Dynamic MR imaging of outlet obstruction

The outlet obstruction syndrome encompasses all pelvic floor abnormalities which are responsible for an incomplete evacuation of fecal contents from the rectum. It has been estimated that outlet obstruction may be observed in half of constipated patients. A detailed clinical examination still represents the cornerstone of the diagnosis of these patients. However, there is general agreement that a reliable evaluation of the different pelvic floor abnormalities and the treatment decision highly depend on the imaging assessment. Traditionally, conventional defecography has played an important role in the radiological assessment of these patients but the technique is limited by its projectional nature and its inability to detect soft-tissue structures. Dynamic pelvic MR imaging using either closed-configuration or open-configuration MR systems is a rapidly evolving technique which has been gaining increased interest over the last years. The free selection of imaging planes, the good temporal resolution, and the excellent soft-tissue contrast have transformed this method into the preferred imaging modality in the evaluation of patients with pelvic floor dysfunction including rectocele, enterocele, internal rectal prolapse, and anismus.