Imperforate Anus

The Concept

Imperforate anus (anorectal malformation) is a congenital abnormality in which the normal anal opening is absent or abnormally formed, resulting from failure of normal development of the anorectum. It is an important neonatal surgical condition, recognised at the first newborn examination, and it exists as a spectrum of severity.

Classification — Low VS High

The malformations are broadly divided by the level at which the rectum ends relative to the levator ani (puborectalis):

• Low anomalies — the rectum has descended through the levator (e.g. An anal membrane, anal stenosis, or an ectopic/covered anus); generally simpler to correct.
• High anomalies — the rectum ends above the levator, often with a fistula to the urethra or bladder (in boys) or the vagina (in girls); more complex.

It is often part of the vacterl association of anomalies, so a search for other defects is needed.

Clinical Features & Management

At birth there is no anal opening, failure to pass meconium, and progressive abdominal distension; passage of meconium in the urine indicates a fistula. Assessment uses examination, an invertogram/X-ray (to judge the level) and ultrasound (for associated anomalies). Management depends on the level: a low lesion is treated by anoplasty, while a high lesion is managed by an initial defunctioning colostomy, followed by a definitive pull-through (posterior sagittal anorectoplasty, PSARP), and later closure of the colostomy.

A Note on the Importance of Associated Anomalies

A key management point is the frequent association with other congenital anomalies, captured in the vacterl acronym — Vertebral, Anorectal, Cardiac, Tracheo-Esophageal, Renal and Limb defects. Because these often occur together, a neonate with an anorectal malformation should be screened for the other components (with echocardiography, renal ultrasound and spinal imaging). Overlooking a serious associated cardiac or renal anomaly can be more dangerous than the anorectal lesion itself, which is why systematic screening is emphasised.

The Bottom Line

Imperforate anus is a congenital anorectal malformation (low or high, often with a fistula) presenting in the newborn, assessed for its level and for vacterl anomalies, and treated by anoplasty (low) or colostomy and later pull-through/PSARP (high).

A Note on Early Recognition at Birth

The importance of the routine newborn examination cannot be overstated: imperforate anus should be detected at the first inspection of the perineum after birth, before feeding is established and distension develops. Early recognition allows timely referral, prevents the complications of a missed obstruction (distension, vomiting, aspiration, perforation), and gives time to screen for associated anomalies. A simple, careful look at the anus in every newborn is therefore the key to a good outcome in this condition.

Level relative to the levator ani determines the operation.

• Imperforate anus (anorectal malformation) = congenital absence/abnormality of the anal opening; neonatal surgical condition.
• Low (rectum through levator — anal membrane/stenosis/ectopic anus) vs high (rectum above levator, often with fistula to urethra/bladder/vagina); part of vacterl association.
• Presents at birth: no anal opening, no meconium passed, abdominal distension; meconium in urine = fistula.
• Assess with invertogram/X-ray + ultrasound; low → anoplasty; high → colostomy → definitive pull-through (PSARP) → colostomy closure.