Gastrointestinal Radiology > Procedures > Defecography > Defecography (11)

Defecography (cont.)

Anorectal Disorders Exhibiting Pathologic Defecograms (cont.)

Rectal Intussusception And Prolapse
  • Rectal intussusception is an abnormal condition in which the proximal rectal wall invaginates into the distal rectum during defecation and persists after the bolus has passed.
  • When the lead point of the intussusceptum passes beyond the external anal orifice, the condition is designated rectal prolapse.
  • During downward straining, the intussusceptum occludes the anal canal, preventing further evacuation of rectal contents. The most common symptoms are constipation, incomplete emptying, rectal bleeding, perineal pain or pressure, and fecal incontinence. However, mild mucosal intussusception may also occur in subjects without anorectal symptoms.

  • Rectal intussusception has three stages of severity:
    • Stage I, rectal intussusception: A mucosal fold develops in the rectal wall and gradually deepens to form an intussusception of the full thickness of the rectal wall into the rectal lumen. However, a minimal infolding that disappears after the bolus has passed is probably caused by transient invagination of the rectal mucosa and should not be considered pathologic.
    • Stage II, intraanal rectal intussusception: The apex of the rectal intussusceptum passes down into the anal canal.
    • Stage III, rectal prolapse: The intussusception passes through the anal canal and protrudes externally. It is termed a complete external rectal prolapse when the entire thickness of the rectal wall protrudes beyond the anus. Partial prolapse is the designation when the protrusion consists of mucosa only.
  • In some patients, this process develops gradually and slowly so that it is easy to recognize. In others, the rectal wall prolapses suddenly, only at the end of rectal evacuation, so that it is necessary to ask the patient to evacuate as completely as possible during the examination.
  • Most intussusceptions originate from the anterior wall (60%) or begin in an annular fashion (30%). The posterior wall is rarely the origin.  Intussusception most often develops at the level of a valve of Houston, approximately 6-8 cm from the anal margin.
  • All patients with an intussusception have a concomitant rectocele. In patients who develop external rectal prolapse, the rectum assumes a vertical axis and is displaced away from the curve of the sacrum when the patient is straining.
  • The anatomical prerequisite for a rectal intussusception to occur is that the proximal rectum is an intraperitoneal organ. In such cases, the normal retroperitoneal position is changed, and there is a mesorectum present. The abnormal attachment of the rectum may or may not be accompanied by a deep pouch of Douglas.

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