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What is MR Defecography?
Magnetic Resonance Defecography (MRD), an integral part of the evaluation of constipation and fecal incontinence, employs MR technology to delineate both the anatomy and function of pelvic floor structures.
MRD evaluates all compartments of the pelvic floor in contrast to standard defecography which can only visualize the posterior pelvic compartment (rectum and anus). This technique also allows the central compartment (vagina, cervix, uterus) along with the anterior compartment (bladder and urethra) to be evaluated. Incomplete evaluation of the entire pelvic floor is a leading cause for failure of corrective surgery. MRD affords one test to obtain all the information needed for collaborative efforts by the colorectal surgeon, urogynecologist, gynecologist and urologist in repair of these complex problems.
In patients with symptoms of obstructed defecation, MRD can identify abnormalities (e.g., small bowel enterocele, sigmoid enterocele, rectocele or uterine prolapse) causing pressure on the rectum and subsequent feeling of pelvic pressure. It can also establish stool trapping in a rectocele, an important criterion in surgical decision making. MRD can also confirm paradoxical motion of the external anal spincter during attempted defecation (anismus).
In patients with fecal incontinence, MRD can identify perineal descent and internal rectal prolapse. In patients with bona fide (external) rectal prolapse, MRD is critical in identification of any abnormality impinging on the cul– de– sac aggravating the rectal prolapse (e.g., small bowel or sigmoid enterocele, rectocele).
This will allow the proper surgery to be performed for both the rectal prolapse and any associated central or anterior pathology. MRD can also identify sphincter injury secondary to childbirth or prior surgery.
MRD also allows for the exclusion of any occult abscess or fistulae, hernia or tumors of the anus and rectum.
In contrast to standard defecography, no ionizing radiation is utilized and no bowel preparation is needed. This enhances overall patient compliance and satisfaction.
How should the patient prepare for the procedure?
Since MRI uses a strong magnetic field, patients will be asked if they have any metallic objects in their body. Any patient with a cardiac pacemaker, old pacemaker wires, an implantable defibrillator, cochlear implant, neurostimulator, or non-MRI compatible aneurysm clip is not a candidate for MRI. Also, any patient with shrapnel in their body or a metallic foreign body in or around their eyes should not undergo an MRI study. In most cases, cardiac stents, artificial heart valves, prosthetic joints, and surgical staples, plates, pins and screws pose no risk during MRI if they have been in place for more than four to six weeks and are MRI compatible. (Patients should check the MRI compatibility of these devices with their physician prior to having an MRI.) Dental fillings and braces are not affected by the magnetic field.
Female patients should not have an MRI during the first trimester of pregnancy. If there is a chance of pregnancy, a pregnancy test should be performed prior to the exam. MRI can be performed in the second and third trimesters with prior physician approval. Some patients who undergo MRI may feel claustrophobic. If this is the case, a sedative may be administered to help the patient through the exam.