Selected Gastrointestinal Anomalies in the Neonate
Richard J. Martin MBBS, FRACP, in Fanaroff and Martin's Neonatal-Perinatal Medicine, 2020
Anorectal Anomalies
Anorectal malformations, or
imperforate anus, are a class of
congenital malformations that covers a wide spectrum of defects.38,74,77 They can be quite minor in appearance—for example, a mildly anteriorly displaced anus—or quite severe. Overall, most patients do reasonably well, with more than 75% attaining a good degree of bowel control when they have adequate treatment.77 The most severe forms of pelvic malformations, such as cloacal exstrophy, are not discussed here; this discussion is limited to malformations of the anus and
rectum alone.
Imperforate anus occurs in 1 of every 4000-5000 newborns. The estimated risk for a couple having a second child with an
anorectal malformation is approximately 1%. The frequency of this defect is slightly higher in male than in female patients.
Traditionally, the terms high, intermediate, and low were used to describe various degrees of imperforate anus. However, terminology should relate to the location of the rectal
fistula for both prognostic and therapeutic implications.
More than 80% of male patients with imperforate anus have a fistulous connection between the rectum and the
urinary tract. This can go from the rectum to the
bladder (rectovesical), to the prostatic
urethra (rectoprostatic), and to the bulbar urethra (rectobulbar). When the
rectal fistula opens onto the perineal skin, it is called a
perineal fistula. An unusual form of imperforate anus occurs when the rectum ends blindly in the pelvis. More than 50% of these patients have Down syndrome and almost all patients with Down syndrome and imperforate anus have this variant.
