Anorectal Malformations

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ARM Basics - No Exit? Embryo Mix‑Up

  • Definition: A spectrum of congenital anomalies where the anus is absent, abnormally located, or stenosed.
  • Incidence: Approximately 1 in 5000 live births.
  • Embryology (Weeks 7-8):
    • Failure of caudal descent of urorectal septum (incomplete cloaca division).
    • Or, failure of anal membrane (cloacal membrane remnant) perforation. Anorectal Malformations in Females and Males

VACTERL Association is seen in a significant percentage:

  • Vertebral defects
  • Anal atresia
  • Cardiac defects
  • Tracheo-Esophageal fistula
  • Renal anomalies
  • Limb abnormalities

ARM Types - Classifying Cloacal Chaos

Krickenbeck classification is primary. Wingspread (High, Intermediate, Low) provides an older grouping.

Krickenbeck TypeGenderAnatomy HighlightCommon Sign
Perineal FistulaM/FTract to perineal skinMeconium on perineum
RectourethralMTract to bulbar/prostatic urethraMeconium in urine
RectovesicalMTract to bladder neckMeconium in urine, flat bottom
Vestibular FistulaFTract to vaginal vestibuleSingle perineal opening (apparent)
CloacaFRectum, vagina, urethra join; channel >3cmSingle perineal opening
ARM (No Fistula)M/FBlind rectal pouchNo meconium, distension

⭐ Most common ARM: Males - Rectourethral fistula; Females - Rectovestibular fistula.

ARM Clues - Diagnosis Detective

  • Clinical Signs: Absent anal opening, failure to pass meconium within 24 hrs, abdominal distension. Meconium in urine (fistula), on perineum ("fly speck"), or in vagina.
  • Investigations:
    • Thorough perineal inspection: Look for fistulas.
    • Prone cross-table lateral X-ray or Invertogram (Wangensteen-Rice): Gas bubble > 1 cm from skin marker suggests low pouch.
    • USG (renal, spinal), Echocardiogram (cardiac).
    • Complex/high lesions: Distal colostogram, MRI.
  • Associated Anomalies: 📌 VACTERL (Vertebral, Anal, Cardiac, Tracheo-Esophageal, Renal, Limb).

⭐ Presence of perineal meconium (e.g., "bucket handle" sign, "fly speck" meconium) usually indicates a low malformation with a perineal fistula.

ARM Fixes - Tailoring the Tail‑End

  • Initial Management: IV fluids, NG tube, antibiotics.
  • Colostomy:
    • Indicated for high/intermediate lesions, or unstable patients.
    • Typically divided sigmoid colostomy.
    • Done in neonatal period if ARM not suitable for primary repair.
  • Definitive Repair:
    • Posterior Sagittal Anorectoplasty (PSARP - Pena procedure): Gold standard.
    • Anterior Sagittal Anorectoplasty (ASARP).
    • Laparoscopic-Assisted Anorectal Pull-through (LAARP).
    • Timing:
      • Low lesions: Primary repair (neonatal).
      • High/Intermediate (post-colostomy): Definitive repair usually at 1-3 months of age.
  • Cloaca: Complex, requires individualized staged repair.

⭐ PSARP allows direct visualization and reconstruction of the muscle complex, crucial for future continence.

PSARP surgical steps

ARM Aftercare - Post‑Op Plumbing Puzzles

  • Early Complications:
    • Wound issues: infection, dehiscence.
    • Anal problems: stricture, mucosal prolapse.
    • Recurrent fistula.
  • Late Complications:
    • Constipation (most common).
    • Fecal incontinence & soiling.
    • Urinary incontinence (esp. with cloaca/high lesions).
  • Prognostic Factors:
    • Type of ARM.
    • Sacral development: Sacral Ratio < 0.4 indicates poor prognosis. Sacral Ratio and Curvature Measurement for ARM Prognosis
    • Associated spinal anomalies.
    • Surgical technique quality.
  • Bowel Management Program (BMP) is crucial for long-term continence.

⭐ Long-term bowel function is significantly influenced by sacral quality and the presence of spinal anomalies.

High‑Yield Points - ⚡ Biggest Takeaways

  • VACTERL association is common; screen for other anomalies.
  • Invertogram is historical; use cross-table lateral X-ray or ultrasound initially.
  • Fistula site (perineal, rectourethral, vestibular) dictates ARM type & surgical approach.
  • High ARMs usually need colostomy then PSARP; low ARMs may allow primary repair.
  • Distal colostogram or MRI is vital for high lesions to define pouch anatomy.
  • Sacral issues (e.g., ratio < 0.4, tethered cord) predict poorer continence.
  • Cloaca (females): complex ARM, common channel, needs specialized reconstruction.

Practice Questions: Anorectal Malformations

Test your understanding with these related questions

Oesophageal atresia may occur as part of the VACTERL group of anomalies. What does "TE" refer to in this context?

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Flashcards: Anorectal Malformations

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Most commonly occuring complication of undescended testes is increased risk of _____

TAP TO REVEAL ANSWER

Most commonly occuring complication of undescended testes is increased risk of _____

inguinal hernia

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