++
The spectrum of anorectal malformations (ARMs) ranges from anal
stenosis to persistent cloaca. The term imperforate anus applies
to most of these malformations because the anal canal is malformed
and there is no visible normal anal opening onto the perineum. Anorectal anomalies
occur in as many as one in 4000 live births and are slightly more
common in boys. The most common defect is an imperforate anus with
a fistula between the distal anorectum and the urethra in boys,
or the vestibule in girls. The risk of a second child with an anorectal
malformation is approximately 1%.
++
The embryologic development of the hindgut is discussed in Chapter 381. By 6 weeks of gestation, the
urorectal septum divides the cloaca into the anterior urogenital
sinus and posterior anorectal canal. Failure of the urorectal septum
to form results in a fistula between the bowel and urinary tract
(male) or the vagina or vestibule (female). The urorectal septum
divides the cloacal membrane into the urogenital and anal membranes.
Failure of the anal membrane to resorb results in an anal membrane
or stenosis. The perineum also contributes to development of the
external anal opening and genitalia by formation of cloacal folds
that extend from the anterior genital tubercle to the anal membrane.Breakdown
of the cloacal folds results in the external anal opening being
anterior to the external sphincter (ie, anteriorly displaced anus
or perineal fistula).
+++
Clinical Features
and Diagnostic Evaluation
++
Anorectal malformations represent a wide spectrum of defects
and should be ultimately described in terms of the realized anatomy,
rather than “low or high” as is often customary
(Table 415-1). The terms high or low, are
used to generalize the location of the distal rectum or anal canal
relative to the perineum. High lesions are those in which the rectum
ends above the levator musculature and may or may not have a fistulous
connection to the vagina, prostatic urethra, bladder neck, or bladder.
Intermediate lesions are characterized by the rectal pouch ending
within the levator complex, with or without a fistula to the vestibule or the bulbar urethra
in boys. In low lesions, the rectal pouch has completely traversed
the levator musculature, and a fistula usually is evident on the
skin within the midline (perineal fistula). Rectal atresia refers
to an unusual lesion in which the lumen of the rectum is either
completely or partially interrupted, with the upper rectum being
dilated and the lower rectum consisting of a small anal canal. Anal
stenosis can be seen in both males and females and is characterized
by a normally positioned anal perineal orifice with a narrowed anal
canal. A persistent cloaca is a female defect in which the rectum,
vagina, and urethra all empty into a single, common channel.
++
++
When evaluating the neonate with an anorectal malformation, a
meticulous perineal inspection and thorough physical examination
are crucial (eFig. 415.1). The examiner
should recognize the fact that congenital anorectal anomalies often
coexist with other lesions, and the VACTERL association must be
considered (Table 415-2). Bony abnormalities
of the sacrum and spine occur in about one third of patients with anorectal
anomalies and consist of absent, accessory, or hemivertebrae or
an asymmetric or short sacrum. The absence of two or more sacral
elements is associated with a poor prognosis for bowel or bladder
continence. Occult dysraphism of the spinal cord also may be present—tethered
cord, lipomeningocele, or fat within the filum. Genitourinary abnormalities
other than the rectourinary fistula occur in 26% to 59% of
patients. Vesicoureteral reflux and hydronephrosis are the most
common abnormalities, but other findings such as horseshoe, dysplastic,
or absent kidney as well as hypospadias or cryptorchidism must also
be sought. In general, the “higher” the anorectal
malformation, the more frequent the associated urologic abnormalities.
In patients with persistent cloaca or rectovesical fistula, the
likelihood of a genitourinary abnormality is approximately 90%.
In contrast, the frequency is only 10% in children with “low” defects
(ie, perineal fistula).
++
++
++
Evaluation for associated anomalies mandates a thorough radiographic
workup prior to definitive surgical management. Plain-film radiography
is performed to evaluate for bony abnormalities of the vertebrae,
sacrum, and limbs. Echocardiography should be performed in every
infant to exclude structural congenital heart disease. Ultrasonography
of the spine is obtained to exclude occult spinal dysraphism, and
if an abnormality is noted, neurosurgical consultation should be
obtained.1 Before feeding, a nasogastric tube should
be placed, and its presence within the stomach should be confirmed
to exclude esophageal atresia. Radiographic evaluation of the urinary
tract should include renal ultrasonography and a voiding cystourethrogram
if clinically indicated. The latter should be obtained in every
infant with a high or complex malformation.
++
Pediatric surgical consultation should be sought promptly when
faced with a neonate with an anorectal malformation. In experienced hands,
inspection of the perineum alone determines the level of the distal
rectum in 80% of boys and 90% of girls. In the
male, the generally accepted distance that would allow for safe primary
repair is 1 cm or less. For evaluation of a newborn male with an
anorectal anomaly, a 24-hour period of observation allows the distal rectum
to fill with air or meconium in order to facilitate assessment of
the distance between perineal skin and the distal rectum. In the
intervening time, the previously outlined radiographic workup for
VACTERL association and further studies to determine the distance between
the rectum and perineum are performed. A cross-table lateral radiograph
with the infant in the prone position and a radiopaque marker on
the perineal skin will allow for this determination in some cases.
Alternatively, ultrasonography can be utilized to achieve the same
goal when experienced personnel are available to perform the examination. Clinical assessment
coupled with these radiographic adjuncts allows for an adequate
surgical plan to be formulated in the majority of cases. Otherwise,
a colostomy is performed in males with a distal rectum that is unclear
or higher than the level of the coccyx, meconium-stained urine,
or other life-threatening anomalies (ie, tracheoesophageal fistula
or severe structural cardiac disease). If primary repair is not
performed, a colostomy is performed followed by a definitive repair
1 month after colostomy or when other anomalies have been adequately
addressed or corrected. Performance of definitive repair at this
time (after 1 month) allows for limited time with a colostomy, less
size discrepancy between the proximal and distal bowel at the time
of colostomy closure, ease of postoperative anal dilation, and fewer
recognizable sequelae from perineal manipulation, and this may afford
an advantage in terms of potential for acquired perineal sensation.
++
Evaluation of a female with an anorectal anomaly requires a thorough
perineal inspection to differentiate between a cloaca, vestibular
fistula, perineal fistula, or an anteriorly displaced anus. A single
perineal orifice is consistent with a persistent cloaca and should always
prompt a diverting colostomy. In females with a vestibular fistula,
primary neonatal repair should be reserved for those with extensive
primary surgical correction of the defect.2 Most
pediatric surgeons, despite their level of experience, perform a
diverting colostomy with the expectation to perform definitive repair
several months later owing to the technical difficulty of separating the
rectum from the vagina and the complications that may be realized
if that portion of the operation is compromised.
++
The newborn infant with anal stenosis, perineal fistula, or an
anteriorly displaced anus can usually undergo a primary, single-stage
procedure without a colostomy. Three basic approaches may be used. For
anal stenosis, simple dilatation is often successful. Initially,
a dilator size is chosen commensurate with what the anal canal will
accommodate without significant trauma to the anal canal. Dilations proceed
twice daily, and the size of dilator is progressively increased
at regular intervals under the guidance of a pediatric surgeon.
The frequency of dilation is tapered and discontinued after the
appropriate anal canal diameter is achieved (12-Fr size for infants—about
the size of the adult index finger).
++
If there is a very small distance from the anal opening and the
center of the external sphincter, and the perineal body (the distance
between the most inferior aspect of the introitus in a female and
the most posterior aspect of the scrotal raphe in a male) is intact
and of adequate length, a cutback anoplasty is performed. Under
general anesthesia, an incision is made posteriorly from the anal orifice
through the central part of the anal sphincter. A posterior anoplasty
is performed and this effectively enlarges the anal opening. Alternatively,
if there is a large distance between the anal opening and the central
portion of the external anal sphincter or the perineal body is short,
an anal transposition, or minimal posterior sagital anorectoplasty
is performed. This operation involves transposition of the aberrant
anal opening posteriorly to the correct position within the sphincter
complex, and the perineal body is reconstructed.
++
Patients with other anorectal malformations require an initial
colostomy, as the first part of a three-stage reconstruction. The
colon is completely divided in the sigmoid region, with the proximal
bowel as the colostomy and the distal bowel as a mucous fistula. Prior
to maturing the mucous fistula, the distal bowel is completely evacuated
of meconium. Complete division of the bowel minimizes fecal contamination
into the area of a rectourinary fistula, and it may lessen the risk
of urosepsis. The distal bowel can later be evaluated radiographically
to determine whether the rectum terminates with a fistulous connection
to the urethra, bladder neck, bladder, vagina, or as a blind ending
pouch.The second-stage of the procedure usually is performed 1 to
6 months later, depending on the nature of the anomaly and the overall
status of the patient. Definitive reconstruction consists of surgically
dividing the fistulous connection with the urinary tract or vagina
if present and pulling the terminal rectal pouch through the anal
sphincter mechanism to the normal anal position with a procedure
known as a posterior-sagital anorectoplasty. The central position
of the anal sphincter is identified by electrical stimulation of
the perineum.3 Following anorectoplasty, a urinary
catheter remains in place for 5 to 14 days to maintain the lumen
of the urethra after repair of rectourinary fistula or cloaca. Perioperative
antibiotics are administered for 24 hours, and sitz baths are allowed
1 week postoperatively. Two weeks after the anorectoplasty, a program
of anal dilatations is started. The neoanus is initially calibrated
to determine the size of dilator initially selected by the operating
surgeon in either the office or operating room. Twice-daily dilations
are then performed by the caregiver and the size advanced every
1 to 2 weeks until the desired size is reached (age 1 to 3 months:
12 mm dilator, age 4 to 8 months: 13 mm, age 9 to 12 months: 14
dilator). Once the desired size is reached, the “third
stage” of the operative plan is completed—colostomy
closure. Dilations must be continued until the appropriate size
can be passed easily, and they are thereafter tapered over the course
of several weeks.
+++
Prognosis and Outcomes
++
Fecal continence is the principal goal of the surgical repair
of any anorectal malformation. The most common postoperative sequelae
seen in children with these malformations include constipation, soiling,
and incontinence. Prognostic factors for continence include the
level of the rectum and whether the sacrum is normal. In general,
the best results with regard to continence are seen in patients with
low lesions and a normal sacrum.
++
Children who are completely free of soiling and have voluntary
bowel movements are deemed totally continent. Although most children
do not begin toilet training until 2 to 3 years of age, prior signs
allow one to predict the possibility of successful continence in
these children. Good prognostic signs include 1 to 3 bowel movements
a day without interval soiling, evidence of sensation while defecating (pushing
or making faces), a normal sacrum, well-formed and contoured buttocks,
and urinary control. Ultimately, each patient must be treated individually
based on the anatomy of the defect and the patient’s functional
outcome.
++
Children with perineal fistula, rectal atresia, anteriorly displaced
anus, and rectovestibular fistula have a high likelihood of total
continence but more commonly experience constipation. This may result
from a history of discomfort or pain during passage of bowel movements
leading to a learned behavior with contraction of the pelvic floor
to prevent the stool from passing. A downward spiral of constipation,
overflow-soiling, mega-sigmoid, and dysmotility can ensue. Ensuring
soft, painless, and regular bowel movements is important to prevent
withholding behavior. Treatment strategies for patients with constipation
and overflow incontinence are similar to those discussed in Chapter 386. In children with constipation
but without withholding behavior, it is important to assure that
there is no anatomic obstruction from stenosis at the anastomosis
or incontinence via a fistula (digital examination or barium enema).
++
The parents of children with poor-prognosis defects should be
educated about the expected outcome. Bowel-management techniques should
focus on a goal of social continence, similar to strategies used for
patients with spinal anomalies. Management strategies include the
use of loperamide to slow the bowel transit and the frequency of
fecal incontinence episodes, especially during the daytime.4-6
++
Children with rectoprostatic urethral fistula, rectovesicular
fistula, or complex cloaca are more prone to incontinence and are
often reliant on a bowel-management program to prevent fecal incontinence
and social isolation. In general, this program utilizes maneuvers
to keep the colon clean throughout the day while controlling the
need to defecate, including retrograde or anterograde enemas (following placement
of a cecostomy or appendicostomy).7 Anorectal biofeedback
may improve continence in some older children with low to intermediate
lesions and good sphincter function.