Evacuation proctography

Evacuation proctography (defecography) is a fluoroscopic technique to evaluate pelvic floor disorders. The technique traditionally involves fluoroscopy and barium, but an analogous MRI technique has also been developed (see: MR dynamic pelvis imagingdefaecating proctography).

Indications

• incomplete defecation / constipation
• pelvic floor disorder
• rectal prolapse
• faecal incontinence

Contraindications

• postoperative rectum (e.g. coloanal anastomosis)
  • caution should be exercised before loading and stressing an anastomosed rectum

Procedure

The patient should take an adequate bowel prep the night before.

Right before the exam takes place, opacification of the vagina and, in some institutions, the small bowel should be performed if the patient is female. This is done to watch the movement of these structures in relation to the rectum during defecation. Men only typically require opacification of the rectum.

• vagina 
  • amount of contrast varies between institutions, but 5 ml is used at some
  • barium should be more viscous than PO barium
  • not performed if patient has never been sexually active
• small bowel
  • 500 ml of barium PO
  • wait 30-60 minutes
  • if not at terminal ileum on a scout radiograph, additional 200 ml of barium and another 30-60 minutes

Positioning/room set up

The fluoroscopy table should be able to accomodate a special commode for the purpose of receiving evacuated rectal barium

Technique

First, vaginal and small bowel (some institutions) contrast should be administered, as above. Then, the procedure can begin:

• patient is first in left lateral decubitus position
  • 2-4 x 60 ml of thick barium paste is introduced into the rectum with a large bore soft catheter (Miller catheter) and the 60 ml syringes
  • barium may be mixed with breadcrumbs to form a solution with stool-like consistency (neostool)
  • if the patient has an urge to defecate, the instillation of contrast can cease
• spot lateral images of the patient at rest in the left lateral decubitus position
  • knees are drawn up in this position, as if the patient were sitting
• patient is positioned on the commode / defecography chair and a right lateral view of the seated patient is readied
  1. spot image of the patient at rest
  2. cine and spot images of the patient "lifting" their rectum (Kegel maneuver)
  3. cine and spot images of the patient straining as if they were about to defecate, but not actually defecating
  4. then, finally, the patient should "go like they would go at home" and spot and cine images are taken while the patient evacuates their rectum
  5. A postevacuation image with straining should be obtained to look for retained material or enterocoele

Practical points

It should always be remembered that, even if this procedure is routine for the radiologist and technician, this is a highly invasive and sensitive test for the patient. The patient should be given maximum privacy at all times.

Measurements

In evaluating evacuation proctography images, the key reference line is drawn from the tip of the coccyx to the lower border of the pubic ramus. Ascent and descent of various structures is measured in relation to this line.

In evaluating rectal motion, one measurement often used is the change in the anorectal angle (ARA). This angle is formed by intersection of a line parallel to the anal canal and a line parallel to the posterior rectum. The change in the anorectal angle is an an indirect indication of the strength of the puborectalis muscle.

Normal movements/measurements

• during straining (increased intra-abdominal pressure), the pelvic floor descends a few cm
• during evacuation, the anorectal angle becomes much more obtuse and the anorectal junction descends (<3.5 cm, usually to level of the ischial tuberosities)
  • there is a wide range of normal for both the rest and evacuation angles, but 90-95 degrees at rest and 135 degrees at evacuation is not unreasonable
  • loss of puborectalis sling impression on the posterior wall of the distal rectum