Functional disorders of the ano-rectal compartment of the pelvic floor: clinical and diagnostic value of dynamic MRI

The obstructed defecation syndrome is the main functional disorder of the posterior or ano-rectal pelvic floor compartment. Different mechanical and functional rectal disorders may cause this syndrome, including rectocele, rectal invagination, rectal prolapse, and pubo-rectalis muscle dyskinesia. Since pelvic floor muscles and fasciae act as a unique functional entity, dysfunctions of the posterior compartment are usually associated to variable dysfunctions of the anterior and middle urogenital compartments as well. Over 50% of postmenopause women are affected by severe symptoms due to pelvic floor disorders, with frequent need of surgical invasive treatments. Both diagnosis of the specific ano-rectal dysfunction and identification of all possible associated disorders are mandatory for an effective surgical or conservative treatment. Currently, dynamic MRI provides an excellent morphological and functional display of the pelvic floor like no other imaging modality. Pros and cons of posterior pelvic floor MRI, different evaluation techniques, reference lines and grading systems together with the main imaging findings will be discussed and illustrated.