Anorectal Malformation - Coggle Diagram
Terminal hindgut placement abnormalities outside or partially outisde the sphincter mechanism
Average worldwide incidence: 1 in 5000 live births.
Male preponderance: 55% to 65% of cases.
Most common defect in females: Rectovestibular fistula.
Most common defect in males: Rectourethral fistula.
Imperforate anus without fistula occurs in 5% of patients.
Those with Down syndrome and ARMs have imperforate anus without fistula 95% of the time.
2/3 of males have high abnormality
2/3 of females have low abnormality
Cloacal Formation (Week 3):
The cloaca, a U-shaped cavity, forms during embryogenesis.
Around the 21st day of gestation, the hindgut, allantois, and later the mesonephric ducts open into the cloaca.
A septum, known as the urorectal septum, grows downward and fuses with lateral folds (Rathke's plicae), dividing the cloaca into two cavities: a urogenital cavity anteriorly and an anorectal cavity posteriorly.
This process is completed by the 6th week of gestation.
Cloacal Membrane and Division (Week 7):
The cloacal membrane, initially intact, breaks down around the 7th week of gestation.
This breakdown results in the creation of two separate openings: the urogenital opening anteriorly and the anal opening posteriorly.
The orientation of the cloacal membrane is altered due to the rapid growth of the genital tubercle, leading to its displacement posteriorly.
Defective Formation Theories:
Old Theory: Attributes ARMs to defective formation of the urorectal septum, explaining a wide variety of defects in both males and females.
Newer Theory: Suggests that defects in the shape of the dorsal cloaca and an absence of the dorsal cloacal membrane contribute to the development of ARMs.
Classification (Pena System)
Rectobladder neck fistula
Imperforate anus without fistula
3 cm common channel
<3 cm common channel
Imperforate anus without fistula
Present in approximately one-third of patients with ARMs.
Most common cardiac lesions include atrial septal defects and patent ductus arteriosus.
Cardiac anomalies necessitate thorough cardiovascular evaluations and considerations in the overall treatment plan.
Gastrointestinal (GIT) Anomalies:
Tracheoesophageal abnormalities occur in about 10% of cases.
Duodenal atresia is observed in 1% to 2% of cases.
Coexistence of ARM with GIT anomalies emphasizes the need for comprehensive imaging and management strategies.
Lumbosacral anomalies are frequent, including hemivertebrae, scoliosis, butterfly vertebrae, and hemisacrum.
The association of imperforate anus with sacral defects, particularly hemisacrum, is known as the Currarino triad.
Incidence ranges from one-third to half of patients with ARMs.
Vesico-ureteric reflux is the most common genitourinary anomaly.
Renal agenesis and dysplasia are frequently observed.
Cryptorchidism is reported in up to 20% of males with imperforate anus, and hypospadias occurs in approximately 5%.
Hydrocolpos can lead to urinary obstruction or pyocolpos.
Uterine malformations, predominantly bicornuate uterus and uterus didelphys, may coexist.
Vaginal abnormalities, particularly a vaginal septum, can be present.
Clinical features and management
Clinical Findings and Management in Male Babies:
Thorough Perineal Inspection:
Initial assessment to identify important clues about the type of malformation.
Timing of Decision-Making:
Delay decisions on colostomy or primary operation until 20 to 24 hours of age.
Intraluminal Pressure and Meconium:
Avoid decisions before 20 to 24 hours as intraluminal pressure is needed for meconium to pass through a fistula, a valuable sign for determining distal rectum location.
Radiologic assessments may not reflect accurate anatomy before 24 hours due to sphincter muscle tone.
Intravenous Fluids and Monitoring:
Newborns should receive intravenous fluids, antibiotics, and nasogastric decompression in the first 24 hours.
If meconium is visible on the perineum, indicating a rectoperineal fistula, anoplasty can be performed in the newborn period without a protective colostomy.
Cross-Table Lateral X-ray:
If no meconium is seen after 24 hours, perform a cross-table lateral x-ray to determine the rectal gas location.
Management depends on the location of rectal gas and associated defects.
Clinical Findings and Management in Female Babies:
Initial assessment to identify the type of malformation.
Associated Defects Evaluation:
Rule out serious associated defects within the first 24 hours.
Perineal Fistula or Vestibular Fistula:
Anoplasty can be performed without a colostomy if a fistula is present.
For patients with cloaca, a right transverse colostomy is recommended, saving the distal colon for potential use as a vaginal substitute.
Surgical Approach in Male Babies:
Rectoprostatic and Bulbar Fistulae:
Approach: Posterior sagittal approach.
Progressive soft tissue division in the midline.
Opening the posterior wall of the rectum to visualize the fistula.
Separation of the rectum from the urinary tract.
Reconstruction of the muscle complex around the mobilized rectum.
Rectobladder Neck Fistula:
Options: May involve a laparotomy or laparoscopy.
Initial separation of the rectum from the bladder.
Depending on the approach, either continue with a posterior sagittal approach or pull the mobilized rectum from below within the area of maximal muscle contraction.
Guidance: Distal colostography is performed before proceeding with definitive reconstruction.
The anatomy of the ARM is delineated.
Visualization of the recto-urinary fistula.
Careful planning for subsequent steps in the procedure.
[Include Figures 11.11, 11.12, and 11.13 here]
Surgical Approach in Female Babies:
Approach: Posterior sagittal operation.
Emphasis: Special attention to separating the rectum from the vagina.
Careful dissection to separate the rectum from the anteriorly positioned vagina.
Addressing the common wall without a distinct plane of separation.
Consideration of the surgeon's experience in deciding between primary repair and colostomy.
Goal: Separation of the rectum from the vagina and urinary tract.
Common Channel Length: Assessed by endoscopy.
Variation in Procedure:
Common channel length < 3 cm: Managed by the posterior sagittal approach.
Common channel length > 3 cm: Requires a more extensive procedure, potentially involving a laparotomy and vaginal replacement with a segment of bowel.
[Include Figure 11.14 here]
Considerations for One-Stage Repair:
In some cases, one-stage repair can be considered in neonates without colostomy.
Decision based on the surgeon's experience and the general condition of the patient.
Continence: The higher the ARM anomaly, the lower the achieved continence.
Sacral Anomalies: Associated with decreased achieved continence.
Constipation: Lower malformations tend to suffer more from constipation