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Imperforate Anus

Imperforate anus is a rare congenital abnormality in which anus is either present in an abnormal location or it is absent.


Presentation

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: 

  • Cardiovascular malformations are present in 12-22% of patients. The most common lesions reported are teralogy of Fallot and ventricular septal defects.
  • Tracheoesophageal abnormalities are present in 10% patients [4]
  • Lumbosacral defects, which afflict about one third of cases of imperforate anus, are most prevalent abnormalities [5] 
  • Spinal malformations, such as dysraphism, may increase in frequency with the degree of anorectal malformations; the most common type of dysraphism present is tethered spinal cord, which is reported in 35% of patients
  • In tethered spinal cord, instead of terminating between the first and second lumber vertebraes, the cord terminates in the lumber spine. 
  • Occurrence of lumbosacral spinal malformations in children adversely affect their prognosis with respect to fecal and urinary continence; cord lipomas and syringohydromyelia are common
  • Abnormalities of uterus and vagina are common. Uterus didelphys and bicornate uterus occur in 35% female patients
  • Vaginal agenesis and duplication have been reported; agenesis may have associated ipsilateral absence of ovary and kidney
  • About 50% girls, born with cloacal malformation, have the presence of a vaginal septum as a common abnormality 

In female children, examination is needed to find the presence of following malformations:

  • Presence of a perineal fistula as a small opening on the perineum
  • Search for presence of vestibular fistula by separating labia
  • Search for fourchette fistula at the junction of vestibule and perineum, characterized by anterior wet mucosa of vestibule and a posterior dry anoderm
  • Presence of cloaca, which is characterized by the presence of a single opening between shortened labia and the absence of fistula 
  • Presence of normal urethra and absence of vestibular fistula, such as in trisomy 21

Cases without perineal fistula require 24 hour observation for perineal fistula to open; it helps decide minimal anoplasty to treat instead of colostomy. 

Recurrent Urinary Tract Infection
  • In addition, this group also requires close follow-up of their kidneys to help mitigate the development of renal impairment by actively treating common problems such as recurrent urinary tract infections and reflux and by ensuring good bladder emptying[emedicine.com]
Wheelchair Bound
  • Ambulatory status in 62 patients of walking age revealed that 37 ambulated fully, 15 ambulated with devices, 2 ambulated minimally with devices and 8 were wheelchair bound. Continence data were available on 61 closed cases.[ncbi.nlm.nih.gov]
Leg Length Inequality
  • However, leg length inequality and recurrence of the deformities are not uncommon, necessitating further surgical interventions.[ncbi.nlm.nih.gov]
Primary Amenorrhea
  • An 18-year-old female presented with primary amenorrhea and progressive cyclic abdominal pain, which prompted emergency exploratory laparotomy.[ncbi.nlm.nih.gov]
  • These malformations can be discovered upon evaluation for urinary tract infection or primary amenorrhea. Pena A, Devries PA. Posterior sagittal anorectoplasty: important technical considerations and new applications.[emedicine.com]
Renal Insufficiency
  • Seven patients had associated malformations: one Hirschsprung's disease, one cloacal defect with renal insufficiency, three complex caudal malformations with tethered cord, one Down syndrome, and two psychological and psychomotor troubles.[ncbi.nlm.nih.gov]

Workup

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:

  • Urinalysis: It is necessary to detect rectourinary fistula in all cases where physical examination has not detected a single perineal orifice or fistula (perineal or vestibular) 
  • Abdominal ultrasonography: It is carried out before surgery to detect genitourinary abnormalities, abdominal masses and hydronephrosis. It needs to be repeated after 72 hours because early findings may not be able to detect hydronephrosis caused by vesicoureteral reflux
  • Spinal ultrasonography or MRI: It is required in all cases of anorectal malformations, minor or major, to detect spinal defects 
  • Lateral pelvic radiography: The technique employs a radiomarker on anal dimple and the child is placed in a prone position with the hips slightly raised. It is carried out 24 hours after birth, when maximum pelvic pouch distention has occurred. It is used as an alternative to lateral radiography (invertography), which is carried out by holding baby upside down, to observe gas level in distal rectum
  • Sacral radiography: Posteroanterior and lateral views of sacrum are taken to determine sacral ratios and detect defects, like presacral masses and hemivertebrae 
  • Augmented-pressure distal colostography: The test is required before colostomy to clarify anatomy in all children having malformations. The test is useful in detecting fistulas of colon or urinary tract 

Imperforate anus cases require a thorough examination of lower spine, abdomen, rectum and genitals [6]. 

Treatment

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:

  • Newborn with imperforate anus should not be fed and administered intravenous hydration
  • In cases with suspected urinary fistula, broad-spectrum antibiotics may be administered; anaerobic coverage may follow only after 48 hours of life
  • Cardiac murmurs detected during physical examination may be evaluated before surgical intervention 
  • One or more surgical procedures may follow depending upon the complexity of the case as revealed by physical examination and imaging studies

Surgical procedures used for treatment of anorectal malformations are:

  • In cases with perineal fistulas or no fistulas, surgeon may follow primary pull-through approach and proceed without colostomy and close rectal pouches (<1 cm). Same procedure may follow in male child and female child with vestibular fistulas 
  • Neonatal colostomy is performed in cases who are not manageable through primary pull-through approach due to complexity of the case, due to urinary fistulas in male child and vestibular fistula or cloaca in female child, no fistula cases in both sexes in >1 cm from perineal skin and cases with associated malformations 
  • Posterior sagittal pull-through with colostomy approach is used in male child with rectourinary fistulas, such as bladder-neck and prostatic  fistulas, in female child with vestibular fistula or cloaca and in patients of both sexes which do not have fistula under the condition of rectal pouch presence beyond 1 cm, revealed through 24-hour lateral prone abdominal radiography
  • Colostomy closure is performed by traditional surgical procedure, after the neoanus has achieved the desired size and complete healing has been achieved.

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 [7]. Dietary management of constipation includes avoidance of foods that cause constipation and use of high fiber and laxative foods.  

Prognosis

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 [3]. 

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.

Etiology

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. 

Epidemiology

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 [2]. 

Sex distribution
Age distribution

Pathophysiology

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. 

Prevention

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.

Summary

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 [1]. 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. 

Patient Information

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: 

  • Anus is absent or it is narrowed due to stenosis
  • The rectum may not be connected to colon 
  • The rectum may not open in anus. Instead, it may open in a pouch, urethra, bladder, penis, scrotum or vagina  
  • Associated malformations involving genitals, urinary system and spine

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 new born does not pass stool within 24-48 hours after birth
  • The newborn develops swollen belly
  • Stool may pass through abnormal routes of the involved parts of the genitourinary systems like urethra, vagina, penis or vagina

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. 

Post-operatively, constipation is a major problem. It can be managed by providing a fibrous diet, stool softeners, laxatives, enemas  and by practicing a bowel program.

References

Article

  1. Pena A, Devries PA. Posterior sagittal anorectoplasty: important technical considerations and new applications. J Pediatr Surg. 1982; 17(6):796-811.
  2. Beudeker N, Broadis E, Borgstein E, Heij HA. The hidden mortality of imperforate anus. Afr J Paediatr Surg. 2013;10(4):302-6.
  3. Pena A. Anorectal malformations. Semin Pediatr Surg. 1995; 4(1):35-47.
  4. Rosenbaum DG, Kasdorf E, Renjen P, Brill P, Kovanlikaya A. Sling left pulmonary artery with patent type IIA tracheobronchial anomaly and imperforate anus. Clin Imaging. 2014; 38(5):743-6.
  5. Stathopoulos E, Muehlethaler V, Rais M, et al. Preoperative assessment of neurovesical function in children with anorectal malformation: association with vertebral and spinal malformations. J Urol. 2012; 188(3):943-7. 
  6. Mirza B, Ijaz L, Saleem M, Sharif M, Sheikh A. Anorectal malformations in neonates. Afr J Paediatr Surg. 2011; 8(2):151-4.
  7. Bischoff A, Levitt MA, Bauer C, Jackson L, Holder M, Pena A. Bowel management for fecal incontinence in patients with anorectal malformations. J Pediatr Surg. 2009; 44(6):1278-83.

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Last updated: 2019-06-28 12:05