Magnetic Resonance Imaging

The development of fast-scanning magnetic resonance imaging (MRI) techniques has improved our ability to describe and quantify anatomical changes that may cause pelvic floor relaxation. Yang et al.3 were the first to popularize dynamic fast MRI for the evaluation of pelvic organ prolapse. Since then, other investigators have shown that MRI is more sensitive than physical examination for defining pelvic prolapse.4,5 Whereas some advocate the use of contrast opacification of the bladder, vagina, and rectum, others have shown that the vagina, rectum, bladder, urethra, and peritoneum are adequately visualized without any contrast administration. By avoiding instrumentation of the vagina or urethra, iatrogenic alteration of the anatomy is minimized.

Magnetic resonance imaging, however, can noninva-sively survey the entire pelvis. The excellent differentiation among soft tissues and fluid-filled viscera provides visualization of the musculofascial support structures of the pelvic organs. Our group and others have previously demonstrated the clinical utility of MRI for evaluating bladder neck and urethral anatomy, and the utility of dynamic MRI for assessing pelvic floor descent and genital prolapse, and development of dynamic rapid sequencing has greatly improved the diagnostic utility of MRI by allowing exquisite anatomical detail during brief breath-holds (Figures 3-3.1 and 3-3.2). Magnetic resonance

Utites Prolaps

Figure 3-3.1. Magnetic resonance image of the pelvis demonstrating significant cys-tocele with descent of bladder base and trigone well below pubic symphysis.

Figure 3-3.3. Magnetic resonance image of urethral diverticulum (see arrow).

Figure 3-3.1. Magnetic resonance image of the pelvis demonstrating significant cys-tocele with descent of bladder base and trigone well below pubic symphysis.

imaging has become our choice for imaging patients with suspect urethral diverticula (Figure 3-3.3).

There are, however, several limitations of this technique. Defining normal values is difficult, because it would be quite expensive to perform dynamic MRIs on nulliparous women without any urologic complaints. Our choice for the nonprolapse group (normal patients) included patients in whom we desired an imaging study to evaluate pathol-

View Fibroids From Pelvic Exam
Figure 3-3.2. Magnetic resonance image demonstrating a well-supported bladder (white on T2-weighted study), but significant enterocele behind it.

ogy other than pelvic prolapse, such as recurrent infections, pelvic pain, and urethral pain. Another limitation is that a collapsed rectocele may not be visualized because of competition among prolapsing pelvic organs for limited introital space. In fact, physical examination has been shown to be slightly more accurate in demonstrating rec-tocele formation than MRI. Additionally, the study must be performed supine, simply because there are no upright MRI machines available at this time. However, dynamic MRI with relaxing and straining views has been shown to clearly demonstrate organ prolapse during straining in the supine position. An erect MRI is the next logical advancement. Finally, claustrophobic patients and those with cardiac pacemakers cannot go into the enclosed magnet. Despite these limitations, dynamic MRI has become the study of choice at our institution for evaluating high-grade pelvic prolapse and pelvic floor relaxation. Because this is a new technique, a standardized system for describing and quantifying organ prolapse and pelvic floor relaxation is important.

Magnetic resonance imaging findings were compared to physical examination and intraoperative findings. HASTE-sequence MRI was more accurate than physical examination in identifying cystoceles, enteroceles, vault prolapse, and pelvic organ pathology such as uterine fibroids, ure-thral diverticula, ovarian cysts, and Nabothian and Bartholin's gland cysts.5 Comiter et al.6 found that with dynamic MRI, surgical planning was altered in more than 30% of cases, most often because of occult enterocele not appreciated on physical examination.

In patients with severe prolapse, especially with renal insufficiency, the surgeon must rule out obstructive hydroureteronephrosis. This may be accomplished by magnetic resonance urogram, adding only minimally to overall examination time, and with no additional morbidity. Mag netic resonance imaging may also be useful for the radiographic evaluation of stress incontinence. Hypermobility of the proximal urethra and bladder neck descent are important pathological features in the diagnosis of genuine stress urinary incontinence.7'8 Measurement data on dynamic MRI for the bladder neck position and the extension of cystocele at maximal pelvic strain are comparable with lateral cystourethrogram data.9

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