What are the different types of anorectal atresia in newborns?

Types of Anorectal Atresia in Newborns

Anorectal atresia is classified into three main anatomical categories based on the level of the defect relative to the levator ani muscle complex: supralevator (high), intermediate, and translevator (low) types. 1

Anatomical Classification System

High (Supralevator) Atresia

• The rectal pouch terminates above the levator ani muscle complex 1
• These defects typically require more complex surgical reconstruction due to poor development of the pelvic musculature 2
• MRI is particularly useful in larger/older patients for assessing pelvic muscle development and predicting functional outcomes 2

Intermediate Atresia

• The rectal pouch lies at the level of the levator ani muscle 1
• Represents a transitional anatomical position between high and low defects 1

Low (Translevator) Atresia

• The rectal pouch extends below the levator ani muscle with a fully developed sphincter complex 1
• In females, this can present as anus perinei ventralis, where a perineal fistula opens just behind the vaginal entrance with the sphincter complex located dorsally 1
• These defects are more amenable to perineal repair without colostomy 2

Specific Anatomical Variants

Membranous Rectal Atresia

• An extremely rare variant (1-2% of all anorectal malformations) where a membrane obstructs the rectal lumen 3, 4
• The anal opening appears normal externally, but a membrane blocks passage of meconium 3
• Can present with prolapsed pinkish mass at the anal margin 3
• May be managed with transanal membrane excision without colostomy in selected cases 4

Rectal Stenosis

• Another rare variant accounting for only 1-2% of anorectal malformations 3
• Represents partial rather than complete obstruction 3

Critical Clinical Considerations

Diagnostic approach varies by defect level:

• In newborns with suspected high atresia, MRI helps determine whether perineal repair is feasible versus requiring colostomy 2
• Plain radiography with invertogram and red rubber catheter can classify the atresia level in resource-limited settings, though MRI provides superior detail 4
• The level of atresia directly correlates with sphincter muscle development and long-term continence outcomes 2

Associated anomalies are common:

• VACTERL associations (vertebral, anorectal, cardiac, tracheal, esophageal, renal, limb abnormalities) occur frequently 5
• Jejunoileal atresia can co-occur with anorectal malformations, though this is rare and may be missed on initial workup 5
• Tethered cord, sacral deformities, and urinary tract abnormalities should be actively sought 2

Surgical planning depends on anatomical type:

• Low defects with adequate sphincter development: primary perineal repair (Peña procedure) 1
• High defects with poor pelvic musculature: staged repair with initial colostomy 4
• Membranous variants: may allow primary transanal approach without diversion 4