Very early in development, the urinary tract, rectum, and anus are all part of the same structure. They separate by the seventh week of gestation. At the time of separation, the urinary tract already has an opening on the skin, but the anus is covered by a thin membrane. By eight weeks of gestation, the anal opening typically appears.
Anal stenosis refers to a narrowing of the anal opening, which makes it difficult for stool contents to pass through easily.
Some children are born with no anal opening at all. This is called an imperforate anus. The rectum ends in a blind pouch, about 2 cm inside the perianal skin. Usually the sphincters are well developed.
The most frequent anorectal defect seen in boys is the recto-urethral fistula, or an open connection between the rectum and the lower part of the urethra.
The rectovesical fistula is an open connection between the rectum and the bladder.
These malformations are rare, occurring in about 1 in 4000 babies. Sometimes anorectal malformations are present along with anomalies of the spine, heart, trachea, esophagus, kidneys, and/or limbs.
Children with anal stenosis can be particularly colicky babies, because of the discomfort associated with the stool backing up.
The stool may exit under pressure and look almost like a squirt gun.
Those with imperforate anus may also be fussy – but they pass no stool at all through the anus.
Those with fistulas might be seen to have particles of meconium or stool in the urine.
The diagnosis may be suspected by the history and physical exam, but imaging studies are often necessary to determine the extent of the problem.
Treatment of anal stenosis usually involves gentle dilation of the anal opening. This is typically done twice a day. Every week a slightly larger lubricated dilator is passed to stretch the anus until it reaches normal size. In very mild cases, softening the stool may be enough until the anus grows sufficiently. Suppositories can make the child comfortable in the short run, but do have the risk of developing dependence. At around 4 months, apple or even prune juice may help the child pass stool. Rarely, surgery is needed to ensure an opening of adequate caliber. If this is an isolated anomaly, the prognosis is excellent.
For children with imperforate anus, a colostomy is often needed during the newborn period, but once the final surgery corrects the defect, the prognosis is likewise excellent.
Children with recto-urethral fistulas also require a colostomy before the definitive repair period. The long-term prognosis for normal urethral and rectal function is good.
Children with rectovesical fistulas usually also have poorly developed sacral bones and anal sphincters.
For all anorectal malformations there is a very good correlation between the degree of development of the sacral bone with the final bowel and bladder functioning after correction. Children with an absent sacrum will almost certainly have permanent incontinence. Those with a well-developed sacrum will generally have an excellent outcome.
Prevention is not generally effective.
Anal stenosis, Imperforate anus, Recto-urethral fistula, Rectovesical fistula.