MR Defecography is a non-invasive imaging test that uses magnetic resonance imaging (MRI) to assess the function of the pelvic floor muscles and rectum. This procedure provides physicians with detailed, dynamic images of the pelvic anatomy as it moves during a simulated bowel movement. Unlike a standard, static MRI, this functional study evaluates the complex coordination required for defecation, offering a clear view of pelvic organ interaction without using ionizing radiation.
Purpose of the Procedure
Physicians may recommend this test when a patient experiences persistent symptoms that suggest a functional or structural issue within the pelvic region. Common complaints leading to an MR defecography include chronic constipation, fecal incontinence, a persistent feeling of being unable to completely empty the bowel, or pressure and pain in the pelvis. These symptoms can be indicative of underlying conditions that affect the support and operation of the pelvic organs.
The detailed images can reveal several specific medical conditions. A rectocele, where the rectum bulges into the vagina, can be clearly identified. An enterocele, which is a protrusion of the small intestine, or a sigmoidocele, involving the sigmoid colon, can also be visualized as they press into other structures. The test is also effective in diagnosing pelvic organ prolapse, a condition where pelvic organs like the bladder or rectum descend from their normal position. Another condition it can identify is anismus, where the pelvic floor muscles fail to relax properly to allow for a bowel movement.
The Patient Experience
Preparation is straightforward and begins at home. Patients may be asked to follow specific dietary instructions or fast for a few hours before the appointment. To ensure the bowel is clear for optimal imaging, patients are often provided with an enema kit to use prior to leaving for the facility.
Upon arrival, the process will be explained by the clinical team. A part of the procedure involves the introduction of a gel into the rectum. This gel, which has a consistency similar to stool, allows the radiologist to visualize the rectum’s function during evacuation. For female patients, a similar gel may be placed in the vagina to help delineate the pelvic organs more clearly. The patient then lies down on a special table that slides into the MRI machine.
Inside the MRI scanner, the patient will be positioned on a device that functions like a commode. The technologist communicates through an intercom system, guiding the patient through a series of commands at different stages of the scan. These instructions will include “rest,” “squeeze” the pelvic muscles, “bear down” as if having a bowel movement, and finally, “evacuate” the gel. The MRI machine will produce loud noises, and patients are given headphones to minimize the sound.
Immediately following the test, patients can go home and resume their normal daily activities without any downtime. The contrast gel is expelled during the procedure or will pass shortly after. There are no lasting effects from the scan itself.
Interpreting the Results
After the scan is complete, a radiologist analyzes the dynamic sequences. The radiologist examines the position and movement of the pelvic organs, including the bladder, vagina, rectum, and small bowel, during each phase of the test—rest, squeeze, strain, and evacuation. They look for any abnormal descent or protrusion of these organs, which would indicate prolapse or other structural issues.
The analysis includes measuring specific anatomical markers, such as the anorectal angle, to see how it changes during the process. These measurements help quantify the degree of pelvic floor relaxation or contraction. These detailed observations are compiled into a comprehensive report for the patient’s referring physician, who will discuss the findings and formulate a treatment plan.
Comparison with Other Diagnostic Tests
MR defecography is often compared to conventional fluoroscopic defecography, which uses X-rays. The primary advantage of the MRI-based method is its superior detail of soft tissues. This allows for a thorough assessment of the muscles, ligaments, and organs within the pelvis without exposing the patient to ionizing radiation.
While fluoroscopic defecography remains a useful test, it is less effective at visualizing the interactions between different pelvic compartments simultaneously. A study has shown that while fluoroscopy may be better at detecting certain conditions like rectoceles and rectal prolapse due to the upright patient positioning, MRI offers a more comprehensive view of multi-organ prolapse. The choice between the two often depends on the specific clinical question.