Defecorgaphy MRI vs Conventional: Pros and Cons

Defecography has become a standard tool for evaluation of the posterior compartment of the pelvic floor. Initially, conventional X-ray defecography provided clinicians with important information about the anatomic and functional status of the posterior compartment and the presence of various conditions including rectocele, prolapse, intussusception, perineal descent, and relaxation difficulties of the puborectalis. This test is performed in the sitting position, which is the more physiologic position for defecation and provides real-time imaging during the defecation attempt. The use of a contrasting agent enables the visualization of the rectum and the evacuation process. The downside to this evaluation method is the need for opacification of the rectum, the use of ionizing radiation and the lack of imaging of the anterior compartments. X-ray defecography is a readily available cost-effective method for evaluation of the posterior pelvic compartment and diagnosis of defecatory disorders. The addition of the dynamic MRI defecography to the armamentarium of physicians who treat pelvic floor disorders has provided a tri-compartment view of this complex space to each of the teams contributing to the multidisciplinary care of the often-intertwined disorders of the pelvic floor. This view can be incredibly relevant when patients have concomitant pathology or prolapse. MRI provides soft tissue detail not available with standard X-ray images and can help the treating team better plan for surgical intervention and can be particularly important for patients suffering from functional problems after surgical procedures. A common criticism, however, is that MRI is not done in the physiologic position. The patient is typically in the lying position and defecation in the sitting position is not simulated, thereby potentially limiting the evaluation of prolapse. In addition, there is a significant expense associated with MRI compared to X-ray.

When evaluating patients with posterior compartment complaints of difficult evacuation or prolapse, in the absence of anterior compartment complaints or prolapse, X-ray defecography may provide the necessary information about the patient’s function in the physiologic position. If a patient has anterior compartment complaints, prolapse, or history of prior surgery, the addition of a dynamic MRI may prove useful. I believe these tests are complementary rather than exclusive.