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MRI anatomy of anteriorly displaced anus: what obstructs defecation?

Amr Abdelhamid AbouZeid1, Shaimaa Abdelsattar Mohammad, Khaled Talaat Khairy

  • 1Department of Pediatric Surgery, Ain-Shams University, Ramsis Street, Abbassya, Cairo, 11566, Egypt, amrabdelhamid@hotmail.com.

Pediatric Radiology
|April 24, 2014
PubMed

Insights

Anteriorly displaced anus in children involves the distal anal canal shifting forward, impacting defecation. MRI reveals an obtuse anorectal angle, explaining obstructed bowel movements in these cases.

Area of Science:

  • Pediatric Surgery
  • Radiology
  • Gastroenterology

Background:

  • Anteriorly displaced anus is a congenital anomaly with debated nomenclature, diagnosis, and management.
  • Understanding its anatomical basis is crucial for effective treatment.

Purpose of the Study:

  • To delineate the magnetic resonance imaging (MRI) anatomy of the anal canal in children diagnosed with anteriorly displaced anus.
  • To investigate the impact of this anatomical variation on the defecation process.

Main Methods:

  • Prospective study of ten children (7 girls, 3 boys; age 7 months–8 years) with anteriorly displaced anus.
  • Noncontrast MRI (1.5-T) using T1- and T2-weighted images in axial, sagittal, and coronal planes.
  • Measurement of anorectal angle and hiatal distance, compared to controls using Mann-Whitney test.

Main Results:

  • No proximal anal canal abnormalities were found.
  • Distal anal canal displacement anteriorly, outside the external muscle cuff, was observed.
  • Children with anteriorly displaced anus exhibited a significantly more obtuse anorectal angle (mean 112.1°) compared to controls (mean 86.2°).

Conclusions:

  • MRI is effective for visualizing anal canal anatomy in anteriorly displaced anus.
  • Abnormal longitudinal muscle orientation across the anal canal likely causes obstructed defecation.
  • MRI may aid in evaluating equivocal cases and children with unexplained constipation.
Abstract

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