While children with imperforate or obviously mislocated anus are identified in the newborn period, some children with a very mild abnormality may escape identification until after the newborn period. This mild mislocation of the anus has been termed anterior ectopic anus.

Anterior ectopic anus is different from imperforate anus with perineal fistula in that the anal opening is usually of normal size, and only mildly misplaced. Most of these children come to medical attention due to severe constipation that is associated with the disorder. Surgery to relocate the anterior anus is simple, but does not change the fact that these children often have life-long problems with constipation independent of the actual anal location. Late diagnosis is often a source of frustration for families who feel that the constipation was due to failure to recognize the mislocated anus in the newborn period. Based on experience with other low anorectal abnormalities, the degree of constipation is independent of the age at diagnosis and correction.

Measurement of the anal position index is helpful. Anal position index is the ratio of anus-fourchette distance in girls and anus-scrotum distance in boys to the distance between coccyx and fourchette/scrotum.

Davari and Hosseinpour1 recommend the use of transparent adhesive tape placed longitudinally on midperinum in a way that it covers the anus. The fourchette/scrotum, anus center and the lower margin of coccyx are marked on it. Distances marked on each tape were then measured with the standard ruler.

Normal anal position index
Girls = 0.45 [+/-0.08 (95% CI: 0.44-0.46) ]
Boys = 0.54 [+/-0.07 (95% CI: 0.53-0.55)]

Mean +/-2 SD was considered as the normal range for an anus position.

They caution that the anal position index, however, can never be considered as the sole indication for the surgical intervention.

Anoplasty is a simple outpatient procedure that can be used to relocate the mild forms of anterior ectopic anus. More significant anterior displacement of the anus should be classified as imperforate anus with perineal fistula and treated with a standard transposition anoplasty or minimal Pena” procedure. Both methods require post-operative dilations for several months after the procedure and aggressive treatment of the associated constipation.

1. Davari HA, Hosseinpour M. Acta Paediatr. The anal position index: a simple method to define the normal position of the anus in neonate. 2006 Jul;95(7):877-80