Imperforate anus is a congenital absence or obstruction of the anal opening. Imperforate anus is a malformation of the anorectal region that may occur in several forms. The rectum may end in a blind pouch that does not connect with the colon. Or, it may have openings to the urethra, bladder, base of penis or scrotum in boys, or vagina in girls. A condition of stenosis
(narrowing) of the anus or absence of the anus may be present.
There is no known cause for the condition which runs equally through all racial, social, cultural and economic groups. One thing is known: Parents should never blame themselves for the condition. There is no evidence to suggest it is caused by something done as an adolescent, on the night of conception or during the pregnancy. The complex miracle of reproduction sometimes just goes astray. The anus and rectum develop from the dorsal potion of the hindgut or cloacal cavity when lateral ingrowth of the mesenchyme forms the urorectal septum in the midline. This septum separates the rectum and anal canal dorsally from the bladder and urethra. The cloacal duct is a small communication between the 2 portions of the hindgut; downgrowth of the urorectal septum closes this duct by the seventh week of gestation. During this time, the ventral urogenital portion acquires an external opening; the dorsal anal membrane opens later. The anus develops by a fusion of the anal tubercles and an external invagination, known as the proctodeum, which deepens toward the rectum but is separated from it by the anal membrane. This separating membrane should disintegrate during the eighth week of gestation.
The malformations are caused by abnormal development of the fetus, and many are associated with other birth defects. Imperforate anus is a relatively common congenital malformation that occurs in about 1 out of 5,000 infants.
In the newborn period, IV fluid therapy is required until enteral continuity can be established. After defining the type of anomaly, maintain enteral decompression with an orogastric sump drain. Broad-spectrum antibiotics generally are administered to prevent urinary infection from a presumed rectourinary fistula. Search for associated anomalies during this period because their presence and severity may affect surgical planning.
A colonic diversion is recommended for patients with high lesions until later definitive repair can be achieved. Although a loop colostomy is easily performed, a completely diverting type of colostomy is preferred to prevent continued contamination of the urinary system. Surgical care of infants with imperforate anus has been greatly influenced by the study and practice of Alberto Pena, whose posterior sagittal approach to surgical correction of imperforate anus has been adopted by most pediatric surgeons. Essentially, this approach from the midline posterior sagittal plane identifies the individual components of the muscle complex and end portion of the rectum. The fistulous connection to the genitourinary tract usually can be identified and corrected in a similar manner. Electrical stimulation of the external anal sphincters and levator muscle complex is mandatory for proper reconstruction.
Cloacal anomalies involve special challenges for the surgeon. Dissection and definition of the individual components of the urogenital sinus are critically important. Proper repair requires advancing the urethra and the vagina to the perineum and the rectum. Some patients require a combined abdominal and perineal approach to reconstruct these complex lesions. Low lesions can be addressed with a limited posterior sagittal approach or similar operation to transpose the anus to the area of the external anal sphincters.