MR defecating proctography is a dynamic study for evaluation of the pelvic floor and pelvic organ prolapse.
Phases
There are four phases of evaluation:
- rest
- squeeze
- strain (Valsalva)
- defecation/evacuation
Method of evaluation
Many variations in the techniques described below exist.
Patient preparation
Typically there is no specific patient preparation required.
Sequences
Axial, coronal and sagittal T2W sequences of the pelvis are acquired to assess for structural abnormalities of the endopelvic fascia, pelvic viscera and musculature.
The dynamic study is carried out by acquiring cine images in the sagittal plane with a steady state sequence. This is similar to the sequence used for cardiac imaging. The dynamic sequences are acquired during squeezing, straining and evacuation. Prior to the evacuation sequence, 100-150 mL of ultrasound gel is instilled per rectum. Ultrasound gel is used as it is easy to acquire, manipulate into syringes, and is clearly seen on the cine sequences.
Endopelvic fascial defects
On the static images, as well as abnormalities involving the pelvic organs, signs of defects of the endopelvic fascia and levator muscle should be sought. These include the drooping moustache sign, saddlebag bladder sign, and chevron sign.
Measurements
After the acquisition of the appropriate images, the following lines are drawn and measurements are taken for evaluation and assessment of the outcome of this study.
- pubococcygeal line: a line joining the inferior aspect of the pubic symphysis to the final coccygeal joint, with perpendicular lines drawn to this line from organ specific reference points in the anterior, middle and posterior compartments; this line corresponds to the plane of the levator muscle
- mid-public line: this line, also known as the MPL, is drawn along the axis of the pubic symphysis and then perpendicular lines are drawn from the organ-specific reference points in the same manner as the PCL; this line is said to correspond anatomically to the hymenal opening
- H line: from the pubic symphysis to the posterior aspect of the anorectal junction, and corresponds to the AP diameter of the hiatus
- M line: drawn perpendicular from the PCL to the posterior end of the H line, and corresponds to pelvic hiatal descent during evacuation
These measurements should be used cautiously in men since they are not validated 4.
Abnormalities to assess
- pelvic floor descent
- bladder base descent (cystocele)
- vaginal vault descent
- rectocele
- intussusception
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