HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Figures Only Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Law, Y. M. Articles by Fielding, J. R. Search for Related Content PubMed PubMed Citation Articles by Law, Y. M. Articles by Fielding, J. R. Social Bookmarking                      What's this? Hotlight (NEW!) What's Hotlight?

MRI of Pelvic Floor Dysfunction: Review

¹ Department of Diagnostic Radiology, Singapore General Hospital, Outram Rd., Singapore 169608, Republic of Singapore.
² Department of Radiology, The University of North Carolina at Chapel Hill, Chapel Hill, NC.

Received April 24, 2008; accepted after revision June 17, 2008.

 
Address correspondence to Y. M. Law (law.yan.mee{at}sgh.com.sg).

Abstract

Top Abstract Introduction Anatomy Imaging Imaging Technique Interpretation of MRI Findings Urinary Incontinence and... Middle Compartment Prolapse Posterior Compartment Prolapse Summary References

 
OBJECTIVE

The purpose of this article is to review the anatomy and etiology of pelvic floor weakness in women and to discuss the role of MRI in the assessment of female pelvic floor dysfunction.

CONCLUSION

In women with pelvic floor weakness, pelvic MRI, with its superior soft-tissue contrast resolution, allows direct visualization of the pelvic organs and their supportive structures in a single noninvasive examination. By providing useful and valuable information on the extent and severity of pelvic organ prolapse, MRI plays a valuable role in preoperative planning of complex cases.

Keywords: cystocele • MRI • pelvic floor dysfunction • rectocele

Introduction

Top Abstract Introduction Anatomy Imaging Imaging Technique Interpretation of MRI Findings Urinary Incontinence and... Middle Compartment Prolapse Posterior Compartment Prolapse Summary References

 
Weakening of the female pelvic floor is a prevalent and debilitating disorder. It results in abnormal descent of the urinary bladder, the uterovaginal vault, and the rectum, resulting in urinary continence, fecal incontinence, and pelvic organ prolapse. Pelvic floor weakening affects approximately 50% of women older than 50 years at a direct annual cost of $12 billion [1, 2]. It is a major health issue in older women, as shown by the 11.1% lifetime risk of undergoing a single operation for pelvic organ prolapse and urinary incontinence, as well as the large proportion of reoperations [3].

Pelvic floor weakness has many complex causes. The risk factors for pelvic floor dysfunction include pregnancy, multiparity, advanced age, menopause, obesity, connective tissue disorders, smoking, chronic obstructive pulmonary disease, and any other factors that result in a chronic rise in intraabdominal pressure. A consensus conference statement from the National Institutes of Health concluded that age, sex, and vaginal parity are established risk factors [4]. Although epidemiologic evidence supports the relation between vaginal delivery and pelvic floor dysfunction [5], not all women who undergo vaginal delivery develop pelvic floor dysfunction [6], and not all nulliparous women are free from pelvic floor dysfunction [7]. Data and electromyographic studies also suggest that vaginal delivery causes neuromuscular damage to the pelvic floor well before the onset of pelvic floor dysfunction [8]. The support structures of the female pelvis consist of a complex network of pelvic muscles, fascia, and ligaments. Weakness of the pelvic musculature, ligaments, and fascia support result in abnormal descent of the pelvic floor organs and debilitating symptoms related to urinary or bowel incontinence, sexual dysfunction, and pelvic organ prolapse.

Anatomy

Top Abstract Introduction Anatomy Imaging Imaging Technique Interpretation of MRI Findings Urinary Incontinence and... Middle Compartment Prolapse Posterior Compartment Prolapse Summary References

 
The pelvic floor is divided into three compartments (Fig. 1A, 1B, 1C). The anterior compartment contains the urinary bladder and the urethra; the middle compartment contains the uterus, cervix, and vagina; and the posterior compartment contains the rectum. The support for these structures arises from the attachment of the muscles, fascia, and ligaments to the bony pelvis. MRI allows visualization of all three compartments and is extremely useful in assessing women who have symptoms of multicompartment prolapse before complex pelvic floor surgery is undertaken. The vagina, being the middle viscera and from its lateral attachments to the pelvic side walls via the ligaments, is the middle divider that determines the nature of any pelvic organ prolapse.

View larger version (28K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1A —Anatomy of the pelvic floor in women. Sagittal (A) and axial (B and C) line drawings show pubococcygeus and iliococcygeus muscles that are major component of levator ani muscles. Pubococcygeal line is drawn from most inferior portion of pubic symphysis to last horizontal sacrococcygeal line on midsagittal MR image. In contrast to what is shown on A, anococcygeal raphe, also known as levator plate, is usually parallel to pubococcygeal in normal subjects. (Reprinted with permission from Cardozo L. Urogynecology. New York, NY: Churchill-Livingstone, 1997:325–326 [41])

View larger version (48K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1B —Anatomy of the pelvic floor in women. Sagittal (A) and axial (B and C) line drawings show pubococcygeus and iliococcygeus muscles that are major component of levator ani muscles. Pubococcygeal line is drawn from most inferior portion of pubic symphysis to last horizontal sacrococcygeal line on midsagittal MR image. In contrast to what is shown on A, anococcygeal raphe, also known as levator plate, is usually parallel to pubococcygeal in normal subjects. (Reprinted with permission from Cardozo L. Urogynecology. New York, NY: Churchill-Livingstone, 1997:325–326 [41])

View larger version (35K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1C —Anatomy of the pelvic floor in women. Sagittal (A) and axial (B and C) line drawings show pubococcygeus and iliococcygeus muscles that are major component of levator ani muscles. Pubococcygeal line is drawn from most inferior portion of pubic symphysis to last horizontal sacrococcygeal line on midsagittal MR image. In contrast to what is shown on A, anococcygeal raphe, also known as levator plate, is usually parallel to pubococcygeal in normal subjects. (Reprinted with permission from Cardozo L. Urogynecology. New York, NY: Churchill-Livingstone, 1997:325–326 [41])

The levator ani muscles lie deep in relation to the endopelvic fascia. The two components of the levator ani that provide the major support to the pelvic organs are the puborectalis and the iliococcygeus muscles. The puborectalis forms a sling around the rectum and plays an important role in apposing the orifices of the pelvic floor as well as elevating the bladder neck and compressing it against the pubic symphysis. The iliococcygeus has a horizontal orientation, arises from the external anal sphincter, and fans out laterally, attaching to the arcus tendineus. Posteriorly and in the midline, the iliococcygeus condenses to form a firm raphe anterior to the coccyx known as the levator plate. The iliococcygeus muscle acts as an important physical barrier, preventing posterior compartment prolapse. The muscles of the pelvic floor and levator plate are well visualized on MRI.

The perineal membrane lies inferior to the levator ani muscles and separates the vagina and rectum. It is a dense structure and is the point of insertion of five muscles: the deep transverse perineal muscle, the superficial muscles of the perineal membrane, the external urethral sphincter, the external anal sphincter, and the levator ani. The perineal body prevents expansion of the urogenital hiatus, which is the opening in the levator ani muscle groups through which the urethra, vagina, and rectum course; it is also the orifice through which pelvic organ prolapse occurs. The perineal membrane may be damaged during vaginal delivery via an episiotomy.

It is the weakness of these supporting muscles, fascia, and ligaments that results in pelvic floor relaxation. This weakness progresses with age and may be related to menopause and hypoestrogenemic states. Loss of support to the urinary bladder and the urethra results in prolapse of the urinary bladder and protrusion of the anterior vaginal wall, forming a cystocele, which may result in urinary incontinence. Weakness of the parametrium and paracolpium causes prolapse of the cervix and uterus, and weakness of the rectovaginal fascia results in prolapse of the rectum and protrusion of the posterior vaginal wall, forming a rectocele, and may result in fecal incontinence. Prolapse of the small bowel through the rectovaginal fascia results in an enterocele. In patients who have undergone a hysterectomy, prolapse of the vaginal apex can arise because of weakness of the paracolpium, resulting in apical prolapse.

Imaging

Top Abstract Introduction Anatomy Imaging Imaging Technique Interpretation of MRI Findings Urinary Incontinence and... Middle Compartment Prolapse Posterior Compartment Prolapse Summary References

 
In women with symptoms of pelvic floor weakness, physical examination is essential for diagnosing pelvic organ prolapse. Most patients with mild symptoms of pelvic floor weakness, such as mild urinary continence, may benefit from a thorough physical examination and urodynamic studies. In patients with moderate to severe symptoms, such as severe urinary incontinence, procidentia, fecal incontinence, or symptoms suggesting a complex pelvic floor disorder, physical examination may be inadequate, and imaging will be useful. Studies have reported poor sensitivity and specificity of physical examination in diagnosing various forms of pelvic floor dysfunction [10]. Several studies have also shown that patients with urinary incontinence have coexistent pelvic organ prolapse in the other two compartments that requires surgical repair [11–13]. Accurate assessment of all compartments of the pelvic floor is therefore essential in planning surgical reconstruction in order to minimize the risk of recurrence and repeated surgery.

Traditional imaging methods in assessment of pelvic floor weakness include urodynamics, voiding cystourethrography, ultrasonography of the bladder neck and anal sphincter, and fluoroscopic cystocolpodefecography. In the past decade, MRI has emerged as a competitor to these techniques in the assessment of pelvic floor dysfunction. Although MRI is not indicated for the routine assessment of all patients with mild symptoms of pelvic floor dysfunction, it is certainly an invaluable tool in preoperative planning because it provides detailed anatomic information and may alter the management of patients. In assessing the influence of MR defecography on surgical therapy in patients with fecal incontinence, Hetzer et al. [14] showed that findings on MRI led to a change of surgical therapy in 67% of patients in whom some form of surgery was required to treat fecal incontinence. In some centers, MRI is routinely used in preoperative planning before pelvic floor surgery [15].

In recent years, MRI has been shown to be effective in revealing pelvic floor dysfunction. It allows concomitant visualization of all three compartments of the pelvic floor and at the same time allows direct visualization of the pelvic support muscles and organs. With advances in technology, new machines and new sequences have allowed increased SNR as well as faster acquisition times. In most instances, dynamic MRI examination of the pelvic floor is performed with the patient in the supine or lateral decubitus position, which does not mimic the normal physiologic state. MRI defecography performed in a 0.5-T open MR system or fluoroscopic cystocolpodefecography, both of which are performed with the patient in the sitting position, more closely resemble the physiologic state. Although visibility of laxity in the pelvic floor in patients with pelvic floor dysfunction may be increased on sitting MRI compared with supine studies, Bertschinger et al. [16] compared sitting MR defecography with dynamic supine MRI and showed that sitting MR defecography is not superior to dynamic supine MRI for depiction of clinically relevant bladder descent and rectoceles. Similarly, the study by Fielding et al. [17] showed that although a greater degree of pelvic floor laxity was shown on MRI in the sitting position, it was not superior to standard supine MRI.

Moreover, in a 0.5-T open MRI system, one must contend with images of a lower SNR and soft-tissue resolution. MRI shows enteroceles with a high degree of accuracy when compared with physical examination and fluoroscopic cystodefecography [18, 19]. Other studies show that dynamic supine MRI and fluoroscopic defecography have similar detection rates for rectocele [20]. Another advantage of MRI is that it provides additional information about the contents of the enterocele, which may include small bowel, omentum, mesenteric fat, or large bowel. MRI allows better visualization than other techniques of the uterus, cervix, and rectovaginal space and hence increases the conspicuity of posterior compartment prolapse. Many different MRI techniques are described in the literature for imaging of the pelvic floor that may or may not require opacification of the pelvic organs [21–23]. The pelvic organs may be opacified by instilling ultrasonic gel into the vagina and rectum [23].

Imaging Technique

Top Abstract Introduction Anatomy Imaging Imaging Technique Interpretation of MRI Findings Urinary Incontinence and... Middle Compartment Prolapse Posterior Compartment Prolapse Summary References

 
In MRI of the pelvis, adequate patient preparation and a good technique with fast acquisition time are required to achieve maximum patient comfort and hence better patient compliance. The patient will be asked to void partially before the dynamic examination in order to prevent a distended urinary bladder from obscuring the pelvic structures and masking pelvic organ prolapse. Maintaining a small amount of urine in the urinary bladder improves visualization of the bladder and anterior vaginal wall prolapse. The examination is performed with a torso phased-array coil wrapped around the pelvis. Although use of an endovaginal coil may improve the spatial resolution of the fine supporting ligaments in the pelvis, it is invasive and may diminish patient acceptance and compliance [9]. The use of an endovaginal coil may distort the pelvic tissues in patients with a small pelvis. The field of view is small and often inadequate for visualization of the puborectalis. To improve visualization of the vagina and rectum, a small volume of intraluminal ultrasonic gel that has a hyperintense T2 signal may be instilled. Via a small-caliber catheter-tip syringe, 20 mL of gel may be instilled into the vagina and approximately 60–120 mL into the rectum. Although the dynamic MRI examination may be performed without endoluminal gel, doing so results in suboptimal straining that masks the degree of pelvic organ prolapse and results in inconspicuity of visceral descent.

Ultrafast, large-field-of-view, T2-weighted sequences such as single-shot fast spin-echo (SSFSE, GE Healthcare scanners) or half-Fourier acquisition turbo spin-echo (HASTE, Siemens Medical Solutions scanners) are frequently described in dynamic MRI of the pelvic floor and are performed at our institution. Alternatively, true fast imaging in steady-state precession may be performed. The patient should be given instructions as to the proper performance of straining before the examination. Specifically, she should be told to keep her sacrum on the table and strain using only the internal organs. The images are acquired in the sagittal plane and can be viewed in a cine loop to visualize the pelvic floor and the degree of prolapse of the pelvic organs.

For patients with a rectocele, these images should be repeated after the patient evacuates the rectal contents. The evacuation sequence can be obtained with the patient in the magnet and recorded if the magnet has been adequately prepared and the patient is able to cooperate with instructions. However, if the patient cannot evacuate in the magnet, evacuation in the commode followed by repeated imaging may be necessary. Residual contrast material will define a significant rectocele. In patients with pelvic organ prolapse, static images may be acquired in the coronal plane. These images show ballooning of the iliococcygeus muscle that often occurs with chronic constipation and perineal hernias.

After the dynamic examination is completed, small-field-of-view (20–24 cm) T2-weighted axial fast spin-echo (FSE, GE Healthcare scanners) or axial turbo spin-echo (TSE, Siemens Medical Solutions scanners) sequences are acquired to obtain high-resolution images of the muscles and fascia of the pelvic floor and the fascial condensations supporting the urethra. Although this set of images requires approximately 4 minutes to acquire, images of the lower pelvis are resistant to breathing motion artifacts. These high-resolution axial images of the pelvis are useful in showing the relationship between the pelvic side wall and the urethra and vagina. Fat saturation is generally not applied to these sequences because the hyperintense signal of fat in the pelvis provides good contrast to the hypointense signal of the adjacent muscles, fascia, and pubic bones. The entire examination is typically completed in 20 minutes. A suggested protocol for MRI of pelvic floor dysfunction is summarized in Table 1.

Interpretation of MRI Findings

Top Abstract Introduction Anatomy Imaging Imaging Technique Interpretation of MRI Findings Urinary Incontinence and... Middle Compartment Prolapse Posterior Compartment Prolapse Summary References

 
The level of the pelvic floor on dynamic MRI can be demarcated radiologically on the midsagittal image using the pubococcygeal line as described by Yang et al. [22] (Fig. 2A, 2B). This line extends from the most inferior portion of the pubic symphysis to the last horizontal sacrococcygeal joint. This line is easily drawn and highly reproducible on MRI in all patients. The levator plate should be parallel to the pubococcygeal line in normal individuals. Furthermore, two other reference lines, the H and M lines, are used, which may be a useful guide in identifying pelvic floor relaxation and prolapse [24]. The H line measures the distance from the inferior symphysis pubis to the posterior anorectal junction on the midsagittal image and is indicative of the anteroposterior width of the levator hiatus. The M line is drawn perpendicular from the pubococcygeal line to the most distal aspect of the H line and is indicative of the descent of the levator hiatus from the pubococcygeal line. In the study by Comiter et al. [24], the H line and M line in normal women measured approximately 5 and 2 cm, respectively.

View larger version (111K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2A —22-year-old woman with mild symptoms of pelvic floor weakness. Sagittal HASTE MR images of female pelvis show normal position of pelvic viscera at rest (A) and when straining (B). P, H, and M indicate normal pubococcygeal and H and M lines. Arrow in B indicates normal position of bladder neck when straining.

View larger version (109K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2B —22-year-old woman with mild symptoms of pelvic floor weakness. Sagittal HASTE MR images of female pelvis show normal position of pelvic viscera at rest (A) and when straining (B). P, H, and M indicate normal pubococcygeal and H and M lines. Arrow in B indicates normal position of bladder neck when straining.

The high-resolution T2-weighted axial images of the pelvic floor should be analyzed for signal intensity, symmetry, thickness, and fraying of the pelvic floor muscles. The vagina is suspended between the urethra and the rectum by the paracolpium and should maintain a normal butterfly configuration and be well centered in the pelvis in women with normal anatomy (Fig. 3). Although the periurethral ligaments may not be clearly shown without an endovaginal coil, wherever possible the symmetry and integrity of the periurethral ligaments should be analyzed, especially in women with symptoms of urinary incontinence.

View larger version (130K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3 —22-year-old woman with mild symptoms of pelvic floor weakness. Axial T2-weighted turbo spin-echo MR image of pelvis shows normal butterfly shape of vagina (V), normal configuration, thickness and signal intensity of puborectalis muscle (PR), normal rectum (R), normal urethra (U), and adjacent normal periurethral ligaments.

Top Abstract Introduction Anatomy Imaging Imaging Technique Interpretation of MRI Findings Urinary Incontinence and... Middle Compartment Prolapse Posterior Compartment Prolapse Summary References

Assessment and treatment of women with symptoms of urinary incontinence and pelvic floor weakness are multidisciplinary exercises involving urologists, urogynecologists, psychologists, physical therapists, and radiologists. Treatment begins with conservative measures such as pelvic floor exercise, use of a pessary, and lifestyle modifications. When these techniques are ineffective, surgery is required.

Support of the urethra arises from the pelvic muscles and fasciae. Condensations of the endopelvic fascia provide ligamentous support of the urethra. In a study of supporting ligaments of the female urethra by Macura et al. [25] using high-resolution MRI and an endourethral MR coil, three groups of ligaments supporting the female urethra were described: the periurethral ligaments arising from the puborectalis muscle and coursing ventral to the urethra, the paraurethral ligaments arising from the lateral wall of the urethra to the periurethral ligaments, and the pubourethral ligaments (Fig. 4). This network of ligaments and the anterior vaginal wall provide a hammocklike support to the urethra; together with the pelvic diaphragm, which elevates the urinary bladder and elongates the urethra, these support mechanisms play an important role in maintaining urinary continence in women [26]. Many studies have shown that disruption of this hammocklike support structure is closely related to the development of stress urinary incontinence in women [27–30].

View larger version (124K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4 —33-year-old woman with severe urinary incontinence. Sagittal HASTE MR image of pelvis at strain shows cystocele (arrow) and abnormal urethra hypermobility, in which urethra assumes horizontal orientation (arrowhead). Also note abnormal position of bladder neck below pubococcygeal line. Mild inferior descent of rectum at strain is within normal limits.

Yang et al. [22] reported that the normal vertical distance of the bladder neck at strain should be less than 1 cm from the pubococcygeal line. The distal two thirds of the urethra is inseparable from the anterior vaginal wall. In patients with stress urinary incontinence, the support from the anterior vaginal wall is diminished; increased intraabdominal pressure results in descent of the bladder neck below the pubococcygeal line and prolapse of the urinary bladder through the anterior vaginal wall, resulting in a cystocele. Because the bladder neck and proximal urethra are mobile, descent of the bladder neck during strain may result in clockwise rotational descent of the bladder neck and proximal urethra. When the proximal urethra rotates more than 30°, urethral hypermobility results and can cause kinking of the proximal urethra that may mask stress urinary incontinence [31]. In a study by Kim et al. [9], distortion of the periurethral and paraurethral ligaments was frequently noted in patients with stress urinary incontinence, suggesting that a defect of connection between the urethra and the puborectalis sling is one of the principal causes of urethral hypermobility.

The normal butterfly shape of the vagina may also be altered by weakening of the paravaginal ligaments. The vagina may have a flattened appearance because the vaginal wall will be displaced posteriorly as a result of loss of paravaginal attachments. The disruption to the paravaginal ligaments will weaken support to the urethra because the middle and distal thirds of the urethra are closely related to and supported by the anterior vaginal wall. The loss of the normal shape of the vagina is therefore a good indication of paravaginal tears in patients with urinary incontinence. This information will be relevant to the surgeon because repair of the cystocele alone will not be sufficient, and fascial repair may also be necessary [32, 33].

Middle Compartment Prolapse

Top Abstract Introduction Anatomy Imaging Imaging Technique Interpretation of MRI Findings Urinary Incontinence and... Middle Compartment Prolapse Posterior Compartment Prolapse Summary References

 
The middle compartment of the pelvic floor consists of the reproductive organs, the uterus, the cervix, and the vagina. Vaginal support in the pelvis has been described by DeLancey [28] as having three levels of support. The cephalic 2- to 3-cm portion of the vagina, described as level 1, is suspended from the pelvic side wall by the parametrium and paracolpium, which are condensations of the endopelvic fascia. Level 3 is described as the level that starts at the hymen ring and extends 2–3 cm cephalad to it, and level 2 is between levels 1 and 3. Level 2 of the vagina is attached to the arcus tendineus, although level 3 is directly fused anteriorly to the urethra, laterally to the levator ani muscles, and posteriorly to the perineal body, rather than being attached to or suspended from the pelvic walls. Note that the distal third of the vagina has a different embryologic origin from the proximal two thirds of the vagina.

View larger version (121K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5A —Axial T2-weighted turbo spin-echo MR images of pelvis in two patients with symptoms of pelvic floor dysfunction. 21-year-old woman with symptoms of defecatory dysfunction. Note complete tear of right puborectalis muscle (arrow) and loss of normal butterfly shape of vagina.

View larger version (130K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5B —Axial T2-weighted turbo spin-echo MR images of pelvis in two patients with symptoms of pelvic floor dysfunction. 36-year-old woman with symptoms of defecatory dysfunction. Note asymmetric appearance of puborectalis muscles. Right puborectalis muscle (arrow) shows slight ballooning, has convex morphology, and is torn anteriorly at insertion to pubis.

Although loss of the normal butterfly shape of the vagina is widely described as a sign of disruption of the paravaginal ligaments, loss of the normal shape of the vagina on MRI can also be seen in nulliparous asymptomatic women and in the absence of relevant clinical symptoms; therefore, the diagnosis of weakening of vaginal support should not be made based on vaginal shape alone [34].

The parametrium, consisting of the uterosacral and cardinal ligaments, suspends the uterus and cervix from the pelvic side walls. On midsagittal MR images, descent of the uterus in addition to descent of the cervix and vagina usually suggests disruption of the uterosacral or cardinal ligaments. The H and M lines may be elongated. On axial images, the transverse dimension of the levator hiatus may be widened, the levator muscles may be asymmetric and assume a convex morphology, and the vagina may also be flattened or lose the symmetric butterfly shape (Fig. 5A, 5B). The size of the urogenital hiatus in the levator muscles, a measurement that is determined clinically by physical examination, has been found to be larger in patients with pelvic organ prolapse [35]. A fibroid in the uterus may prevent descent of the uterus and cause underestimation of the true degree of pelvic floor dysfunction and supporting fascial damage. In severe cases, procidentia results and the entire uterus prolapses and lies outside the introitus.

View larger version (119K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 6 —36-year-old woman with symptoms of rectal prolapse. Sagittal HASTE MR image of pelvis at strain shows large rectocele (arrow) and abnormal caudal angulation of levator plate (arrowhead), indicating significant weakness of posterior compartment of pelvic floor.

Top Abstract Introduction Anatomy Imaging Imaging Technique Interpretation of MRI Findings Urinary Incontinence and... Middle Compartment Prolapse Posterior Compartment Prolapse Summary References

The levator plate, the midline raphe of the iliococcygeus muscle, is easily identified on the midsagittal image of the dynamic MR examination; it should remain parallel to the pubococcygeal line in normal individuals [36]. Caudal angulation of the levator plate on the midsagittal MR image by more than 10° with respect to the pubococcygeal line is a sign of pelvic floor weakness [33].

The most common cause of posterior vaginal bulge is anterior rectocele, caused by herniation of the anterior wall of the rectum into the posterior vaginal wall as a result of weakness in the rectovaginal fascia. On the midsagittal image of the dynamic MR examination, rectocele is identified by a rectal bulge of more than 3 cm, which is the distance measured between the anal canal and the tip of the rectocele [37] (Fig. 6). Because an anterior rectal bulge of up to 3 cm may also occur in women without defecatory dysfunction, the patient's clinical symptoms, such as a feeling of incomplete defecation, should be considered in determining the significance of this finding on MR examination [38]. Although physical examination is sufficient for diagnosis of a simple anterior rectocele, it is unreliable in assessing more complex posterior compartment prolapse such as an enterocele. In a study involving 300 women, enteroceles were revealed with dynamic cystoproctography in 111 subjects; 93 of these were missed on physical examination [39]. Moreover, it may be impossible to determine exactly which organ is causing the posterior vaginal bulge on physical examination. The superior soft-tissue contrast of MRI allows the posterior compartment to be seen in great detail, such as the hyperintense T2 signal of peritoneal fat in peritoneoceles, the hyperintense fluid-filled small-bowel loops in enteroceles, and the hyperintense gel-filled rectum or sigmoid colon in rectoceles or sigmoidoceles.

Prolapse of peritoneal contents is due to deficiency of the supporting ligaments and iliococcygeus muscle, resulting in widening of the rectovaginal space. In normal individuals, the rectovaginal space caudal to the upper third of the vagina is closely apposed [19]. Widening of this space will allow inferior herniation of the peritoneal fat, small bowel, sigmoid colon, and fluid into the pouch of Douglas. Prior hysterectomy may cause disruption of the rectovaginal fascia and increase the risk of enterocele formation [40]. A large enterocele may mask a coexisting cystocele or rectocele because of the tight space in the pelvic floor. Reduction of the enterocele may be required before assessment of the other compartments of the pelvic floor can be performed. Conversely, a persistently large rectocele or incomplete evacuation of the rectal contents in a large rectocele may also mask an enterocele or a cystocele [40]. Adequate evacuation of the rectal contents during the dynamic MR examination is required to completely assess the pelvic floor. With adequate evacuation of the rectal contents, intussusception of the rectum where the rectum invaginates distally toward the anal canal may occasionally be identified on dynamic supine MR images, although the study by Bertschinger et al. [16] found that all rectal intussusceptions identified on sitting MR defecography were missed on supine MR examinations.

Summary

Top Abstract Introduction Anatomy Imaging Imaging Technique Interpretation of MRI Findings Urinary Incontinence and... Middle Compartment Prolapse Posterior Compartment Prolapse Summary References

 
It has been long known that women with symptoms of pelvic floor dysfunction frequently have involvement of multiple compartments. MRI of the pelvic floor allows simultaneous assessment of all three compartments of the pelvic floor before surgery in patients with pelvic floor dysfunction and patients in whom conservative management is unsuccessful. In so doing, MRI may reduce the risk of surgical failure and the recurrence or persistence of the debilitating symptoms after surgery.

The use of ultrafast T2-weighted sagittal MRI described in this article allows noninvasive dynamic imaging of the pelvic floor, providing anatomic and functional information that will be useful to urogynecologists and surgeons. In addition, the use of high-resolution axial T2-weighted sequences of the pelvis allows identification of torn muscles and ligaments in patients with pelvic floor dysfunction who require surgery. The use of the pubococcygeal and H and M reference lines in the interpretation of the MR images is a simple method of identifying pelvic organ descent. For complete assessment of the severity of pelvic organ prolapse, MRI findings should be correlated with the severity of the patient's clinical symptoms.

References

Top Abstract Introduction Anatomy Imaging Imaging Technique Interpretation of MRI Findings Urinary Incontinence and... Middle Compartment Prolapse Posterior Compartment Prolapse Summary References

 

1. Wilson L, Brown JS, Shin GP, Luc KO, Subak LL. Annual direct cost of urinary incontinence. Obstet Gynecol2001; 98:398 –406[CrossRef][Medline]
2. Thom D. Variation in estimates of urinary incontinence prevalence in the community: effects of differences in definition, population characteristics, and study type. J Am Geriatr Soc1998; 46:473 –478[Medline]
3. Olsen Al, Smith VJ, Bergstrom JO, Colling JC, Clark AL. Epidemiology of surgically managed pelvic organ prolapse and urinary incontinence. Obstet Gynecol 1997;89 : 501–506[CrossRef][Medline]
4. Rowe JW, Beedine RW, Ford AB, et al. NIH consensus development panel: urinary incontinence in adults. JAMA1989; 261:2685 –2690[Abstract/Free Full Text]
5. Hendrix SL, Clark A, Nygaard I, Aragaki A, Barnabei V, McTiernan A. Pelvic organ prolapse in the Women's Health Initiative: gravity and gravidity. Am J Obstet Gynecol 2002;186 :1160 –1166[CrossRef][Medline]
6. Delancey JO, Kearney R, Chou Q, Speights S, Binno S. The appearance of levator ani muscle abnormalities in magnetic resonance images after vaginal delivery. Obstet Gynecol 2003;101 : 46–53[CrossRef][Medline]
7. Buchsbaum GM, Chin M, Glantz C, Guzick D. Prevalence of urinary incontinence and associated risk factors in a cohort of nuns. Obstet Gynecol 2002;100 : 226–229[CrossRef][Medline]
8. Clark MH, Scott M, Vogt V, Benson JT. Monitoring pudendal nerve function during labor. Obstet Gynecol2001; 97:637 –639[CrossRef][Medline]
9. Kim JK, Kim YJ, Choo MS, Cho KS. The urethra and its supporting structures in women with stress urinary incontinence: MR imaging using an endovaginal coil. AJR 2003;180 :1037 –1044[Abstract/Free Full Text]
10. Kelvin FM, Hale DS, Maglinte DD, Patten BJ, Benson JT. Female pelvic organ prolapse: diagnostic contribution of dynamic cystoproctography and comparison with physical examination. AJR1999; 173:31 –37[Abstract/Free Full Text]
11. Gonzalez-Argente FX, Jain A, Nogueras JJ, Davila GW, Weiss EG, Wexner SD. Prevalence and severity of urinary incontinence and pelvic genital prolapse in females with anal incontinence or rectal prolapse..Dis Colon Rectum 2001; 44:920 –926[Medline]
12. Ng CS, Rackley RR, Appell RA. Incidence of concomitant procedures for pelvic organ prolapse and reconstruction in women who undergo surgery for stress urinary incontinence. Urology2001; 57:911 –913[Medline]
13. Maglinte DD, Kelvin FM, Fitzgerald K, Hale DS, Benson JT. Association of compartment defects in pelvic floor dysfunction. AJR 1999; 172:439 –444[Abstract/Free Full Text]
14. Hetzer FH, Andreisek G, Tsagari C, Sahrbacher U, Weishaupt D. MR defecography in patients with fecal incontinence: imaging findings and their effect on surgical management. Radiology2006; 240:449 –457[Abstract/Free Full Text]
15. Martin DR, Salman K, Wilmot CC, Galloway NT. MR imaging evaluation of the pelvic floor for the assessment of vaginal prolapse and urinary incontinence. Magn Reson Imaging Clin N Am2006; 14:523 –535[Medline]
16. Bertschinger KM, Hetzer FH, Roos JE, Treiber K, Marincek B, Hilfiker PR. Dynamic MR imaging of the pelvic floor performed with patient sitting in an open-magnet unit versus with patient supine in a closed-magnet unit. Radiology 2002;223 : 501–508[Abstract/Free Full Text]
17. Fielding JR, Griffiths DJ, Versi E, Mulkern RV, Tee MLT, Jolesz FA. MR imaging of pelvic floor continence mechanisms in the supine and sitting positions. AJR 1998;171 :1607 –1610[Abstract/Free Full Text]
18. Grousse AE, Barbaric ZL, Safir MH, Madjar S, Marumoto AK, Raz S. Dynamic half-Fourier acquisition, single-shot turbo spin-echo magnetic resonance imaging for evaluating the female pelvis. J Urol 2000; 164:1606 –1613[CrossRef][Medline]
19. Lienermann A, Anthuber C, Baron A, Reiser M. Diagnosing enteroceles using dynamic magnetic resonance imaging. Dis Colon Rectum 2000; 43:205 –212[CrossRef][Medline]
20. Kelvin FM, Maglinte DD, Hale DS, Benson JT. Female pelvic organ prolapse: a comparison of triphasic dynamic MR imaging and triphasic fluoroscopic cystocolpoproctography. AJR2000; 174:81 –88[Abstract/Free Full Text]
21. Kruyt RH, Delemarre JBVM, Doornbos J, Vogel HJ. Normal anorectum: dynamic MR imaging anatomy. Radiology1991; 179:159 –163[Abstract/Free Full Text]
22. Yang A, Mostwin JL, Rosenheim NB, Zerhouni EA. Pelvic floor descent in women: dynamic evaluation with fast MR imaging and cinematic display. Radiology 1991;179 : 25–33[Abstract/Free Full Text]
23. Lienermann A, Anthuber C, Baron A, Kohz P, Reiser M. Dynamic MR colpocystography assessing pelvic floor descent. Eur Radiol 1997; 7:1309 –1317[CrossRef][Medline]
24. Comiter CV, Vasavada SP, Barbaric ZL, Gousse AE, Raz S. Grading pelvic floor prolapse and pelvic floor relaxation using dynamic magnetic resonance imaging. Urology 1999;54 : 454–457[CrossRef][Medline]
25. Macura KJ, Genadry RR, Bluemke DA. MR imaging of the female urethra and supporting ligaments in assessment of urinary incontinence: spectrum of abnormalities. RadioGraphics 2006;26 :1135 –1149[Abstract/Free Full Text]
26. Oelrich T. The striated urogenital sphincter muscle in the female. Anat Rec 1983;205 : 223–232[CrossRef][Medline]
27. DeLancey JO. Structural support of the urethra as it relates to stress urinary incontinence: the hammock hypothesis. Am J Obstet Gynecol 1994; 170:1713 –1723[Medline]
28. DeLancey JO. Correlative study of paraurethral anatomy. Obstet Gynecol 1986;68 : 91–97[Medline]
29. Cruikshank SH, Kovac SR. The functional anatomy of the urethra: role of the pubourethral ligaments. Am J Obstet Gynecol 1997; 176:1200 –1205[CrossRef][Medline]
30. Klutke C, Golomb J, Barbaric Z, Raz S. The anatomy of stress incontinence: magnetic resonance imaging of the female bladder neck and urethra. J Urol 1990;143 : 563–566[Medline]
31. Bergman A, McCarthy TA, Ballard CA, Yanai J. Role of the Q-tip test in evaluating stress urinary incontinence. J Reprod Med 1987; 32:273 –275[Medline]
32. Stoker J, Halligan S, Bartram CI. Pelvic floor imaging. Radiology 2001;218 : 621–641[Abstract/Free Full Text]
33. Fielding JR. MR imaging of pelvic floor relaxation. Radiol Clin N Am 2003;41 : 747–756[CrossRef][Medline]
34. Macura KJ. Magnetic resonance imaging of pelvic floor defects in women. Top Magn Reson Imaging 2006;17 : 417–426[Medline]
35. Delancey JO, Hurd WW. Size of the urogenital hiatus in the levator ani muscles in normal women and women with pelvic organ prolapse. Obstet Gynecol 1998;91 : 364–368[CrossRef][Medline]
36. Ozasa H, Mori T, Togashi K. Study of uterine prolapse by magnetic resonance imaging: topographical changes involving the levator ani muscle and the vagina. Gynecol Obstet Invest 1992;34 : 43–48[Medline]
37. Yshioka K, Matsui Y, Yamado O, et al. Physiologic and anatomic assessment of patients with rectocele. Dis Colon Rectum 1991; 34:704 –708[CrossRef][Medline]
38. Felt-Bersma RJ, Cuesta MA. Rectal prolapse, rectal intussusception, rectocele, and solitary rectal ulcer syndrome. Gastroenterol Clin North Am 2001; 30:199 –222[Medline]
39. Kelvin FM, Maglinte DDT, Hornback JA, Benson JT. Pelvic prolapse: assessment with evacuation proctography (defecography). Radiology 1992;184 : 547–551[Abstract/Free Full Text]
40. Mellgren A, Johansson C, Dolk A, et al. Enterocele demonstrated by defaecography is associated with other pelvic floor disorders. Int J Colorectal Dis 1994; 9:121 –124[Medline]
41. Cardozo L. Urogynecology. New York, NY: Churchill-Livingstone, 1997:325 –326

CiteULike

Complore

Connotea

Del.icio.us

Digg

Reddit

Technorati

This article has been cited by other articles:

				G. L. Bennett, E. M. Hecht, T. P. Tanpitukpongse, J. S. Babb, B. Taouli, S. Wong, N. Rosenblum, J. A. Kanofsky, and V. S. Lee MRI of the Urethra in Women With Lower Urinary Tract Symptoms: Spectrum of Findings at Static and Dynamic Imaging Am. J. Roentgenol., December 1, 2009; 193(6): 1708 - 1715. [Abstract] [Full Text] [PDF]

This Article Abstract Figures Only Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Law, Y. M. Articles by Fielding, J. R. Search for Related Content PubMed PubMed Citation Articles by Law, Y. M. Articles by Fielding, J. R. Social Bookmarking                      What's this? Hotlight (NEW!) What's Hotlight?