MRI DEFECOGRAPHY

MRI Defecography is a specialized magnetic resonance imaging technique used to evaluate pelvic floor anatomy and function during rest and defecation. It provides dynamic, multiplanar images without radiation exposure, making it a preferred method for assessing pelvic floor disorders. Unlike conventional fluoroscopic defecography, MRI offers superior soft tissue detail, allowing visualization of the pelvic organs, muscles, and supporting structures during different phases of defecation. This test is particularly valuable in patients with symptoms of constipation, fecal incontinence, pelvic organ prolapse, or complex pelvic floor dysfunction.

Purpose of MRI Defecography

1. Assessment of pelvic floor disorders

• Identifies structural and functional abnormalities.
• Evaluates pelvic organ descent during straining or defecation.

2. Evaluation of constipation causes

• Detects outlet obstruction, rectocele, or intussusception.

3. Investigation of incontinence

• Reveals sphincter weakness or abnormal pelvic floor relaxation.

4. Surgical planning

• Provides detailed preoperative mapping for pelvic floor reconstruction or repair.

5. Post-treatment follow-up

• Assesses the outcome of surgical or physiotherapy interventions.

Common Clinical Indications

• Chronic constipation unresponsive to conservative therapy.
• Symptoms of incomplete evacuation.
• Fecal incontinence.
• Suspected pelvic organ prolapse.
• Post-surgical recurrence of pelvic floor disorders.
• Chronic pelvic pain with suspected muscular dysfunction.

Procedure for MRI Defecography

Before the scan

• The patient is counseled about the procedure, including the need for straining and defecation during the scan.
• A bowel preparation may be recommended to ensure cleanliness.
• No metallic objects should be worn.
• Patients should inform the radiology team about pregnancy, implants, or prior surgeries.

During the scan

• The patient lies in a supine position inside the MRI scanner, although some centers use open or seated MRI systems for a more natural defecation posture.
• A rectal catheter is inserted, and a gel-like contrast material (MRI-compatible) is instilled into the rectum to simulate stool.
• In female patients, vaginal contrast gel may also be used to assess vaginal wall support.
• Imaging is performed at rest, during pelvic floor contraction, straining, and evacuation phases.
• Multiple sequences are obtained, including static and dynamic cine MRI.

After the scan

• The patient is cleaned and assisted as needed.
• The radiologist analyzes the images to measure pelvic organ movement and identify abnormalities.

MRI Sequences Used in Defecography

Static sequences

• T2-weighted sagittal and axial images for baseline anatomy.
• Coronal views for assessing lateral pelvic floor structures.

Dynamic sequences

• Cine MRI using fast imaging sequences during rest, squeeze, strain, and evacuation.
• Images are recorded in real time to observe pelvic organ descent and movement.

Key Measurements and Parameters

Pubococcygeal line (PCL)

• Baseline reference line from the pubic symphysis to the coccyx.

H line

• Measures the anteroposterior dimension of the levator hiatus.

M line

• Measures the vertical descent of the levator hiatus below the PCL.

Organ descent

• Quantified for bladder base, vaginal apex, and anorectal junction.

Findings in MRI Defecography

Rectocele

• Anterior bulging of the rectal wall into the vagina.
• Size is measured, and retention of contrast after evacuation is noted.

Intussusception

• Telescoping of the rectal wall into the anal canal during straining.

Enterocele

• Herniation of small bowel loops into the rectovaginal or rectovesical space.

Pelvic organ prolapse

• Bladder prolapse (cystocele), uterine or vaginal vault prolapse, and rectal prolapse can be identified.

Anismus

• Inappropriate contraction or failure of relaxation of the pelvic floor muscles during defecation.

Levator ani injury

• Muscle defects or asymmetry.

Combined compartment prolapse

• Simultaneous descent of anterior, middle, and posterior compartments.

Advantages of MRI Defecography

• No radiation exposure.
• Superior visualization of pelvic muscles, fascia, and ligaments.
• Ability to assess all three compartments of the pelvis simultaneously.
• Differentiates structural and functional causes of symptoms.
• Allows correlation of findings with other pelvic floor imaging modalities.

Limitations

• Supine position in most scanners may not reflect natural defecation dynamics.
• Limited availability of open MRI systems for seated defecography.
• Longer examination time compared to conventional methods.
• Higher cost compared to fluoroscopic defecography.
• Requires patient cooperation and ability to follow instructions.

Applications in Clinical Practice

In constipation

• Differentiates slow transit constipation from outlet obstruction.
• Identifies rectocele, anismus, or intussusception.

In incontinence

• Detects pelvic floor laxity, sphincter defects, or excessive organ descent.

In pelvic organ prolapse

• Provides detailed anatomical information for surgical repair planning.

In chronic pelvic pain

• Helps identify underlying muscular spasm or structural defects.

Preparation Tips for Patients

• Wear comfortable, loose clothing free of metal components.
• Empty bladder before the procedure unless instructed otherwise.
• Follow any specific dietary or bowel preparation instructions.
• Practice pelvic floor exercises beforehand to understand instructions for contraction and relaxation.

Role in Multidisciplinary Management

MRI Defecography is often used alongside urogynecological and colorectal evaluation to provide a complete pelvic floor assessment. Surgeons, physiotherapists, and gastroenterologists can use the findings to develop targeted treatment plans. Post-treatment MRI can document improvement and guide rehabilitation strategies.

Conclusion

MRI Defecography is an advanced, dynamic imaging tool that offers a comprehensive evaluation of pelvic floor anatomy and function. It plays a critical role in diagnosing complex defecatory disorders, incontinence, and pelvic organ prolapse by providing detailed visualization of both structural and functional abnormalities. Its ability to assess all three compartments of the pelvis in a single session, without radiation, makes it an invaluable tool for diagnosis and treatment planning. While limitations exist regarding positioning and availability, its diagnostic accuracy and clinical utility make MRI Defecography a preferred choice in many specialized centers.