Imperforate anus is a rare congenital abnormality in which anus is either present in an abnormal location or it is absent.
Presentation of cases may vary widely. While prenatal ultrasonography findings may appear normal, presence of polyhydramnios or intra-abdominal cysts are suggestive of imperforate anus along with hydrocolpos or hydronephrosois. Examination of perineum may reveal fistulas with meconium running into scrotal raphe or existence of a bucket-handle malformation in anal dimple. When there is no anal opening, urine is examined and child is observed for 24 hours.
Imperforate anus is found in association with malformations of tracheoesophageal, gastrointestinal, lumbosacral and urogenital systems:
In female children, examination is needed to find the presence of following malformations:
Cases without perineal fistula require 24 hour observation for perineal fistula to open; it helps decide minimal anoplasty to treat instead of colostomy.
In newborn babies, imperforate anus may be identified at the first physical examination. If missed, the diagnosis can be made on subsequent examination, within the next 24 hours, when abdomen is distended or there is failure to pass meconium. If imperforate anus is doubted and physical examination does not reveal imperforate anus, the following tests may be carried out:
Imperforate anus cases require a thorough examination of lower spine, abdomen, rectum and genitals .
Treatment depends upon the nature of anorectal malformations, associated malformations and the seriousness of the individual case. Life-threatening conditions are treated on priority. Treatment involves individual assessment of the case and systematic followup:
Surgical procedures used for treatment of anorectal malformations are:
Constipation or anal incontinence is the most common complication of post-operative repair of imperforate anus. Constipation can be controlled by diet, laxatives, enemas and medications . Dietary management of constipation includes avoidance of foods that cause constipation and use of high fiber and laxative foods.
Patients with anorectal malformations, who do not have significant life-threatening comorbidities, should survive normally. In general, prognosis is based on the probability of primary fecal continence.
Continence is defined as voluntary bowel movement with minimal 'soiling' or 'fecal incontinence'. It varies from patient to patient depending upon the primary and associated malformations. Voluntary bowel movements can be found in several types of abnormalities: in 90% of girls having vestibular fistula, in 80% boys with bulbular urethral fistula, in 66% of boys with prostatic urethral fistula, and in 15% boys with bladder-neck fistulas .
Serious associated malformations such as tethered spinal cord, hemivertebrae or spinal dysraphism increase the risks of fecal incontinence. However, most defects can be corrected by surgery. Wherever complex surgeries are involved it is still possible to control bowel movements, but constipation may remain a problem. A bowel management program can be followed by using high fiber diet, by using stool softners and also occasional enemas.
The exact cause and mechanism of imperforate anus or anorectal abnormalities is not known. The abnormality is caused during embryonic development. Formation of cloacal membrane and its subsequent breakdown into urogenital and anal openings is normally completed by the 8th week of gestation. Abnormalities associated with imperforate anus are caused when there arise defects in the formation and shape of the posterior urorectal septum. Development of Müllerian ducts appears after this period. The reason for their incorporation in anorectal malformations is therefore not understood.
Most cases of imperforate anus are sporadic in nature. This possibly explains that there is no known cause or associated risk factor which could possibly cause this abnormality. Families having a history of children born with this malformation may be considered to have a genetic link.
Incidence of imperforate anus is reported to be about 1 in 5000 live births. The abnormality is more common in boys as compared to girls, and it is more prevalent in Asians. In female babies with imperforate anus, the rectum, bladder and vagina may typically open in a large common opening called cloaca. The situation arising as a result of imperforate anus is as such not fatal. However, when present along with cardiac and renal abnormalities, the condition could be life threatening.
Morbidity caused by imperforate anus is of two types: malformation-related and malformation-associated. In the first category fall those malformations which are related to rectal motility, innervation of anorectal region, and musculature of the anal sphincter. The most common morbidity related to this type of abnormality is constipation. When the abnormality is mild in nature, constipation may not be diagnosed for a long time. Untreated constipation may, in turn, cause rectal dilation leading to complications such as fecal impaction and encopresis.
Malformation-associated morbidity commonly leads to fecal and urinary incontinence. Serious malformations such as bladder-neck fistulas, formation of cloaca due to joining of the openings of bladder, rectum and vagina, malformations of prostate, and deficient innervation and musculature lead to increased possibilities of fecal and urinary incontinence. Abnormalities affecting urinary sphincters or the bladder neck, caused by joining of bladder neck with rectum or vagina, lead to inability to void urine completely or urinary incontinence. Corrective surgery to resolve malformations may , however, be followed by instances of perforations or septic conditions, leading to serious morbidity and even death .
Abnormal development processes in embryogenesis are at the root cause of pathophysiological changes observed in patients born with imperforate anus. However, the precise abnormal steps causing these abnormalities during embryogenesis are not known.
It is believed that the rectum and anus develop from the dorsal side of the hindgut or cloacal cavity. At this time, lateral ingrowths arise from the mesenchyme to form urorectal septum in the midline. The septum plays the role of separating bladder and urethra dorsally from rectum and anal canal. While the urorectal septum closes the duct by 7th week of gestation, the ventral urogenital system forms an external opening; the anus is formed later by fusion of anal tubercles and external called proctodeum. The proctodeum deepens further towards the rectum but the two structures are separated by the anal membrane. By the 8th week of gestation this membrane disintegrates and joins the anus and rectum.
Depending upon the ebryonic stage, at which the developmental process is affected, the outcome of anorectal abnormalities varies. Different variations in anorectal malformations can exist in the form of anal stenosis, incomplete anal membrane rupture, anal agenesis, failure of cloaca to descend, and failure of proctodeum to invaginate. Continued communication between urogenital tract and rectal portions causes rectourethral / rectovestibular fistulas.
Imperforate anus is usually accompanied by the external anal sphincter, which is derived from exterior mesoderm, but the level of its formation may vary greatly. The sphincter may have robust muscles such as in case of perineal and vestibular fistulas or no muscle, as in cases of long-common-channel cloaca, bladder-neck and prostate fistulas.
Imperforate anus being a congenital malformation, it cannot be prevented as such. However, the morbidity and mortality associated with the malformation can be largely prevented by adequate surgical intervention and management of fecal and urinary incontinence. Parents having a history of several cases of imperforate anus in close family are advised genetic counselling.
Imperforate anus is part of a broader class of inborn malformations involving intestinal tract, urogenital system and lower spine. The condition imperforate anus is diagnosed when the new born either do not have the anus at the designated place or it is totally absent. The condition also involves abnormality in muscles and nerves associated with anus.
In this condition, the involved malformations can be deep-seated in the pelvis region and may not be easy to visualize through incisions made in the abdomen. Traditional surgeons also did not consider division of the posterior midline as appropriate because they believed that such incisions caused greater risk to continence. Following the use of a traditional sacral incision and making it of progressively larger size by Pena et al in 1982, the group adequately visualized the anatomy of malformations . Designated as posterior sagittal anorectoplasty (PSARP) or posterior sagittal anorectovaginourethroplasty (PSARVUP), the technique allowed opening of the entire posterior sagittal plane with a detailed view of malformations. This allowed adequate reconstructive procedures to treat affected children.
Reconstructive surgery is however no assurance for complete recovery and normal continence and bowel functions. Poorly developed nerves and muscles found in association with imperforate anus may not be repaired completely by surgery. If primary urinary and fecal continence is not achieved, suitable bowel management regimes need to be adopted in all such cases for improvement in the quality of life of such patients.
Imperforate anus is a rare born defect and is the result of defects in the process of fetal development. The condition is found in association with several birth defects. The condition is characterized by the absence of anus and malformations associated with its development, such as:
Imperforate anus can be detected by general physical examination at birth. Associated defects can be detected following various common and specialized tests. Common symptoms associated with imperforate anus are:
The condition can be life-threatening or manageable. Surgical procedures can correct the abnormalities to a great extent in cases of mild nature. In complicated cases in which multiple organs are involved, the associated organs will also need to be repaired. Colostomy will be needed in some cases to connect the rectum directly to the abdomen; this allows collection of feces in a pouch.