Anorectal Malformations

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ARM Intro - Embryo's Oopsie

  • ARM: A spectrum of congenital defects involving an absent or abnormally located anus, and an improperly developed rectum.
  • Embryo's Hiccup:
    • Failure of the cloaca to correctly divide into urogenital sinus and anorectum.
    • This crucial separation by the urorectal septum happens between weeks 5-7 of gestation.
  • Associated Syndromes:
    • VACTERL association is a significant co-occurrence.
    • Look for spinal (tethered cord) and genitourinary malformations.

⭐ Incidence: Affects roughly 1 in 5000 live births. Anorectal Malformations: Female and Male Typesoka

ARM Spectrum - Classifying the Chaos

ARMs present a spectrum of defects; precise classification is key for management and prognosis. The Krickenbeck classification is the standard.

⭐ The Krickenbeck classification is based on the fistula's location and is crucial for surgical planning.

Key Determinant: The presence and anatomical site of the fistula. "Low" lesions generally have better functional prognosis than "High" lesions.

  • Krickenbeck Categories:
    • Males:
      • Perineal Fistula (PF): Opening on perineal skin.
      • Rectourethral Fistula (RUF): Connection to urethra.
        • Bulbar (lower)
        • Prostatic (higher)
      • Rectovesical (Bladder Neck) Fistula: Connection to bladder; highest, most complex.
      • ARM without Fistula
      • Rectal Atresia/Stenosis
    • Females:
      • Perineal Fistula (PF): Opening on perineal skin.
      • Vestibular Fistula: Opening in vulvar vestibule; most common in females.
      • Cloaca: Single perineal opening for urinary, genital, and rectal tracts. Common channel length > 3 cm implies ↑ complexity.
      • ARM without Fistula
      • Rectal Atresia/Stenosis
      • Rectovaginal Fistula (very rare)

Anorectal Malformations: Female and Male Classifications

ARM Diagnosis - Uncovering Clues

  • Clinical Presentation:
    • Absent/ectopic anal opening (perineal, vestibular).
    • Flat "bottom", single perineal dimple.
    • Meconium from vagina, urethra, or perineum.
    • Failure to pass meconium (24-48 hrs); abdominal distension.
  • Key Investigations:
    • Perineal Inspection: Essential initial step.
    • Prone Cross-table Lateral X-ray: Done 18-24 hrs post-birth.
      • Measures gas bubble to skin marker distance.
      • High: > 1 cm; Low: < 1 cm.
    • Perineal Ultrasound (USG): Accurate pouch-perineal distance, usable < 24 hrs.
    • Distal Colostogram: Pre-definitive repair; defines pouch anatomy/fistula.
    • VCUG: For suspected rectourinary fistula.
    • MRI: Complex ARMs, cloaca, tethered cord.
  • Screening for Associated Anomalies (📌 VACTERL):
    • Vertebral: Spinal X-ray/USG.
    • Cardiac: Echocardiogram.
    • Tracheo-Esophageal: NG tube passage, CXR.
    • Renal: Abdominal USG.
    • Limb: Clinical exam, X-rays if needed. Screening for newborns with anorectal malformation (ARM)

⭐ Associated anomalies are common, with VACTERL association seen in up to 70% of cases.

ARM Management - Surgical Solutions

  • Initial Management (High/Intermediate ARM):
    • Stabilize patient.
    • Diverting colostomy (sigmoid) within 24-48 hours if high/intermediate anomaly or no perineal fistula.
    • Allows bowel decompression & growth.
  • Definitive Repair:
    • Posterior Sagittal Anorectoplasty (PSARP) is standard for most high/intermediate ARMs.
    • Performed at 1-3 months (or ~5-10 kg).
    • Laparoscopic-assisted PSARP (LASARP) for higher lesions.
  • Low ARM Management:
    • Primary perineal procedures (e.g., anoplasty, fistuloplasty) in neonatal period.
    • Colostomy usually avoided for simple perineal fistulas.

⭐ Posterior Sagittal Anorectoplasty (PSARP) is the standard surgical approach for most intermediate and high ARMs.

PSARP for Anorectal Malformation: Steps a-e

High‑Yield Points - ⚡ Biggest Takeaways

  • Anorectal Malformations (ARM) are a spectrum, from imperforate anus to complex cloaca.
  • Strongly associated with VACTERL syndrome; look for other anomalies.
  • Prone cross-table lateral X-ray or invertogram assesses pouch height and fistula.
  • High lesions typically need initial colostomy, then PSARP (Posterior Sagittal Anorectoplasty).
  • Low lesions may allow primary anoplasty or minimal PSARP.
  • Fistula location (perineal, vestibular, urethral, vesical) is key for surgical planning.
  • Post-op challenges include constipation and fecal incontinence requiring long-term follow-up.

Practice Questions: Anorectal Malformations

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