MR Defecography

MR Defecography

Aids to Interpretation

  • Pubococcygeal line (PCL): connects inferior aspect of symphysis pubis to last coccygeal joint
  • Anorectal juction (ARJ): crosspoint of line along posterior border of the rectum and line along central axis of anal canal
  • Anorectal angle (ARA): Angle beween the two lines used to define the ARJ At rest base of bladder, upper third of vagina and peritoneal cavity should be above PCL. ARJ within 3cm below PCL.
  • At squeeze elevation of pelvic organs and ARA should reduce by at least 15 to 20o
  • At strain and defecation mild descent of pelvic organs (<2cm) expected. ARA typically increased by 15-20o more than rest

Measurements

Abdominal MR Defecography Measurements Rest
Rest
MR Defecography Measurements Squeeze

Normal Study

Rest Squeeze
Strain Defecation

 

Definition

Abnormality Small Moderate Large
Rectal descent < 3 cm* (normal) 3-6 cm* > 6 cm*
Bladder descent < 3 cm* (normal up to 1 cm) 3-6 cm* > 6 cm*
Vagina descent < 3 cm* 3-6 cm* > 6 cm*
Rectocele size < 2 cm (normal) 2-4 cm* > 4 cm*
Enterocele < 3 cm* 3-6 cm* > 6 cm*

 

Examples of Pathology

Abnormal Rectal Descent

  • Greater than 3 cm descent of the anorectal junction below the PCL
  • Decreased raising of the rectum at maximal contraction

Rectocele

  • Anterior bulge of rectum beyond the expected margin of the anterior wall
  • Abnormal if exceeds 2 cm

Rectal Intussusception

  • Invagination of rectal wall
  • Anterior, posterior or circumferential
  • Mucosal or full thickness
  • Intrarectal, intraanal or extraanal

Rectal Prolapse

  • Extraanal intussusception
  • Mucosal or full thickness

Anismus

  • Lack of relaxation of puborectalis during strain and defecation with lack of normal pelvic floor descent
  • May be associated anterior rectocele

Enterocele

  • Inferior protrusion of peritoneum between rectum and vagina
  • May contain fat, small bowel or sigmoid colon

Cystocele

  • Inferior protrusion of the bladder below the PCL
  • Abnormal if exceeds 1 cm

Utero-vaginal Prolapse

Utero-vaginal Prolapse
  • Uterine descent into the vagina
  • Complete prolapse results in the uterus falling outside

References

  1. Lalwani N, Moshiri M, Lee JH, Bhargava P, Dighe MK. Magnetic resonance imaging of pelvic floor dysfunction. Radiol. Clin. North Am. 2013 Nov;51(6):1127–39.
  2. Flusberg M, Sahni VA, Erturk SM, Mortele KJ. Dynamic MR defecography: assessment of the usefulness of the defecation phase. AJR Am. J. Roentgenol. 2011 Apr;196(4):W394–399.
  3. Mortele KJ, Fairhurst J. Dynamic MR defecography of the posterior compartment: Indications, techniques and MRI features. Eur. J. Radiol. 2007 Mar;61(3):462–72.
  4. Roos JE, Weishaupt D, Wildermuth S, Willmann JK, Marincek B, Hilfiker PR. Experience of 4 years with open MR defecography: pictorial review of anorectal anatomy and disease. Radiogr. Rev. Publ. Radiol. Soc. N. Am. Inc. 2002 Aug;22(4):817–3