Imperforate anus (IA) is a congenital abnormality in which the bowel fails to perforate or only partially perforates the pelvic muscular floor.
IA may also perforate the epidermal covering of the pelvic muscular floor (anal membrane).
Spectrum of anorectal malformations that range in severity from imperforate anal membrane to complete caudal regression
IA has been classically described as low and high anomalies.
In a low lesion, the colon remains close to the skin and there may be a stenosis of the anus, or the anus may be missing altogether, with the rectum ending in a blind pouch.
In a high lesion, the colon is higher up in the pelvis, with a fistula connecting the rectum and the bladder, urethra, or the vagina.
More recently, classification of IA is by type of associated fistula: rectal, bladder, urethra, or vaginal.
Epidemiology
Prevalence is estimated to be in the range of 1:3,000-1:5,000.
High lesions are more common in males (2:1).
Low lesions occur with equal frequency in both sexes.
Risk Factors
Genetics
Can be an isolated defect or part of a syndrome or association
Syndromic disorders that contain IA are associated with defects on chromosomes 6, 7, 10, and 16.
Can be associated with trisomy 21 (typically IA without fistula)
Can be part of omphalocele-exstrophy of the bladder-IA-spinal defects (OEIS) complex or cloacal exstrophy (EC)
Pathophysiology
During the 6th week of fetal development, the hindgut comes into contact with the cloacal membrane. The hindgut is divided into a ventral urogenital and dorsal rectal component. By the 8th week, the dorsal 1/2 perforates to the exterior. In IA, the process is arrested during this critical period.
There is a wide spectrum of anatomic variants of IA; commonly associated with urologic and spinal defects
Classification of anatomic variants is based on the relationship between the rectum and the puborectalis muscle: supralevator (high) and translevator (low) malformations
Cloaca is a complex defect, where the rectum, urethra, and the vagina drain into a common channel that communicates with the perineum.
A fistula communicating from the rectum to the external opening (perineal fistula) or to the urogenital system is present in 90% of cases.
Females: Most common defect is a recto-vestibular fistula where the rectum opens into the vestibule.
Males: Most common defect is a rectourethral fistula from the rectum to lower posterior urethra (bulbar) or upper posterior urethra (prostatic).
Commonly Associated Conditions
Other anomalies are present up to 50% of patients with an IA.
IA can be associated with vertebral, cardiac, tracheoesophageal fistula, renal, and limb anomalies (VATER or VACTERL).
Most children are diagnosed during a routine neonatal examination.
Failure to pass meconium, a history of constipation, and signs of low intestinal obstruction (abdominal distention and vomiting) should mandate reexam of perianal area.
Approximately 13-25% may present beyond the neonatal period and have higher morbidity (19-35%) and mortality (4-10%).
Physical Exam
Placement of the anus: lack of or anterior/lateral malposition
Decreased or abnormal radial corrugations of the anus
Abnormal rectal caliber
Poor anal tone or patulous anal opening
Absent or asymmetric anal wink
Spinal dimples or tufts
Flat buttocks, abnormal gluteal crease, lack of midline grove
Abnormal genitourinary or neurologic examination
Associated renal, cardiac, vertebral, or limb anomalies.
Diagnostic Tests & Interpretation
Exclusion of associated anomalies
Classification of the malformation (established after 18-24 hours)
Imaging
Prone cross-table lateral and invertogram: After sufficient time for a transit of gas (>12 hours after birth), the child is placed in an upside-down position for 5 minutes, after which a lateral view of the pelvis is obtained to identify level of obstruction.
Lumbosacral films to evaluate for vertebral anomalies and sacral integrity
MRI of the spine and pelvis should be considered to look for a tethered cord and evaluate the pelvic anatomy.
Water contrast enema to evaluate the anatomy: rectosigmoid caliber and genitourinary fistulas
Renal and pelvic ultrasound to evaluate for hydronephrosis, megaureters, and hydrocolpos
Voiding cystoureterogram and IV pyelogram can be used if urinary tract anomalies are highly suspected.
Echocardiogram
Differential Diagnosis
No disorders can mimic IA.
Task is to define the location of the termination of the bowel and the opening of the fistula.
Treatment
Surgery/Other Procedures
Surgery should be performed by an experienced surgeon.
High lesions require an emergent and protective diverting colostomy, followed by pull-through procedure with posterior sagittal anorectoplasty (PSARP) at 3-9 months of age. Colostomy is closed after the anoplasty has healed and any necessary secondary dilations have been completed.
Laparoscopy-assisted PSARP in conjunction with muscle electrostimulation may be performed in those with complex and high lesions.
Transanal anorectoplasty was recently shown to have sphincter sparing and results in accurate placement of anus in external canal with good neurologic function.
After surgery, follow-up with anal dilatation helps minimize the risk of stricture formation and helps the newly constructed canal to become functional.
Complications of surgery include stricture of the anocutaneous anastomosis, rectourinary fistula, mucosal prolapse, constipation, and incontinence.
Ongoing Care
Patient Education
Prognosis for bowel and urine continence depends on type of malformation and sacral integrity.
Low malformations have greater bowel control, increased incidence of megacolon with subsequent constipation, and "overflow"� incontinence.
High malformations have increased associated defects and poor bowel and urinary control.
Prognosis
Prognostic factors: type of malformation, sacral integrity, and length of the cloaca common channel
Sacral integrity is the most important prognostic indicator of bowel control.
Good prognostic indicators of bowel control:
Normal sacral integrity
No presacral mass
Two well-formed buttocks and midline grove
Low anorectal malformations (rectal atresia, rectoperineal fistula, rectobulbar urethral fistula, cloaca with common channel <3 cm, and IA without fistula)
Poor prognostic indicators of bowel control:
Abnormal sacral integrity
Myelomeningocele
High anorectal malformations (rectoprostatic urethral fistula, rectobladder neck fistula, cloacal exstrophy cloaca, >3 cm common channel, complex defects)
Experienced centers report
~75% have voluntary bowel movements after age 3 years, of which 50% continue to have intermittent fecal incontinence.
In their cohort, ~25% have fecal incontinence despite treatment.
Continence can be attained in 80-90% of patients who have low lesions.
<50% of patients with high lesions are continent before school age, but most continue to improve and achieve continence by adolescence.
Many patients will need regular enemas or comprehensive bowel management program for years to prevent or reduce constipation and fecal incontinence.
Additional Reading
Arbell �D, Gross �E, Orkin �B. Imperforate anus, malrotation, and Hirschsprung's disease: a rare and important association. J Pediatr Surg. 2006;41(7):1335-1337. �[View Abstract]
Chen �CJ. The treatment of imperforate anus: experience with 108 patients. J Pediatr Surg. 1999;34(11):1728-1732. �[View Abstract]
Di Lorenzo �C, Benninga �MA. Pathophysiology of pediatric fecal incontinence. Gastroenterology. 2004;126(1)(Suppl 1):S33-S40. �[View Abstract]
Javid �PJ, Barnhart �DC, Hirschl �RB, et al. Immediate and long-term results of surgical management of low imperforate anus in girls. J Pediatr Surg. 1998;33(2):198-203. �[View Abstract]
Keppler-Noreuil �K, Gorton �S, Foo �F, et al. Prenatal ascertainment of OEIS complex/cloacal exstrophy-15 new cases and literature review. Am J Med Genet A. 2007;143A(18):2122-2128. �[View Abstract]
Levitt �M, Kant �A, Pe �a �A. The morbidity of constipation in patients with anorectal malformations. J Pediatr Surg. 2010;45(6):1228-1233. �[View Abstract]
Levitt �M, Pe �a �A. Update on pediatric faecal incontinence. Eur J Pediatr Surg. 2009;19(1):1-9. �[View Abstract]
Lima �M, Tursini �S, Ruggeri �G, et al. Laparoscopically assisted anorectal pull-through for high imperforate anus: three years' experience. J Lapoaroendos Adv Surg Tech A. 2006;16(1):63-66. �[View Abstract]
Pakarinen �M, Rintala �R. Management and outcome of low anorectal malformations. Pediatr Surg Int. 2010;26(11):1057-1063. �[View Abstract]
Pena �A, Hong �A. Advances in the management of anorectal malformations. Am J Surg. 2000;180(5):370-376. �[View Abstract]
751.2 Atresia and stenosis of large intestine, rectum, and anal canal
565.1 Anal fistula
ICD10
Q42.3 Congenital absence, atresia and stenosis of anus without fistula
Q42.2 Congenital absence, atresia and stenosis of anus with fistula
SNOMED
204731006 Imperforate anus (disorder)
204716002 Atresia of anus with fistula (disorder)
FAQ
Q: Is IA an isolated defect in my child?
A: IA is often associated with multiple other anomalies. In particular, renal and vertebral anomalies must be excluded.
Q: What is the genetic basis for this defect?
A: IA can be associated with chromosomal anomalies or can be an isolated problem.
Q: How likely is it that my child will ever be able to be toilet trained successfully?
A: Successful toilet training will depend on what type of IA defect your child has: Children with high lesions may have more difficulty becoming toilet trained than children with low lesions. All children should improve over time but will need specialist treatment and a comprehensive bowel management program for many years to prevent or reduce constipation and fecal incontinence.