Ano-rectal malformation Flashcards
What are anorectal malformations (ARM)?
ARM are a group of anomalies caused by abnormal development of the hindgut, allantois, and Mullerian ducts. They occur in about 1 in 5,000 live births.
Is there a racial difference in the incidence of anorectal malformations?
No, there are no racial differences in the incidence of ARM, although some families may have a genetic predisposition.
What is the gender distribution for anorectal malformations
• Most studies report a male preponderance of 55-65%.
• High anomalies are more common in males, while low lesions are more common in females.
How are anorectal malformations detected in newborns?
Routine newborn examinations typically detect ARM early. However, anterior ectopic anus and anal stenosis may be less easily detected and might present later with chronic constipation or pain.
What are some antenatal signs of anorectal malformations (ARM)?
• Polyhydramnios (excess amniotic fluid)
• Antenatal ultrasound may show:
• Thickened, dilated bowel loops suggestive of lower intestinal obstruction
• Associated VACTERL anomalies (vertebral, anorectal, cardiac, tracheoesophageal, renal, and limb malformations)
How is a malformation of the anorectal canal typically detected at birth?
• An imperforate anus may be noted on visual inspection of the perineum, such as:
• No normally sized anal opening at the site of the anal sphincter
• An anal dimple without an anal opening
• A fistula to the perineum or vestibule in females
• A blank perineum with no signs of an anus
• If patency is in doubt, gently probe the anus with a lubricated, bent-over loop of a nasogastric tube.
What other perineal features should be documented in the case of anorectal malformations?
• Flattened buttocks
• The presence of a sacral dimple
• In cases of a cloaca, a single orifice may be present
What are the signs of progressive abdominal distension and bowel obstruction in neonates with anorectal malformations?
• Abdominal distension
• Vomiting, including bile-stained vomitus
• Failure to pass meconium
• Passing meconium does not exclude an anorectal malformation as meconium may pass through a rectal fistula
• There may be evidence of meconium in the urine or on the perineum
Why is a careful examination important in female infants with anorectal malformations?
• Girls need a very thorough examination, as it is easy to miss a vestibular or perineal lesion.
• Females may present later with these anomalies, leading to a delayed diagnosis.
What classification system is used for anorectal malformations?
The Krickenbeck classification is used for anorectal malformations.
• It classifies ARM based on the anatomical level of the distal rectum and whether there is a connection from the blind-ending rectum to another organ or the skin.
How are high and low anorectal malformations different in terms of anatomy and prognosis?
• High lesions:
• The rectum does not pass through the puborectalis muscle.
• These lesions are more likely to result in long-term continence problems.
Low lesions:
• The rectum traverses the puborectalis muscle complex.
• These lesions have a better prognosis and are more likely to have perineal or posterior fourchette fistulas.
How does associated sacral maldevelopment affect anorectal malformations?
• Maldevelopment of the sacrum impairs the innervation of both the anal and urethral musculature.
• This can lead to bladder and bowel dysfunction.
What are the types of anorectal malformations with a rectal fistula in boys?
• Perineal fistula (most common)
• Recto-urethral fistula:
• Bulbar/membranous urethra
• Prostatic urethra
• Recto-vesical fistula (fistula inserts at the bladder neck) (<10%)
What are the types of anorectal malformations with a rectal fistula in girls?
• Vestibular fistula (most common)
• Perineal fistula
• Recto-vaginal fistula (exceptionally rare, <1%)
What is a cloacal malformation
A cloacal malformation occurs when the urethra, vagina, and rectum all drain into a single common channel with a single perineal opening instead of three separate openings.
What is the incidence of imperforate anus without a fistula?
Imperforate anus without a fistula occurs in less than 5% of cases in both boys and girls.
What is the VACTERL association in anorectal malformations?
The VACTERL association refers to a group of anomalies that frequently occur together in patients with anorectal malformations:
• V: Vertebral anomalies (25%)
• A: Anal anomalies (ARM itself)
• C: Cardiac anomalies (10%)
• T: Tracheoesophageal anomalies (10%)
• R: Renal/genito-urinary anomalies (25%)
• L: Limb anomalies
Why is a detailed evaluation of each anatomical system important in patients with anorectal malformations?
A thorough evaluation is crucial to identify associated anomalies, as these defects can significantly impact the patient’s outcome and management.
What is the first step in the evaluation of a child with an anorectal malformation?
Resuscitation:
• Assess the general condition of the baby
• Initiate resuscitation measures if necessary
What measures should be taken for resuscitation in a baby with ARM?
• Nasogastric tube decompression:
• Helps decompress the stomach and rule out oesophageal atresia
Intravenous fluids:
• Start intravenous maintenance fluids
• Correct intravascular fluid deficits (from vomiting or fluid sequestration in the obstructed bowel) with boluses of 10-20 ml/kg of 0.9% NaCl
What is the next step after resuscitation in a child with an anorectal malformation?
Urgent referral to the nearest paediatric surgical unit for:
• A diverting colostomy (or primary anorectoplasty in selected cases)
How should the perineum be examined to determine the type of anorectal malformation?
Examine the perineum to document the following:
• Presence, position, and number of openings
• Associated features like flattened buttocks
• Check for meconium in the urine (indicates urethral fistula) by placing gauze over the penis in boys
• Look for any opening or meconium coming out anywhere on the perineum between the expected anus and urethral meatus
• It may take >24 hours for enough pressure to build up to force meconium through a narrow fistula
How can a cross-table lateral shoot help in diagnosing anorectal malformations?
A cross-table lateral shoot is taken 24 hours after birth to help determine the anal orifice location.
• The baby is placed prone with the buttocks elevated.
• A radio-opaque marker is placed at the suspected anal orifice.
• Swallowed air serves as a contrast medium, allowing the distance between the rectum and skin to be estimated more accurately.
How can a babygram or neonatal x-ray help in diagnosing anorectal malformations?
A babygram provides information about:
• Amount of intestinal dilatation
• Presence of free air if perforation is suspected
• Evaluation of bony elements like ribs and vertebrae
• Identification of sacral agenesis or a poorly developed sacrum
• In cases of suspected tracheoesophageal fistula or oesophageal atresia, the nasogastric tube may be seen curled up in the upper oesophagus with paucity of distal bowel gas
When should a babygram be performed in neonates with ARM?
It should be performed 20-24 hours after birth.
• Swallowed air generates increased intra-luminal pressure, distending the bowel and forcing meconium through a fistula, providing a more accurate view.
• Performing it too early may create a false impression of a very short rectum.
What are some associated abnormalities to look for in anorectal malformations?
Cardiac:
• Look for cyanosis and listen for a cardiac murmur
• Perform a chest x-ray to assess the cardiac shadow and check for plethoric lung fields
• Even without murmurs, perform an electrocardiogram and echocardiogram
• Spinal:
• Examine for spinal abnormalities, dysmorphic facies, or radial limb abnormalities
• An MRI of the spine should be booked at 3-6 months to evaluate spinal cord anomalies
Renal:
• Perform a kidney, ureter, and bladder (KUB) ultrasound
What is the primary objective of surgical management in anorectal malformations?
The primary objective is to relieve the obstruction.
What is the usual approach to surgical management in anorectal malformations?
Staged approach:
1. Primary divided sigmoid colostomy
2. Posterior Sagittal Anorectoplasty (PSARP)
3. Colostomy closure
• This approach is typically followed in most cases.
When might a primary pull-through surgery be performed in anorectal malformations?
• A primary pull-through can be done in some larger, healthier babies who present early and have low defects such as a vestibular or perineal fistula.
What is the purpose of the mucous fistula in the management of anorectal malformations?
The mucous fistula allows mucous to drain from the distal sigmoid and rectum.
Why is the mucous fistula important for surgical planning in anorectal malformations?
It is crucial for surgical planning as it:
• Allows contrast to be injected into the distal bowel
• Helps visualize the exact location of the fistulous connection between the atretic anorectal canal and the urogenital tract
• Can identify fistulas that are not apparent on perineal inspection
What is the purpose of Pullthrough/PSARP surgery in anorectal malformations?
Definitive surgery to:
• Dissect the atretic anorectal canal
• Divide the fistula
• Place the anorectal canal and neo-anus within the funnel-shaped anal sphincter fibres
When is Pullthrough/PSARP surgery typically performed?
It is performed at 3-6 months of age.
How is the incision made during Pullthrough/PSARP surgery?
• The incision is made exactly in the midline between the buttocks to avoid injury to the muscle fibres of the sphincter complex.
• Electrostimulation is used to identify the sphincter complex.
Can Pullthrough/PSARP surgery be done as a primary procedure in neonates?
Yes, in selected cases with low lesions (perineal/vestibular fistulae), it can be performed as a primary, one-stage procedure without a covering colostomy, provided surgical expertise is available.
What type of surgery is required for male patients with high lesions, such as rectovesical or rectoprostatic urethral fistulae?
For male patients with high lesions, such as rectovesical or rectoprostatic urethral fistulae, laparoscopic or laparotomy-assisted anorectoplasty is required.
What type of surgery is required for female patients with complex cloacal malformations?
For female patients with complex, long common-channel cloaca malformations, laparoscopic or laparotomy-assisted anorectoplasty is required.
When is the stoma closed after surgery for anorectal malformations?
The stoma is closed only after the neo-anus has healed completely and is confirmed to be the correct size for the patient’s age.
Why might most patients require daily home dilation of the neo-anus?
• Most patients require daily home dilation of the neo-anus until the correct size is achieved because the anus tends to narrow with healing.
• This occurs because the cicatrix at the mucocutaneous junction is circular.
How can stomal prolapse be prevented after anorectal surgery?
Stomal prolapse can be prevented by:
• Stoma formation in the proximal sigmoid, just below the retroperitoneally-fixed descending colon
• Ensuring proper surgical technique
How can peri-stomal skin excoriation be prevented?
Peri-stomal skin excoriation can be prevented by using a properly fitting stoma appliance.
How can perianal skin excoriation be prevented after anorectal surgery?
Perianal skin excoriation can be prevented by applying barrier creams to the buttocks.
What post-operative complication might occur after PSARP surgery, and how can it be prevented?
• Wound breakdown can occur.
• Adequate post-PSARP dilations are crucial to prevent anal stenosis.
What factors contribute to long-term continence in patients with anorectal malformations?
Factors include:
• Comorbidities (e.g. sacral abnormalities causing neurogenic incontinence, neurodevelopmental problems like in Trisomy 21)
• Surgical technique (good placement of the neo-anus within the sphincter mechanism)
• Prevention of anal stenosis
What is the prognosis for patients with “low lesions” in anorectal malformations?
• Low lesions (e.g. rectoperineal fistulae, rectovestibular fistulae, bulbar urethral fistulae, short-common channel cloacae) generally have a good prognosis, provided that:
• Constipation is aggressively treated.
What ongoing treatment is often required for patients with “low lesions” to maintain continence?
Life-long aggressive treatment with senna preparations (e.g. Senekot) to prevent fecal loading, which can lead to overflow incontinence.
What are the typical continence outcomes for patients with “low lesions” after treatment?
Patients with low lesions may have occasional accidents and night-time soiling, but they are usually socially continent.
What is the prognosis for patients with “high lesions” (e.g., rectovesical, recto-prostatic, long-common channel cloaca malformations) regarding continence?
• High lesions (e.g., rectovesical, recto-prostatic, long-common channel cloaca malformations) are unlikely to be continent and typically require rectal washouts daily to evacuate the distal colon.
• This helps them to be socially continent while wearing normal underwear at school and work.
What is a common method for patients with high lesions to manage continence?
Some patients opt to perform antegrade continence enemas (ACE) in a prograde manner through a special colostomy (e.g., button caecostomy or appendicostomy).
What is essential for all children with anorectal malformations (ARM) in terms of follow-up care?
All children with ARM need follow-up in a unit familiar with appropriate bowel management programs.
