A congenital abnormality characterized by the persistence of the anal membrane, resulting in a thin membrane covering the normal ANAL CANAL. Imperforation is not always complete and is treated by surgery in infancy. This defect is often associated with NEURAL TUBE DEFECTS; MENTAL RETARDATION; and DOWN SYNDROME.

Synonyms: Atresia, Anal, Atresias, Anal, Anal Atresias, Imperforate Anus, Anal Atresia, Anus, Imperforate