Shape and volume of internal anal sphincter showed by three-dimensional anorectal ultrasonography

Abstract Purpose The aim of this work is to characterize the shape and the volume of the internal anal sphincter (IAS) in normal subjects by three-dimensional anorectal ultrasonography. Methods Thirty-nine normal volunteer males (mean age 58.5 ± 18.7) and 25 females (mean age 59.4 ± 14.1) were submitted to anorectal ultrasonography. The tissue is defined by a semiautomatic procedure. Measurements of thickness, length and volume were assessed automatically. The software provides an average number of 57,600 thickness measurements, 360 length measurements for each zone (90 for each quadrant) and seven volume measurements (one for each anatomical area).The mean values of magnitudes were calculated for the entire volume in each quadrant and zone. Age and gender-related variations were analyzed. Results In assessments of the whole tissue, only thickness was gender-related, with greater thickness for females (male thickness: 1.81 ± 0.47 mm, female thickness 2.16 ± 0.57 mm, P -value  P -value  P -value  3 vs 2169 ± 871 mm 3 , P -value  P -value  P -value  The male population was significantly positively correlated with ageing for volume in the whole tissue ( ρ  = 0.32, P -value  ρ  = 0.33, P -value  ρ  = 0.39, P -value  Conclusion This new method is useful to understand both functional anal disorders and local damage which may affect only part of the muscle tissue.