Anorectal Malformation

Anorectal malformations are congenital abnormalities in which the anus and distal rectum fail to develop normally.

The spectrum ranges from a mildly anterior or stenotic anus to complex rectal communication with the urinary tract, vagina or bladder.

The operative objective is not simply creation of an opening. A functional reconstruction requires placement of the rectum accurately within the sphincter complex while preserving urinary, genital and neurological structures.

Practical Krickenbeck classification

Common major types include:

Perineal fistula

Rectum opens onto the perineal skin anterior to the expected anal position.

Rectourethral fistula in boys

Can connect to:

• Bulbar urethra

• Prostatic urethra

Prostatic fistulas are generally anatomically higher.

Rectovesical fistula

Rectum communicates with the bladder neck or bladder.

High malformation.

Rectovestibular fistula

Rectum opens into the vestibule posterior to the vagina.

Common female malformation.

Cloaca

Rectum, vagina and urinary tract join into a common channel.

Requires highly specialised reconstructive planning.

No fistula

Blind rectal pouch without communication.

Anal stenosis

An anatomically present but abnormally narrow anal canal.

These anatomical categories are more useful for operative planning than simply calling the lesion \"high\" or \"low\". A recent surgical evidence review supports anatomy based classification and tailored operative management. ([pubmed.ncbi.nlm.nih.gov](https://pubmed.ncbi.nlm.nih.gov/38997855/))

Every newborn should undergo careful perineal inspection.

Assess:

• Is an anus present?
• Is it in the correct position?
• Is meconium emerging from the perineum?
• Is meconium present in urine?
• Is meconium emerging from the vestibule?
• Is there a single perineal opening in a girl?

In boys:

Meconium in urine strongly suggests rectourinary fistula.

In girls:

Identify separately:

• Urethral opening
• Vaginal opening
• Rectal or fistula opening

A single opening suggests cloaca until proven otherwise.

Do not repeatedly probe fistulas aggressively because tissue trauma can complicate definitive reconstruction.

Perform systematic evaluation for associated anomalies.

Important associations include:

• Sacral abnormalities
• Spinal cord tethering
• Renal abnormalities
• Vesicoureteric reflux
• Cardiac defects
• Oesophageal atresia
• Limb abnormalities

Obtain:

• Renal and pelvic ultrasound
• Echocardiography where indicated
• Sacral radiograph
• Spinal ultrasound in a young infant or MRI when appropriate

Infant without visible fistula

Allow approximately the first 18 to 24 hours for distal bowel gas and meconium to reach the rectal pouch when the infant is clinically stable.

A prone cross table lateral radiograph can then estimate the relationship between the rectal pouch and perineum.

Do not use an old fashioned upside down invertogram.

After colostomy

Before definitive repair of a rectourinary fistula, perform a high pressure distal colostogram.

This is one of the most important investigations because it identifies:

• Fistula location
• Distal rectal anatomy
• Relationship to urinary tract
• Rectal length

A poorly performed low pressure study can miss the fistula.

Initial newborn management

Keep nil orally when obstruction is significant.

Provide IV fluids.

Insert gastric decompression when abdominal distension or vomiting is present.

The decision is between:

• Primary perineal repair

and

• Diversion with later definitive reconstruction

Perineal fistula

A well defined low perineal fistula can often undergo primary repair without colostomy.

Options include:

• Limited anoplasty
• Posterior sagittal anorectoplasty when deeper mobilisation is required

The rectum must be placed within the centre of the sphincter complex.

Rectovestibular fistula

Definitive repair is usually posterior sagittal anorectoplasty or an equivalent perineal approach.

Primary neonatal repair can be successful in selected stable infants at experienced centres.

A staged approach with colostomy can be preferable when there is:

• Major distension
• Sepsis
• Poor local anatomy
• Significant associated illness
• Limited specialist resources

Rectourethral and rectovesical fistula

These generally require more extensive mobilisation.

A common strategy is:

• Divided sigmoid colostomy
• Allow growth and complete anatomical evaluation
• Distal colostogram
• Definitive posterior sagittal or laparoscopic assisted anorectoplasty
• Later colostomy closure

The fistula must be separated from the urinary tract without damaging:

• Urethra
• Bladder neck
• Vas deferens
• Seminal structures

Colostomy

When diversion is required, a divided descending or sigmoid colostomy with separate mucous fistula is preferred.

The proximal stoma should permit easy appliance fitting.

The distal mucous fistula permits:

• Distal irrigation
• Colostogram
• Decompression

Avoid placing the stoma too distally because adequate colon is required for later pull through.

Posterior sagittal anorectoplasty

The posterior sagittal approach divides the midline sphincter complex under direct vision.

Use muscle stimulation to identify the functional sphincter.

The rectum is:

• Separated from urinary or genital fistula
• Mobilised without compromising blood supply
• Positioned centrally within the muscle complex
• Anastomosed to perineal skin

Cloaca

Persistent cloaca requires specialised multidisciplinary reconstruction.

Assessment includes:

• Common channel length
• Urethral length
• Vaginal anatomy
• Müllerian anatomy
• Renal function
• Hydrocolpos

Hydrocolpos causing urinary obstruction requires drainage.

Definitive reconstruction may require:

• Posterior sagittal approach
• Total urogenital mobilisation
• Separation of rectum from urogenital tract
• Vaginal reconstruction

Complex cloaca should be managed in a specialist paediatric colorectal and urology centre.

Postoperative anal dilatation

A structured dilation programme is often used after anoplasty or PSARP to prevent anastomotic stenosis.

The required calibre depends on age and reconstructive anatomy.

Do not perform traumatic forceful dilatation.

Long term continence

Continence depends heavily on:

• Sacral development
• Spinal cord integrity
• Sphincter muscle quality
• Malformation type
• Quality of rectal placement

Children with poor continence potential can achieve social cleanliness using structured bowel management.

Options include:

• Diet
• Laxatives
• Enemas
• Antegrade continence enema procedures

Long term care should aim for predictable bowel emptying, not simply accept chronic faecal soiling.