Pediatric Imperforate Anus 

  • Author: Nelson G Rosen, MD, FACS, FAAP; Chief Editor: Carmen Cuffari, MD   more...
 
Updated: Jan 25, 2010
 

Background

Anorectal malformations include a wide spectrum of defects in the development of the lowest portion of the intestinal and urogenital tracts. Many children with these malformations are said to have an imperforate anus because they have no opening where the anus should be. Although the term may accurately describe a child's outward appearance, it often belies the true complexity of the malformation beneath. When a malformation of the anus is present, the muscles and nerves associated with the anus often have a similar degree of malformation. The spine and urogenital tract may also be involved.

The position and nature of these malformations made repair difficult for early surgeons. The affected organs are located deep in the pelvis and are not well visualized through abdominal incisions. Traditional surgical dictum did not allow for division of the posterior midline because this division of the muscle was believed, somewhat erroneously, to cause incontinence in the child. Therefore, surgeons approached these malformations using a combined abdominal, sacral, and perineal approach, with limited visibility. Such approaches have put continence, and surrounding genitourinary structures, at greater risk than simply cutting sphincter muscles because of the difficulty of adequately visualizing the malformation through limited incisions. This principle was central to the development of the surgical techniques currently used to repair these malformations.

In 1982, Peña et al reported the results of the use of a posterior sagittal surgical repair approach.[1] Peña et al used the traditional approach with a sacral incision and made the incisions progressively larger in an attempt to adequately visualize the anatomy. Eventually, the entire posterior sagittal plane was opened, affording a full view of the complete malformation. This technique, referred to as posterior sagittal anorectoplasty (PSARP) or posterior sagittal anorectovaginourethroplasty (PSARVUP), has led to a more complete understanding of the anatomy of these children and of what is required to repair the malformations with optimal results.

After reconstructive surgery for the malformation, many children still experience effects in the form of urinary or fecal incontinence. Despite optimal surgical management, no adequate repair for poorly developed muscles or nerves has been developed. Bowel-management regimens can provide an excellent quality of life for these children when primary continence is not achievable.

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Pathophysiology

The embryogenesis of these malformations remains unclear. The rectum and anus are believed to 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 is believed to close this duct by 7 weeks' 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 at 8 weeks' gestation.

Interference with anorectal structure development at varying stages leads to various anomalies, ranging from anal stenosis, incomplete rupture of the anal membrane, or anal agenesis to complete failure of the upper portion of the cloaca to descend and failure of the proctodeum to invaginate. Continued communication between the urogenital tract and rectal portions of the cloacal plate causes rectourethral fistulas or rectovestibular fistulas.

The external anal sphincter, derived from exterior mesoderm, is usually present but has varying degrees of formation, ranging from robust muscle (perineal or vestibular fistula) to virtually no muscle (complex long–common-channel cloaca, prostatic or bladder-neck fistula).

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Epidemiology

Frequency

United States

Anorectal malformations occur in approximately 1 newborn per 5000 live births.

Mortality/Morbidity

Anorectal and urogenital malformations are rarely fatal, although some associated anomalies (cardiac, renal) can be life threatening. Intestinal perforation or postoperative septic complications in a newborn with imperforate anus can result in mortality or severe morbidity.

Morbidity generally arises from the following 2 sources:

  • Malformation-related morbidity
    • Malformation-related morbidity relates to associated malformations of rectal motility, anorectal innervation, and sphincteric musculature. The most common morbidity in this category is constipation. Most children have mild malformations that commonly result in constipation for reasons that remain unclear. If left untreated, chronic constipation results in rectal dilation, which worsens the constipation. This becomes a vicious cycle, which, if untreated, results in fecal impaction and overflow pseudoincontinence, also known as encopresis.
    • The most severe forms of malformation-associated morbidity are fecal and urinary incontinence. Higher malformations, such as long–common-channel cloacae and prostatic or bladder-neck fistulas, are associated with poorer nerve and muscle formation, all of which increase the likelihood of fecal or urinary incontinence. Malformations that directly involve urinary sphincteric mechanisms, and, specifically, any malformation in which the rectum or vagina joins the urinary tract at the bladder neck, often results in either urinary incontinence or inability to completely void.
  • Surgery-related morbidity
    • This can include standard complications such as line infections and pneumonia.
    • Wound infections or anastomotic breakdowns can occur in any intestinal surgery.
    • Children with imperforate anus are at greater risk for injury to surrounding pelvic organs because these organs (such as vagina or urethra and seminal vesicles) are located immediately adjacent to the rectum, and may also be involved in the malformation in some unsuspected way.
    • During blind exploration in the pelvis, a dilated ureter can be mistaken for the rectum. Urethras can be opened or transected, and prostates or seminal vesicals can be easily injured. Dissection of these delicate structures can result in ischemia and possible stricture or complete stenosis.

Race

No known racial predilection has been reported.

Sex

No known sex predilection has been reported.

Age

Most children with an anorectal malformation are identified upon routine newborn physical examination. Delayed presentation is often the result of incomplete initial examination. Newborn anorectal and urogenital examination can be technically challenging and makes many practitioners uncomfortable.

Subtle malformations, such as those in some children with perineal fistula that may look normal to the casual glance, may present months or years after birth when the child presents to a primary care provider for constipation or urinary tract infection and appears to have a small perineal body upon physical examination.

Anorectal malformations in females with a normal-appearing anus who have absent vagina or persistent urogenital sinus may go undiagnosed for years because of examiner reluctance to separate the labia during physical examination. These malformations can be discovered upon evaluation for urinary tract infection or primary amenorrhea.

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Contributor Information and Disclosures
Author

Nelson G Rosen, MD, FACS, FAAP  Assistant Professor of Surgery and Pediatrics, Albert Einstein College of Medicine; Attending Pediatric Surgeon and Director, Pediatric Trauma Center, Department of Pediatric General Surgery, Schneider Children's Hospital

Nelson G Rosen, MD, FACS, FAAP is a member of the following medical societies: American Academy of Pediatrics, American College of Surgeons, American Pediatric Surgical Association, American Trauma Society, Association of Military Surgeons of the US, Canadian Association of Pediatric Surgeons, and Eastern Association for the Surgery of Trauma

Disclosure: Nothing to disclose.

Coauthor(s)

Daniel A Beals, MD  Attending Staff, Cornerstone Pediatric Surgery

Daniel A Beals, MD is a member of the following medical societies: American Academy of Pediatrics, American College of Physicians, American Pediatric Surgical Association, American Society for Bioethics and Humanities, Kentucky Medical Association, Society for Fetal Urology, Society of Critical Care Medicine, and Southeastern Surgical Congress

Disclosure: Nothing to disclose.

Specialty Editor Board

Hisham Nazer, MB, BCh, FRCP, DCh, DTM&H  Professor of Pediatrics, Consultant in Pediatric Gastroenterology, Hepatology and Clinical Nutrition, Bushnaq Medical Centre, University of Jordan

Hisham Nazer, MB, BCh, FRCP, DCh, DTM&H is a member of the following medical societies: Royal College of Paediatrics and Child Health, Royal College of Physicians, Royal College of Surgeons in Ireland, Royal College of Surgeons of Edinburgh, and Royal Society of Tropical Medicine and Hygiene

Disclosure: Nothing to disclose.

Mary L Windle, PharmD  Adjunct Associate Professor, University of Nebraska Medical Center College of Pharmacy; Pharmacy Editor, eMedicine

Disclosure: Nothing to disclose.

Carmen Cuffari, MD  Associate Professor, Department of Pediatrics, Division of Gastroenterology/Nutrition, Johns Hopkins University School of Medicine

Carmen Cuffari, MD is a member of the following medical societies: American College of Gastroenterology, American Gastroenterological Association, North American Society for Pediatric Gastroenterology, Hepatology and Nutrition, and Royal College of Physicians and Surgeons of Canada

Disclosure: Nothing to disclose.

Steven M Schwarz, MD, FAAP, FACN, AGAF  Professor of Pediatrics, Children's Hospital at Downstate, SUNY-Downstate Medical Center

Steven M Schwarz, MD, FAAP, FACN, AGAF is a member of the following medical societies: American Academy of Pediatrics, American College of Nutrition, American College of Physician Executives, American Gastroenterological Association, American Pediatric Society, Gastroenterology Research Group, New York Academy of Medicine, North American Society for Pediatric Gastroenterology and Nutrition, and Society for Pediatric Research

Disclosure: Curemark, LLC Consulting fee Board membership; Centocor, Inc. Grant/research funds Independent contractor; Johnson & Johnson, Inc. Grant/research funds Independent contractor

Chief Editor

Carmen Cuffari, MD  Associate Professor, Department of Pediatrics, Division of Gastroenterology/Nutrition, Johns Hopkins University School of Medicine

Carmen Cuffari, MD is a member of the following medical societies: American College of Gastroenterology, American Gastroenterological Association, North American Society for Pediatric Gastroenterology, Hepatology and Nutrition, and Royal College of Physicians and Surgeons of Canada

Disclosure: Nothing to disclose.

References
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Distal colostogram, posteroanterior view. The initial phase of augmented-pressure distal colostography aims to determine where the colostomy was placed in the colon and how much colon is available for pull-through, without taking down the colostomy.
Distal colostogram, lateral view. This image shows the second phase of distal colostography, in which the patient is placed in the lateral position. A radio-opaque marker is clearly visible in the lower right side of the image, marking the muscle complex on the skin. This image shows that the rectal pouch joins the urinary tract at the level of the bulbar urethra, a relatively common malformation in boys.
Bucket-handle malformation. The appearance of a band of skin overlying the sphincteric muscle complex is a common sign in a child born with imperforate anus and perineal fistula.
String-of-pearls malformation. This image shows white mucoid material within a perineal fistula. The fistula frequently extends anteriorly up the scrotum's median raphe.
Cloaca. This is the classic appearance of a girl with a cloacal malformation with a single perineal orifice. The genitals appear quite short, which is a finding consistent with cloaca.
Fourchette fistula. This malformation is somewhere halfway between perineal fistula and vestibular fistula. The fistula has a wet vestibular mucosal lining on its anterior half, but the posterior half is dry perineal skin.
 
 
 
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