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MRI of Pelvic Floor Dysfunction: Self-Assessment Module

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 July 17, 2008; accepted after revision July 17, 2008.

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

Abstract

Top Abstract INTRODUCTION EDUCATIONAL OBJECTIVES REQUIRED READING RECOMMENDED READING INSTRUCTIONS References

 
Objective

The educational objectives of this continuing medical education activity are for the reader to exercise, self-assess, and improve skills in diagnostic radiology with regard to the interpretation of MRI of the female pelvis in the evaluation of pelvic floor dysfunction, and to improve familiarity with the clinical features of female pelvic floor dysfunction.

Conclusion

The articles in this activity review the anatomy and etiology of pelvic floor weakness in women and discuss the role of MRI in the assessment of female pelvic floor dysfunction.

Keywords: cystocele • MRI • pelvic floor dysfunction • rectocele

INTRODUCTION

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This self-assessment module on MRI of pelvic floor dysfunction has an educational component and a self-assessment component. The educational component consists of two required articles that the participant should read and three recommended articles that may provide additional information and perspective. The self-assessment component consists of 10 multiple-choice questions with solutions. All of these materials are available on the ARRS Website (www.arrs.org). To claim CME and SAM credit, each participant must enter his or her responses to the questions online.

EDUCATIONAL OBJECTIVES

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By completing this educational activity, the participant will:

1. Exercise, self-assess, and improve his or her understanding of the imaging features of pelvic floor dysfunction.
   
2. Exercise, self-assess, and improve his or her understanding of the clinical features of pelvic floor dysfunction.
   

REQUIRED READING

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1. Law YM, Fielding JR. MRI of pelvic floor dysfunction: review. AJR 2008; 191[suppl]:S45–S53
   
2. 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
   

RECOMMENDED READING

Top Abstract INTRODUCTION EDUCATIONAL OBJECTIVES REQUIRED READING RECOMMENDED READING INSTRUCTIONS References

 

1. 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. Radiology 2006; 240:449–457
   
2. 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 Am 2006; 14:523–535
   
3. Macura KJ. Magnetic resonance imaging of pelvic floor defects in women. Top Magn Reson Imaging 2006; 17:417–426
   

INSTRUCTIONS

Top Abstract INTRODUCTION EDUCATIONAL OBJECTIVES REQUIRED READING RECOMMENDED READING INSTRUCTIONS References

 

1. Complete the required reading.
   
2. Visit www.arrs.org and select Publications/Journals/SAM Articles from the left-hand menu bar.
   
3. Using your member login, order the online SAM as directed.
   
4. Follow the online instructions for entering your responses to the self-assessment questions and complete the test by answering the questions online.
   

QUESTION 1 Regarding the risk factors for pelvic floor dysfunction, which one of the following statements is FALSE? Age, sex, and vaginal parity are established risk factors for pelvic floor dysfunction. Nulliparous women are spared pelvic floor dysfunction. Vaginal delivery results in neuromuscular damage that can occur much earlier than the onset of pelvic floor dysfunction. With advanced age, hypoestrogenemia during menopause results in progression of symptoms of pelvic floor dysfunction. Not all women who undergo vaginal delivery suffer from pelvic floor dysfunction. QUESTION 2 Which of the following statements regarding urinary incontinence is FALSE? Stress urinary incontinence is involuntary and results from an increase in intraabdominal pressure. Stress urinary incontinence is related to urethral sphincter deficiency. Compared with stress and urge urinary incontinence, overflow urinary incontinence is less common in women. Overflow urinary incontinence never occurs in bladder outlet obstruction. Urge urinary incontinence results in leakage of a large volume of urine when the patient experiences a sudden urge to void. QUESTION 3 Which of the following statements regarding the endopelvic fascia and perineal body is TRUE? The endopelvic fascia lies deep in relation to the levator ani. The parametrium and paracolpium support the rectum and small bowel. The condensations of the endopelvic fascia are well visualized on conventional MRI without any need for an endovaginal coil. The perineal body separates the rectum from the vagina. The iliococcygeus muscle of the levator ani arises from the endopelvic fascia and attaches to the pelvic side wall. QUESTION 4 Which structure plays the most important role in apposing the orifices of the pelvic floor and elevating the bladder neck? The levator plate. The iliococcygeus muscle. The puborectalis muscle. The symphysis pubis. The rectovaginal fascia. QUESTION 5 Which one of the following statements regarding MRI of pelvic floor dysfunction in women is FALSE? Sitting MR defecography performed on a 0.5-T MR system is superior to conventional dynamic supine MRI for the depiction of clinically relevant bladder descents and rectoceles. Instilling a small volume of intraluminal ultrasonic gel that has a hyperintense T2 signal into the vagina and rectum allows improved visualization of the pelvic viscera. Fat saturation is conventionally not applied in dynamic supine MRI of the pelvic floor. The conventional sequences used in dynamic MRI of the pelvic floor are the rapid T2-weighted sequences such as single-shot fast spin echo or HASTE. The pelvic floor muscles and the levator plate are well visualized on conventional MRI. QUESTION 6 In interpreting the MRI findings of women with pelvic floor dysfunction, which one of the following statements is TRUE? Caudal angulation of the levator plate by 5° with respect to the pubococcygeal line is a significant sign of pelvic floor weakness. The pubococcygeal line extends from the superior pubic ramus to the last sacrococcygeal joint. The H and M reference lines are shortened in patients with significant pelvic floor dysfunction. The bladder neck at strain should be less than 3 cm from the pubococcygeal line in patients with normal anatomy. The H and M reference lines used in grading the extent of pelvic organ descent are indicative of the anteroposterior width of the levator hiatus and descent of the levator hiatus from the pubo coccygeal line, respectively. QUESTION 7 Regarding the vagina, which one of the following statements is TRUE? The distal two thirds of the vagina have a different embryologic origin from the proximal one third. The loss of the normal butterfly shape of the vagina is a significant sign in itself and is a strong indication of weakening of vaginal support. There is normally a gap in the rectovaginal fascia caudal to the upper third of the vagina. In patients who have had a hysterectomy, the normal vaginal apex routinely descends 3 cm below the pubococcygeal line at strain. The distal one third of the vagina is not suspended from the pelvic side wall by the paravaginal ligaments. QUESTION 8 In posterior compartment prolapse, which one of the following statements is TRUE? Intussusception of the rectum where the rectum invaginates distally toward the anal canal can be reliably identified when the examination is performed without evacuation of the rectal contents. The most common cause of posterior vaginal bulge is an enterocele. The rectovaginal fascia attaches to the perineal body and acts as an important support structure that prevents posterior compartment prolapse. A rectocele on dynamic supine MR examination is always associated with urinary incontinence. An anterior rectal bulge of 1 cm is abnormal and is diagnostic of a rectocele. QUESTION 9 In anterior compartment prolapse, which one of the following statements is TRUE? Urinary incontinence can be masked by urethral hypermobility due to kinking of the urethra. A video urodynamic study is not necessary. Urinary incontinence never occurs in the absence of a cystocele. Elevation of the bladder neck by the iliococcygeus muscle is important in maintaining urinary continence. Surgery is the first line of treatment for patients with urinary incontinence because they likely have complex multicompartment pelvic floor dysfunction. QUESTION 10 Which of the following statements regarding pelvic floor dysfunction is TRUE? Dynamic MRI of the pelvic floor provides detailed anatomic information that is useful in preoperative planning of patients with pelvic floor dysfunction. MRI of pelvic floor dysfunction is performed routinely for all patients with pelvic floor dysfunction, regardless of severity. Pelvic floor dysfunction usually involves only a single compartment; involvement of multiple compartments is rare. Any descent of the bladder neck at strain is always abnormal and is a sign of pelvic floor weakness. Procidentia is a form of posterior compartment prolapse.

 

Solution to Question 1
The consensus statement from the National Institutes of Health concluded that age, sex, and vaginal parity are established risk factors for pelvic floor dysfunction [1]. Option A is not the best response. Not all women who have undergone vaginal delivery develop pelvic floor dysfunction [2], and not all nulliparous women are free from pelvic floor dysfunction [3]. Electromyography studies have shown that vaginal delivery causes neuromuscular damage to the pelvic floor well before the onset of pelvic floor dysfunction [4]. Option C is not the best response. Hypoestro genemia and menopause can result in progressive weakening of the muscles, ligaments, and fascia that support the pelvic floor, resulting in progression of symptoms with advancing age. Option D is not the best response. Although epidemiologic evidence supports the relation between vaginal delivery and pelvic floor dysfunction, not all women who undergo vaginal delivery develop pelvic floor dysfunction, and not all nulliparous women are free from pelvic floor dysfunction. Option E is not the best response. As explained above [1], nulliparous women are therefore not spared from pelvic floor dysfunction. Option B, which is false, is the best response.

Solution to Question 2
Stress urinary incontinence is the involuntary loss of urine due to an increase in intraabdominal pressure such as coughing and sneezing; it is related to urethral sphincter deficiency. Options A and B are not the best responses. Urge incontinence and overflow urinary incontinence are related to bladder abnormalities. Urge urinary incontinence is due to detrusor instability or damage to the nervous system supplying the urinary bladder such as in multiple sclerosis, stroke, or pelvic injury; it results in leakage of a large amount of urine when the patient experiences a sudden urge to urinate. Option E is not the best response. In overflow urinary incontinence, leakage of a small amount of urine occurs when the urinary bladder is overdistended due to weakness of the bladder muscles in a neurogenic bladder or in chronic bladder outlet obstruction. Overflow incontinence is less common in women than in men. Option C is not the best response. Overflow incontinence occurs in chronic bladder outlet obstruction. Option D, which is false, is the best response.

Solution to Question 3
The endopelvic fascia is the most superior layer of the pelvic floor and covers the levator ani and the pelvic viscera in a continuous sheet. Option A is not the best response. The endopelvic fascia attaches the cervix and vagina to the pelvic side wall via the elastic condensations known as the parametrium and the paracolpium, respectively. These fascial condensations are not well visualized on conventional MRI; their defects may be inferred indirectly through secondary findings. Option B is not the best response. These ligaments may be better visualized with an endovaginal coil, which, if placed near the target organ, provides more detailed visualization of fine structures. Option C is not the best response. The iliococcygeus muscle has a horizontal orientation, arises from the external anal sphincter, and fans out laterally, attaching to the arcus tendineus. The iliococcygeus muscle does not arise from the endopelvic fascia. Option E is not the best response. The perineal body lies inferior to the levator ani muscles and separates the vagina and rectum. Option D, which is the only true answer, is the best response.

Solution to Question 4
The puborectalis muscle 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. Option C is the best response. The horizontally oriented iliococcygeus muscle, which arises from the external anal sphincter and fans out laterally, attaches to the arcus tendineus to act as an important physical barrier, preventing prolapse of the posterior compartment, which includes the rectum and the peritoneal contents. Option B is not the best response. The rectovaginal fascia is part of the endopelvic fascia that forms a supportive layer between the rectum and the vagina, preventing posterior compartment prolapse. Option E is not the best response. The symphysis pubis is a bony structure where the levator ani muscles attach anteriorly. Option D is not the best response. The levator plate is a firm raphe anterior to the coccyx from condensation of the iliococcygeus muscle. Option A is not the best response.

Solution to Question 5
The superior soft-tissue contrast of MRI allows direct visualization of the pelvic floor musculature and levator plate. Option E is not the best response. Rapid T2-weighted sequences such as single-shot fast spin echo or HASTE are the typical sequences described for dynamic MRI of the pelvic floor. Option D is not the best response. Fat saturation is generally not applied to MR sequences of the pelvic floor because the hyperintense signal of fat in the pelvis provides good contrast against the hypointense signal of the adjacent muscles, fascia, and pubic bones. Option C is not the best response. A small volume of intraluminal ultrasonic gel that has a hyperintense T2 signal may be instilled into the vagina and rectum to improve pelvic viscera visualization. Option B is not the best response. The presence of endoluminal gel in the rectum may improve straining efforts and increase the conspicuity of pelvic organ prolapse and visceral descent. Although MRI defecography performed in a 0.5-T open MR system with the patient in a sitting position more closely resembles the physiologic state, studies have shown that it is not superior to dynamic supine MRI for depiction of clinically relevant bladder descents and rectoceles [5, 6]. Option A, which is not true, is the best response.

Solution to Question 6
The level of the pelvic floor in dynamic pelvic floor MRI is demarcated radiologically on the midsagittal image by the pubococcygeal line, which extends from the most inferior portion of the pubic symphysis to the last sacrococcygeal joint [7]. Option B is not the best response. The H and M reference lines are used in pelvic floor imaging to identify pelvic organ descent [8]. The H and M lines are lengthened in patients with significant pelvic floor dysfunction. Option C is not the best response. 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. The presence of significant pelvic floor prolapse will result in sloping of the levator plate and increasing length of the H and M lines. The levator plate should remain parallel to the pubococcygeal line in normal subjects [9]. Option E is the best response. 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 [10]. Option A is not the best response. The normal vertical distance of the bladder neck at strain should be less than 1 cm from the pubococcygeal line [7]. Option D is not the best response.

Solution to Question 7
The distal one third of the vagina has a different embryologic origin from the proximal two thirds. Option A is not the best response. It is directly attached to its surrounding structures; anteriorly to the urethra, posteriorly to the perineal body, and laterally with the levator ani, and is not suspended from the pelvic side wall by the paravaginal ligaments. Option E is the best response. Although loss of the normal butterfly shape of the vagina on MRI is a sign of weakness of the paravaginal ligaments, it can also be seen in nulliparous asymptomatic women and in the absence of relevant clinical symptoms. The diagnosis of weakening of the vaginal support should not be made on the basis of vaginal shape alone [11]. Option B is not the best response. In patients with normal anatomy, the rectovaginal fascia caudal to the upper third of the vagina is closely apposed [12]. Option C is not the best response. Posterior compartment prolapse is due to deficiency of the supporting ligaments and muscles of the pouch of Douglas, resulting in widening of the rectovaginal space. When the patient has had a prior hysterectomy, support to the vaginal apex is provided by the paracolpium, and the vaginal apex should remain at least 1 cm above the pubococcygeal line at strain. Option D is not the best response.

Solution to Question 8
On dynamic MRI of the pelvic floor, a rectocele is identified by an anterior rectal bulge of more than 3 cm, which is the distance measured between the anal canal and the tip of the rectocele [13]. Option E is not the best response. An anterior rectal bulge of up to 3 cm may also occur in asymptomatic women without defecatory dysfunction and may not represent pelvic floor dysfunction [14]. Rectocele may be associated with defecatory dysfunction and is not always associated with urinary incontinence. Option D is not the best response. The most common cause of posterior vaginal bulge is an anterior rectocele caused by herniation of the anterior wall of the rectum into the posterior vaginal wall due to weakness in the rectovaginal fascia. Option B is not the best response. The rectovaginal fascia is the condensation of the endopelvic fascia that attaches to the perineal body, acting as a support diaphragm and preventing posterior prolapse. Option C is the best response. Intussusception of the rectum where it invaginates distally toward the anal canal may not be reliably identified on dynamic supine MRI. The study by Bertschinger et al. [5] found that all rectal intussusceptions identified on sitting MR defecography were missed on supine MR examinations [5]. Intussusception of the rectum may occasionally be identified on dynamic supine examinations when the rectal contents have been adequately evacuated. Option A is not the best response.

Solution to Question 9
Urethral hypermobility is due to rotational descent rather than vertical descent of the mobile bladder neck and proximal urethra. With a maximum Valsalva maneuver, descent of the mobile 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, which may mask stress urinary incontinence because it prevents leakage of urine from being detected clinically [15]. Option A is the best response. Most patients with mild symptoms of urinary continence benefit from a thorough physical examination and urodynamic study, which are important in assessing patients with urinary incontinence. Option B is not the best response. Urinary incontinence can occur without cystocele formation. Option C is not the best response. The puborectalis component of the levator ani and not the iliococcygeus muscle plays an important role in elevating the bladder neck and compressing it against the pubic symphysis, helping to maintain urinary continence. Option D is not the best response. Surgery is indicated only when conservative measures such as pelvic floor exercise, use of a pessary, and lifestyle modifications are ineffective in patients with urinary incontinence. Option E is not the best response.

Solution to Question 10
Several studies have shown that patients with urinary incontinence have coexisting pelvic organ prolapse in the other two compartments, requiring surgical repair [16–18]. It is therefore not uncommon that patients with pelvic floor dysfunction have involvement of multiple compartments. Option C is not the best response. MRI of pelvic floor dysfunction is not indicated in patients with mild symptoms of pelvic floor dysfunction such as a small cystocele or mild urinary incontinence. Option B is not the best response. However, MRI is an invaluable tool in preoperative planning in patients with severe pelvic floor dysfunction who require surgical repair. Option A is the best response. Mild descent of the bladder neck of less than 1 cm is seen in normal patients and is not a sign of pelvic floor dysfunction [7]. Option D is not the best response. Procidentia refers to prolapse of the uterus beyond the introitus and is a severe form of middle compartment prolapse. Option E is not the best response.

References

Top Abstract INTRODUCTION EDUCATIONAL OBJECTIVES REQUIRED READING RECOMMENDED READING INSTRUCTIONS References

 

1. Rowe JW, Beedine RW, Ford AB, et al. NIH consensus development panel: urinary incontinence in adults. JAMA1989; 261:2685 –2690[Abstract/Free Full Text]
2. 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]
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6. 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]
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11. Macura KJ. Magnetic resonance imaging of pelvic floor defects in women. Top Magn Reson Imaging 2006;17 : 417–426[Medline]
12. Lienermann A, Anthuber C, Baron A, Reiser M. Diagnosing enteroceles using dynamic magnetic resonance imaging. Dis Colon Rectum 2000; 43:205 –212[CrossRef][Medline]
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14. Felt-Bersma RJ, Cuesta MA. Rectal prolapse, rectal intussusception, rectocele, and solitary rectal ulcer syndrome. Gastroenterol Clin North Am 2001; 30:199 –222[Medline]
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16. 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]
17. 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]
18. 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]

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This Article Abstract Full Text (PDF) CME/SAM 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 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?