Canis ISSN: 2398-2942

Anus: atresia

Contributor(s): James Simpson

Introduction

  • Congenital condition of the anal opening and the terminal rectum resulting in closure of the anal outlet or abnormal routing of feces.
  • Signs: tenesmus, bulging of the perineum, absence of feces, abdominal distension and discomfort.
  • Diagnosis: physical examination, history of tenesmus, lack of feces.
  • Treatment: surgical.
  • Prognosis: guarded due to surgical complications.

Pathogenesis

Etiology

  • Congenital.

Pathophysiology



Type I
  • A membrane over the anal opening remains, with the rectum ending as a blind pouch just cranial to the closed anus.
Type II
  • The anus is closed as in Type I but the rectal pouch is located somewhat cranial to the membrane overlying the anus.
Type III
  • The rectum ends as a blind pouch cranially within the pelvic canal (rectal atresia) while the terminal rectum and anus are normal.
Type IV
  • In females, atresia ani exists with a persistent communication between the rectum and vagina (rectovaginal fistula). This fistula can occur with a normal anal opening as well. The cause of this condition is failure of the cloacal membrane to resorb or rupture by the second month of embryonal development; hence, continuity between the rectum and anus is impaired. The result of this defect is an altered defecation behavior resulting in outpouching of the anal region and abnormal vaginal discharges.
All Types
  • All types usually have an intact external anal sphincter and its associated nerve supply, although the sphincter may be poorly developed.

Timecourse

  • Acute.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers


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