Incidence of anterior displacement of the anus and its relationship to constipation in children.

Anterior displacement of the anus (ADA), otherwise known as "anterior ectopic anus," is considered to be a common congenital abnormality of anorectal region. However, the true incidence of this condition is not well known. We evaluated the incidence of ADA and its relationship to constipation in 357 children (191 boys and 166 girls) who were admitted to our hospital with unrelated disorders. For this purpose, the anal index was defined as the ratio of the scroto-anal distance to the scroto-coccygeal distance in boys, and as the ratio of the fourchette-anal distance to the fourchette-coccygeal distance in girls. An anal index of less than 0.34 in girls and less than 0.46 in boys was determined to be an ADA. The incidence of ADA was 43.4% in girls and 24.6% in boys (P < 0.01). However, the incidence of constipation in children with a normal anal index and those with a low anal index indicative of an ADA was not significantly different. These findings suggest that ADA is a common variant of the normal anatomical location of the anus, especially in girls.