MR imaging of pelvic floor relaxation

Anatomy

The pelvic floor can be divided into three compartments: (1) the anterior compartment, which contains the bladder and urethra, (2) the middle compartment, which contains the vagina, cervix, and uterus, and (3) the posterior compartment, which contains the rectum.

All three compartments are supported by a remarkable collection of fascia and muscle that forms the urogenital diaphragm, or pelvic floor. The muscles that provide the major support of the pelvic organs are two components of the levator

Imaging techniques

For most patients with mild to moderate stress incontinence and pelvic floor relaxation, the combination of physical examination findings and urodynamic pressure readings is diagnostic and no further imaging is required. For patients with severe urinary or fecal incontinence believed to be multifactorial, multiple compartment involvement, or failed prior surgery, imaging can be valuable. Several techniques can be used to evaluate the pelvic organs, including voiding cystourethrography (with or

MR technique

Obtaining high-quality, useful images requires careful attention to patient preparation and examination technique. Just before imaging, the patient is asked to void, which prevents a distended bladder from distorting adjacent anatomy. If the examination is focused on the posterior compartment, 60 cc of ultrasound gel is placed in the rectum using a small catheter. A multicoil array, either pelvis or torso, is wrapped around the inferior portion of the pelvis and the patient is placed in the

MR anatomy

On sagittal images, the pubococcygeal line should be drawn between the last joint of the coccyx and the inferiormost aspect of the symphysis. Urologists and gynecologists use this line as an indicator of the pelvic floor. In early work, Yang et al [17] used gradient echo images to define maximal normal descent of the bladder base (1 cm below), vagina (1 cm above), and rectum (2.5 cm below) with respect to the pubococcygeal line. In practical terms, descent of the bladder or vagina more than 1

Anterior compartment pathology

Women who present with severe stress incontinence refractory to behavioral, drug, and surgical therapy are good candidates for MR imaging. At strain, the bladder neck extends well below the pubococcygeal line. Because of the strong attachments anteriorly, the posterior wall of the bladder rotates posteriorly and inferiorly, impressing on the vaginal wall. The H and M lines are increased in length. During bladder descent, the urethra sometimes rotates clockwise. This kinking of the urethra at

Middle compartment pathology

Descent of the reproductive organs is almost always associated with cystocele formation because of the shared fascial supports. Gynecologists grade descent by comparing organ location with bony and soft tissue landmarks. On sagittal MR imaging, descent of the uterus in addition to the vagina and cervix usually indicates rupture of the cardinal or uterosacral ligaments. It is not uncommon to identify a uterine fibroid that prevents descent of the uterus and masks the true degree of pelvic floor

Posterior compartment pathology

A rectocele or enterocele can occur alone or in combination with other pelvic floor defects to form global pelvic floor relaxation. Many of these patients previously underwent hysterectomies that left them with thinned or torn fascia. On sagittal MR imaging, a rectocele is identified by anterior bulging of the rectal wall, usually into the pouch of Douglas. Enteroceles occur when the rectovaginal fascia is torn, which allows small bowel loops to descend more than 2 cm, again into the

Global pelvic floor relaxation

In severe cases, there is significant descent of the contents of all three compartments of the pelvic floor below the pubococcygeal line [23]. The levator plate is nearly vertical, and there is extreme elongation of the H and M lines (Fig. 11). On axial images there is nearly always increased hiatal width and ballooning of the iliococcygeus. This latter finding and any associated perineal hernias may be identified best on coronal images. Repair of these patients is complex and often includes

Summary

The wide variety of available surface coils, pulse sequences, and post-processing techniques make MR imaging a useful clinical and research tool for evaluation of pelvic floor relaxation. Cases of isolated cystocele do not require imaging; however, in cases in which multiple compartments of the pelvis are involved or the patient has failed prior surgery, MR imaging should be considered for preoperative planning.