Anal atresia

Anal atresia, or imperforate anus, refers to a spectrum of anorectal abnormalities ranging from a membranous separation to complete absence of the anus.

The estimated incidence is 1 in 5000 live births.

Clinically there is no anal opening. Subtypes can be classified into two broad categories: high (supralevator) or low (infralevator), depending on the location of the atretic portion.


Most cases are sporadic, with occasional familial forms


There are frequent associations with other congenital abnormalities.

Abdominal radiograph
  • can be variable depending on the site of atresia (i.e. high or low), level of meconium impaction and physiological effects such as straining
  • may show multiple dilated bowel loops with an absence of rectal gas

A coin/metal piece is placed over the expected anus and the baby is turned upside down (for a minimum 3 minutes).

The distance of the gas bubble in the rectum from the metal piece is noted:

  • >2 cm denotes high type
  • <2 cm denotes low type
Fluoroscopy: contrast study
  • to detect a recto-urinary, rectovaginal, or rectoperineal fistula
  • the fistula is considered low (below the levator ani plane) if it is below the pubococcygeal line (PCL) and high if above it
  • the anus may be seen as an echogenic spot at the level of the perineum and in an atresia this echogenic spot may be absent 4
  • may show bowel dilatation
  • an infracoccygeal or transperineal approach may allow differentiation between high and low subtypes 4
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Article information

rID: 6365
Tag: cases
Synonyms or Alternate Spellings:
  • Imperforate anus
  • Atresia of the anus

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Cases and figures

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    Case 1
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    Case 2: with recto-urethral fistula
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    Case 3: with lateral to confirm position
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    High type anal at...
    Case 4
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