAS) were measured in different planes.ResultsThere was a close positive correlation between absolute width and length of SMC and age (P < .05), whereas there was no correlation between the relative width and length of SMC and age (P > .05). Normal relative length of the PR and EAS were measured as 0.47 ± 0.04 and 0.41 ± 0.04, respectively, and the normal relative width of PR and posterior EAS were 0.50 ± 0.04 and 0.44 ± 0.04 in children younger than 14 years.ConclusionsThe width and length of PR and EAS increase progressively with age. The relative width and length of PR and EAS were not variable with age. A relative width and length of PR and EAS were chosen as objective criteria for normal SMC in children younger than 14 years.