Congenital malformations - Edocr

228 PART VI GASTROINTESTINAL MALFORMATIONS
TABLE 35-1 Classification of Anorectal
Malformations (Reprinted from Pena A, Hong
A. Advances in the management of anorectal
malformations. Am J Surg. Nov 2000;
180(5):370–6, with permission from Excerpta
Medica, Inc.)
Male Defects
• Perineal fistula
• Rectourethral bulbar fistula
• Rectourethral prostatic fistula
• Rectovesical (bladder-neck) fistula
• Imperforate anus without fistula
• Rectal atresia and stenosis
Female Defects
• Perineal fistula
• Vestibular fistula
• Imperforate anus with no fistula
• Rectal atresia and stenosis
• Cloaca
rectovestibular fistula is by far the most common
defect in females. 2,7
Genetic predisposition plays a role in some
infants as there is an increased incidence of consanguinity
and an increased risk of recurrence
in siblings. In addition, anorectal malformations
in association with a well recognized syndrome
may also have an identifiable genetic etiology.
However, no clear etiology can be identified in
large majority of infants with isolated anorectal
malformations. Recently, a higher incidence of
anorectal malformations after in utero exposure
to lorazepam and a lower incidence of anorectal
malformations after maternal folic acid supplementation
have been reported but require
further confirmation. 8,9
EMBRYOLOGY
Developmentally, the cloaca, the expanded terminal
part of hindgut, is the most complex region
of the hindgut. Between the sixth and seventh
weeks of gestation, the cloaca is divided by the
urorectal septum into the urogenital sinus ventrally
and the anorectal portion dorsally. The
anorectal portion of the cloaca develops into the
rectum and the superior two-thirds of the anal
canal; the inferior one-third of the anal canal develops
from the ectoderm of proctodeum. The
normal development of the urorectal septum
also divides the cloacal membrane into the urogenital
diaphragm anteriorly and the anal membrane
posteriorly. Approximately at the end of
the eighth week of gestation, the anal membrane
ruptures creating the anal opening. Most anorectal
anomalies result from abnormal development
of the urorectal septum and cloacal membrane.
CLINICAL PRESENTATION
Most infants are diagnosed at or soon after birth
when no anal opening is noted on physical examination
or because of failure to pass meconium.
Abdominal distension and emesis are late findings
in these infants, but can dominate the clinical
presentation in infants with delayed or missed
diagnosis.
ASSOCIATED MALFORMATIONS
AND SYNDROMES
Associated malformations are present in 50–70%
of infants with anorectal malformations 10,11 and
emphasize the need for a thorough evaluation
because these coexisting anomalies account for
significant morbidity and mortality in these infants.
The genitourinary and musculoskeletal
anomalies are most frequent. Table 35-2 summarizes
commonly reported associated malformations
in these infants. The more common urinary
anomalies in these infants are hydronephrosis
and vesicoureteral reflux. Varying degree of sacral
abnormalities are most common skeletal malformations
and presence of a sacral abnormality significantly
increases the chances of an associated
genitourinary malformation. Boys with anorectal
malformations are much more likely to have genitourinary
anomalies. 12