Defecography: A Procedure For Rectal Function

Sometimes my patients come to their appointments with me after undergoing a defecography test. They receive the report, but don't understand the findings, so I spend some time going over and reviewing the report with them. You don't know what you don't know, and I am a firm believer in knowledge, especially about one's own body. So I wanted to go over the nitty gritty of defecography within this post.

Defecography is a "fluoroscopic examination for patients with defecation difficulties because it enables a functional, real time assessment of the defecation mechanics in a physiologic setting" (Kim, 2011).

The procedure begins with a barium paste inserted into the patient's rectum. The staff will continue inserting the barium paste until the patient feels the urge to defecate. The amount of paste is usually around 250 to 300 mL by this time.

Depending on where you go for your defecography procedure, it may differ on how the next steps in the procedure occur. I had one patient tell me she sat on a special toilet right then and there. Another had a table tilt until vertical and a commode was placed for the patient to sit on. Either way, while there, the radiologist will provide instructions for the patient to follow. These instructions are to help a patient mimic the mechanics of pooping so the radiologist knows when to record what a patient's muscles are doing, or not doing, as the case may be.

The duration of the procedure may be from 30 to 60 minutes.

What is being assessed?

The puborectal angle is being assessed. This angle is measured "between the longitudinal axis of anal canal and the posterior rectal line, parallel to the longitudinal axis of the rectum" (Kim, 2011). This angle is an "indirect indicator of the puborectal muscle activity" (Kim, 2011). The average value at rest for this angle is 95-96 degrees, physiologic range 65-100 degrees, and without much difference between men and women.

When the muscles contract, that angle becomes more acute (less than 95-96 degrees) while becoming more obtuse (increase in degrees) when the muscle relaxes.

The other aspect looked at is the anorectal junction, which is the top of the anal canal. Radiologists want to see what happens to this junction when a patient strains during defecation. The movement of the anorectal junction ascending/descending represents how the pelvic floor is moving.

Defecography may also be used for imaging on how a patient voids as well.

Normal Findings

Anorectal angle: about 90 degrees

Pelvic floor muscle contraction: anorectal angle is about 75 degrees, junction moves upward

Evacuation: anorectal angle increases with "the relaxation of anal sphincter and puborectalis muscle."

Straining: anorectal angle increases while the pelvic floor descends

Another thing that radiologists look at are reference lines referred to as H line and M line.

H line: "from the inferior margin of the pubic symphysis to the posterior aspect of the anorectal junction, and represents the diameter of the levator hiatus" (radiopaedia.org).

Normal: less than 6 cm

Mild: 6-8 cm

Moderate: 8-10 cm

Severe: greater than 10 cm

M line: "perpendicularly from the posterior end of the H line to the pubococcygeal line, and represents the descent of the hiatus" (radiopaedia.org).

Normal: less than 2 cm

Mild: 2-4 cm

Moderate: 4-6 cm

Severe: greater than 6 cm

Once the patient has completed their defecography procedure, the radiologist will interpret the results. More than likely, if a patient is at the point where they were referred for this procedure, then the findings are probably out of normal ranges. If so, then potential conditions that may be diagnosed are dyskinetic puborectalis muscle syndrome, rectal intussusception (internal rectal prolapse), rectal and other type of prolapses, or descending perineum syndrome. These conditions may stem from lack of coordination between the pelvic floor muscles or from weakness from those pelvic floor muscles.

The defecography procedure is useful for a pelvic physical therapist because it gives me some insight on how to formulate my patient's plan of care, but it's not a requirement before I see a patient. There are plenty of things I can do to both gather my objective information and to treat my patients.

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References

Cleveland Clinic. (n.d.) Defecography. https://my.clevelandclinic.org/health/diseases/22333-defecography

Kim A. Y. (2011). How to interpret a functional or motility test - defecography. Journal of neurogastroenterology and motility, 17(4), 416–420. https://doi.org/10.5056/jnm.2011.17.4.416

Radiopaedia.org. (n.d.). H and M lines (pelvic floor). https://radiopaedia.org/articles/h-and-m-lines-pelvic-floor?lang=us