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 births.
Clinically there is no anal opening. It can be broadly be classified into high (supralevator) or low (infralevator) subtype depending on location of the atretic portion.
Most cases tend to be sporadic with occasional familial forms
There are frequent associations with other congenital abnormalities.
- other atresias
- VACTERL association
- caudal regression syndrome (has associated sacral agenesis and lower limb hypoplasia
- may have fistulous tracts with the
- or have a single cloacal opening
- can be variable depending on the site of atresia (e.g high or low) , level of impaction with meconium and physiological effects such as straining
- may show multiple dilated bowel loops with with 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).
Distance of gas bubble in rectum from the metal piece is noted:
- >2 cm: denotes high type
- <2 cm: denotes low type
Fluoroscopy: contrast study
- to detect recto-urinary, recto-vaginal or rectoperineal fistula
- the fistula is considered low (below levator ani plane) if it is below the pubooccygeal line (PCL) and considered high fistula if above the PCL
- 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 infra coccygeal or transperineal approach may allow differentiation between a high or low subtype 4
- 1. Harris RD, Nyberg DA, Mack LA et-al. Anorectal atresia: prenatal sonographic diagnosis. AJR Am J Roentgenol. 1987;149 (2): 395-400. AJR Am J Roentgenol (abstract) - Pubmed citation
- 2. Berrocal T, Lamas M, Gutieérrez J et-al. Congenital anomalies of the small intestine, colon, and rectum. Radiographics. 19 (5): 1219-36. Radiographics (full text) - Pubmed citation
- 3. Han TI, Kim IO, Kim WS. Imperforate anus: US determination of the type with infracoccygeal approach. Radiology. 2003;228 (1): 226-9. doi:10.1148/radiol.2281011900 - Pubmed citation
- 4. Entezami M, Albig M, Knoll U et-al. Ultrasound Diagnosis of Fetal Anomalies. Thieme. (2003) ISBN:1588902129. Read it at Google Books - Find it at Amazon
- 5. Donnelly L, Jones B, O'hara S et-al. Diagnostic imaging. AMIRSYS. ISBN:141602333X. Read it at Google Books - Find it at Amazon