A congenital abnormality in which the anorectal region is abnormal or incompletely developed. In some cases, the rectum may end and not connect with the anus, or it may connect in the wrong spot. For example, it may connect to the urethra, bladder, or vagina. In other cases, the anus may be very narrow or missing altogether. The result is that stool cannot pass out of the colon. Imperforate anus occurs in about 1 in 5,000 infants.