Anal endosonography has recently been popularized in adult patients in order to access staging of rectal cancer and other lesions of the anorectum. This study is not familiar to pediatric surgeons. We performed anal endosonography in 30 children without anorectal disease in order to determine the standard morphology of the anorectum. The internal anal sphincter(IAS) was clearly identified as a homogeneous hypoechoic circular band, extending caudally to a level just proximal to the anal verge. The external anal sphincter(EAS) showed mixed echogenicity and different architecture along the anal canal; the EAS was U-shape in the upper canal and it had a circular pattern in the lower canal. In the upper canal of girls, the perineal body and the vagina were found just anterior of the anal canal, which made the U shape of the EAS. In the male, the sphincter tapered anteriorly into two arcs that met in the midline. The perineal body was prominent in the female. Posteriorly, the anococcygeal ligament was represented by a triangular shadow in both sex. The thickness of the lAS was measured in 3 directions, left, right and posterior, at 3 levels, upper, middle and lower areas of the anal canal. The average thickness was 0.86-2.40 mm between 6 and 18 months of age(Group 1), 0.88-3.20 mm between 19 and 36(Group 2), 1.07-2.20 mm between 37 and 54(Group 3) and 1.18-2.42 mm more than 54-month-old(Group 4). The thickness was correlated wtih the age of the children only in the right upper(p= 0.008) and the left middle portion(p=0.015). We were able to obtain standard morphologic features of the normal anal canal in children with anal endosonography. We believe that this technique is a safe and an effective procedure to evaluate anorectal lesions in children.
