Mid-anal sphincteric malformation, cause of constipation in anterior perineal anus.

Constipation characterized by straining at defecation has been reported in association with an anteriorly located, but otherwise "normal' anus, however its cause is not known. In this communication the pathogenesis of constipation has been discussed on the basis of clinical features and intraoperative findings seen in seven children with this syndrome. The primary cause of constipation lies in the congenital malformation of the mid-portion of the external sphincter and weakness of the corresponding segment of the anal canal.