Anorectal malformations (imperforate anus) !
- Malformation
The rectum does not open to the outside, or opens in the wrong place such as the urethra or vestibule; it is found on the newborn exam.
Updated 2026-11-01
See it in 3D: Anal canal · Rectum · External anal sphincter · Urinary bladder
What it is
They are a spectrum of defects in which the rectum ends blindly, opens through a fistula to the urethra, bladder, vagina or perineum, or the anus is narrow or absent. They arise from abnormal development of the urorectal septum and cloaca in the embryonic period. They are classed as high or low by the level of the blind pouch relative to the puborectalis muscle and are often part of the VACTERL association.
Embryological cause
- Weeks 4 to 7 approx.: the urorectal septum must grow down to the cloacal membrane and separate the anorectal canal from the urogenital sinus.
- If the septum falls short or deviates, the rectum stays connected to the urogenital sinus: rectourethral, rectovesical or rectovestibular fistulas.
- If the anal membrane does not rupture or the anal pit forms poorly, a membrane or a low stenosis remains.
- A persistent cloaca in girls reflects complete failure of division.
How it presents
- No anal opening on the newborn exam, or an anus in an abnormal position.
- No passage of meconium, followed by distension and vomiting.
- Meconium in the urine (urinary fistula in boys) or from the vestibule (girls).
- Associations: VACTERL, tethered cord, sacral anomalies and Down syndrome.
Diagnosis
- Careful perineal exam in the first hours, looking for a fistula.
- Prone cross-table lateral X-ray, after about 24 hours, to estimate the distance from the pouch to the skin.
- Renal and spinal ultrasound, echocardiogram and spine X-rays to look for VACTERL.
Test yourself
Think of the answer, then tap the question to see it.
Which embryonic structure fails in anorectal malformations?
The urorectal septum, which does not completely divide the cloaca into urogenital sinus and anorectal canal.
Which finding suggests a rectourinary fistula in a boy?
Meconium coming from the urethra or mixed in the urine.
Which muscle defines a malformation as high or low?
The puborectalis: a pouch ending above it is high and one ending below it is low.
Which association of malformations is screened for in these newborns?
VACTERL: vertebral, anorectal, cardiac, tracheoesophageal, renal and limb defects.
See it in 3D
The structures of Durgical's 3D anatomy where it is found.
Related
- Hindgut and cloaca: the urorectal septum and the pectinate line
- Esophageal atresia and tracheoesophageal fistula
- Hemivertebra, congenital scoliosis and Klippel–Feil
- Renal agenesis and the Potter sequence
- Hirschsprung disease (congenital aganglionic megacolon)
- Bladder exstrophy
- Bladder, urachus and urethra
Related conditions
Educational content on embryonic development; not a guide to prenatal diagnosis or to medicines in pregnancy and no substitute for a health professional's advice. No doses are given.
Sources: Embryology, Rectum and Anal Canal (StatPearls Publishing (NCBI Bookshelf), 2023); Imperforate anus (MedlinePlus, U.S. National Library of Medicine, 2025).
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Representative model, for educational purposes only.