Dynamic MRI of the Pelvic Floor
Pelvic floor dysfunction annually affects nearly 300,000 to 400,000 women severely enough to necessitate surgery. Dysfunction of the pelvic floor may manifest as prolapse, incontinence, pelvic pain, or constipation.
The pelvic floor can be divided into 3 compartments: the anterior compartment, which contains the bladder and urethra; the middle compartment, which contains the vagina, cervix, and uterus; and the posterior compartment, which contains the rectum. All 3 compartments are supported by a complex network of muscles and fascia that form the urogenital diaphragm, or the pelvic floor. Damage to ≥1 of these myofascial elements can lead to individual or multiple organ prolapse, and overall laxity and stretching or tearing can lead to generalized pelvic floor relaxation.
Diagnosis and grading of pelvic floor dysfunction has previously been performed with physical examination and radiographic imaging, such as voiding cystourethrography, evacuation proctography, cystocolpoproctography, and peritoneography. However, the development of fast MRI sequences has allowed for the quick evaluation of pelvic organ prolapse and pelvic floor relaxation with increased patient comfort, decreased complexity, and decreased invasiveness and radiation exposure. The intrinsic soft tissue contrast capability of MRI allows for detailed visualization of the pelvic floor, and the faster techniques now allow for dynamic evaluation of pelvic support structures. Studies have shown that dynamic MRI has greater sensitivity than physical examination and has led to changes in the initial surgical plan in 41% of patients. It has become clear that MRI has an important role in the preoperative planning in patients with pelvic floor dysfunction.[42,43]
Currently, no universally accepted radiologic criteria for assessing pelvic floor dysfunction exist; however, the most widely accepted criteria involve organ movement below the pubococcygeal line (PCL), which extends from the inferior margin of the symphysis pubis to midway between the frst and second coccygeal segments. A line that extends from the lowermost aspect of the symphysis pubis to the puborectalis muscle forms the puborectalis hiatus. In the normal patient, the puborectalis hiatus is <6 cm and does not descend >2 cm below the PCL. The upper urethra, urethrovesical junction, bladder, upper vagina, uterus, small bowel, sigmoid colon, mesenteric fat, and rectum should all be above the hiatus. Staging of any prolapse is done in 2-cm increments below the puborectalis hiatus. Small is 0 to 2 cm below, moderate is 2 to 4 cm, and a large prolapse extends >4 cm below this line.
For optimal MRI evaluation in the sagittal plane, the patient is placed in the supine position. Static images are frst obtained, with subsequent series of images performed during resting and straining in the midsagittal plane. Selected midline sagittal T2W images at rest and on the Valsalva maneuver and/or sagittal 2D GRE images in real-time at rest and on Valsalva are used to assess the degree of pelvic floor descent and pelvic organ prolapse (Figure 15).[42,43] Some authors advocate the use of intraluminal contrast, but this is not used routinely at our institution.
Appl Radiol. 2008;37(1):9-24. © 2008 Anderson Publishing, Ltd.
Cite this: Imaging the Female Pelvis: When Should MRI be Considered? - Medscape - Jan 01, 2008.