Ano-rectal malformation

Question 1

What are anorectal malformations (ARM)?

Answer 1

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.

Question 2

Is there a racial difference in the incidence of anorectal malformations?

Answer 2

No, there are no racial differences in the incidence of ARM, although some families may have a genetic predisposition.

Question 3

What is the gender distribution for anorectal malformations

Answer 3

• Most studies report a male preponderance of 55-65%.
• High anomalies are more common in males, while low lesions are more common in females.

Question 4

How are anorectal malformations detected in newborns?

Answer 4

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.

Question 5

What are some antenatal signs of anorectal malformations (ARM)?

Answer 5

• 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)

Question 6

How is a malformation of the anorectal canal typically detected at birth?

Answer 6

• 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.

Question 7

What other perineal features should be documented in the case of anorectal malformations?

Answer 7

• Flattened buttocks
• The presence of a sacral dimple
• In cases of a cloaca, a single orifice may be present

Question 8

What are the signs of progressive abdominal distension and bowel obstruction in neonates with anorectal malformations?

Answer 8

• 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

Question 9

Why is a careful examination important in female infants with anorectal malformations?

Answer 9

• 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.

Question 12

What classification system is used for anorectal malformations?

Answer 12

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.

Question 13

How are high and low anorectal malformations different in terms of anatomy and prognosis?

Answer 13

• 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.

Question 14

How does associated sacral maldevelopment affect anorectal malformations?

Answer 14

• Maldevelopment of the sacrum impairs the innervation of both the anal and urethral musculature.
• This can lead to bladder and bowel dysfunction.

Question 15

What are the types of anorectal malformations with a rectal fistula in boys?

Answer 15

• Perineal fistula (most common)
• Recto-urethral fistula:
• Bulbar/membranous urethra
• Prostatic urethra
• Recto-vesical fistula (fistula inserts at the bladder neck) (<10%)

Question 16

What are the types of anorectal malformations with a rectal fistula in girls?

Answer 16

• Vestibular fistula (most common)
• Perineal fistula
• Recto-vaginal fistula (exceptionally rare, <1%)

Question 17

What is a cloacal malformation

Answer 17

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.

Question 18

What is the incidence of imperforate anus without a fistula?

Answer 18

Imperforate anus without a fistula occurs in less than 5% of cases in both boys and girls.

Question 19

What is the VACTERL association in anorectal malformations?

Answer 19

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

Question 20

Why is a detailed evaluation of each anatomical system important in patients with anorectal malformations?

Answer 20

A thorough evaluation is crucial to identify associated anomalies, as these defects can significantly impact the patient’s outcome and management.

Question 21

What is the first step in the evaluation of a child with an anorectal malformation?

Answer 21

Resuscitation:
• Assess the general condition of the baby
• Initiate resuscitation measures if necessary

Question 22

What measures should be taken for resuscitation in a baby with ARM?

Answer 22

• 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

Question 23

What is the next step after resuscitation in a child with an anorectal malformation?

Answer 23

Urgent referral to the nearest paediatric surgical unit for:
• A diverting colostomy (or primary anorectoplasty in selected cases)

Question 24

How should the perineum be examined to determine the type of anorectal malformation?

Answer 24

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

Question 25

How can a cross-table lateral shoot help in diagnosing anorectal malformations?

Answer 25

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.

Question 26

How can a babygram or neonatal x-ray help in diagnosing anorectal malformations?

Answer 26

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

Question 27

When should a babygram be performed in neonates with ARM?

Answer 27

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.

Question 28

What are some associated abnormalities to look for in anorectal malformations?

Answer 28

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

Question 29

What is the primary objective of surgical management in anorectal malformations?

Answer 29

The primary objective is to relieve the obstruction.

Question 30

What is the usual approach to surgical management in anorectal malformations?

Answer 30

Staged approach: 1. Primary divided sigmoid colostomy 2. Posterior Sagittal Anorectoplasty (PSARP) 3. Colostomy closure • This approach is typically followed in most cases.

Question 32

When might a primary pull-through surgery be performed in anorectal malformations?

Answer 32

• 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.

Question 33

What is the purpose of the mucous fistula in the management of anorectal malformations?

Answer 33

The mucous fistula allows mucous to drain from the distal sigmoid and rectum.

Question 34

Why is the mucous fistula important for surgical planning in anorectal malformations?

Answer 34

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

Question 35

What is the purpose of Pullthrough/PSARP surgery in anorectal malformations?

Answer 35

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

Question 36

When is Pullthrough/PSARP surgery typically performed?

Answer 36

It is performed at 3-6 months of age.

Question 37

How is the incision made during Pullthrough/PSARP surgery?

Answer 37

• 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.

Question 38

Can Pullthrough/PSARP surgery be done as a primary procedure in neonates?

Answer 38

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.

Question 39

What type of surgery is required for male patients with high lesions, such as rectovesical or rectoprostatic urethral fistulae?

Answer 39

For male patients with high lesions, such as rectovesical or rectoprostatic urethral fistulae, laparoscopic or laparotomy-assisted anorectoplasty is required.

Question 40

What type of surgery is required for female patients with complex cloacal malformations?

Answer 40

For female patients with complex, long common-channel cloaca malformations, laparoscopic or laparotomy-assisted anorectoplasty is required.

Question 41

When is the stoma closed after surgery for anorectal malformations?

Answer 41

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.

Question 42

Why might most patients require daily home dilation of the neo-anus?

Answer 42

• 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.

Question 43

How can stomal prolapse be prevented after anorectal surgery?

Answer 43

Stomal prolapse can be prevented by: • Stoma formation in the proximal sigmoid, just below the retroperitoneally-fixed descending colon • Ensuring proper surgical technique

Question 44

How can peri-stomal skin excoriation be prevented?

Answer 44

Peri-stomal skin excoriation can be prevented by using a properly fitting stoma appliance.

Question 45

How can perianal skin excoriation be prevented after anorectal surgery?

Answer 45

Perianal skin excoriation can be prevented by applying barrier creams to the buttocks.

Question 46

What post-operative complication might occur after PSARP surgery, and how can it be prevented?

Answer 46

• Wound breakdown can occur. • Adequate post-PSARP dilations are crucial to prevent anal stenosis.

Question 47

What factors contribute to long-term continence in patients with anorectal malformations?

Answer 47

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

Question 48

What is the prognosis for patients with “low lesions” in anorectal malformations?

Answer 48

• 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.

Question 49

What ongoing treatment is often required for patients with “low lesions” to maintain continence?

Answer 49

Life-long aggressive treatment with senna preparations (e.g. Senekot) to prevent fecal loading, which can lead to overflow incontinence.

Question 50

What are the typical continence outcomes for patients with “low lesions” after treatment?

Answer 50

Patients with low lesions may have occasional accidents and night-time soiling, but they are usually socially continent.

Question 51

What is the prognosis for patients with “high lesions” (e.g., rectovesical, recto-prostatic, long-common channel cloaca malformations) regarding continence?

Answer 51

• 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.

Question 52

What is a common method for patients with high lesions to manage continence?

Answer 52

Some patients opt to perform antegrade continence enemas (ACE) in a prograde manner through a special colostomy (e.g., button caecostomy or appendicostomy).

Question 53

What is essential for all children with anorectal malformations (ARM) in terms of follow-up care?

Answer 53

All children with ARM need follow-up in a unit familiar with appropriate bowel management programs.