REVIEW ARTICLE
Magnetic Resonance Imaging of Pelvic Floor Disorders Gaurav Khatri, MD Abstract: Physical examination alone is often inadequate for evaluation of pelvic floor dysfunction. Magnetic resonance imaging (MRI) is a robust modality that can provide high-quality anatomic and functional evaluation of the pelvic floor. Although lack of standardized technique and radiologist inexperience may be relative deterrents in universal acceptance of pelvic floor MRI, the role of MRI is increasing as it is technically feasible on most magnets and offers some advantages over the traditional fluoroscopic defecography. This review focuses on the technical and interpretational aspects of anatomic and functional pelvic floor MRI. Key Words: MR defecography, dynamic MRI, pelvic organ prolapse, pelvic floor MRI, pelvic floor mesh (Top Magn Reson Imaging 2014;23: 259–273)
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elvic floor disorders are a complex set of conditions including pelvic organ prolapse, chronic pelvic pain, defecatory dysfunction, and urinary and fecal incontinence. An estimated nearly 1 in 4 women in the United States report symptoms of at least 1 pelvic floor disorder,1 and 75% of affected women report moderate to severe negative effect on their quality of life.2 The lifetime risk of undergoing a single surgical procedure for prolapse or incontinence by the age of 80 years is 11.1%3 with more than 200,000 annual surgical procedures in the United States.4,5 This likely represents but a fraction of women who suffer from pelvic floor disorders as many are managed nonsurgically or never actually present for clinical evaluation. Furthermore, the reoperation rate for recurrent prolapse is as high as 29%, implying a high rate of surgical failure.3 Direct surgical costs for pelvic floor dysfunction in the United States are reported to be more than $1 billion annually.4,6 The development of pelvic floor disorders is a multifactorial process, given the complex anatomy and function of the involved structures. Risk factors include advanced age, pregnancy and childbirth, hysterectomy, connective tissue abnormalities, injury to or denervation of pelvic floor musculature, obesity, smoking, and other conditions associated with chronically increased intra-abdominal pressure. In most cases, multiple compartments (anterior, middle, and posterior) of the pelvic floor are involved.7–11 Inadequacy of physical examination as the sole evaluation of the pelvic floor12,13 may be a contributing factor to the high surgical failure rate. Radiological evaluation of the pelvic floor has traditionally been performed with conventional fluoroscopic studies. A standing voiding cystourethrogram (VCUG) is a reproducible test to evaluate bladder and urethral mobility14; however, it does not provide information regarding the middle and posterior compartments. Dynamic cystocolpoproctography (DCP) has been routinely used for a more global functional assessment of pelvic floor dysfunction for a number of years15; however, it involves exposure to radiation and does
From the Department of Radiology, University of Texas Southwestern Medical Center, Dallas, TX. Reprints: Gaurav Khatri, MD, 5323 Harry Hines Blvd, Dallas, TX 75390 (e‐mail: [email protected]). The author declares no conflict of interest. Supplemental digital contents are available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s Web site (www.topicsinmri.com). Copyright ©2014 by Lippincott Williams & Wilkins
not allow for direct visualization of pelvic anatomy or structures. Magnetic resonance defecography (MRD) has evolved over the years as a potential alternative to DCP. Despite variations in MRD technique and wide range of “normal” findings in asymptomatic individuals,16,17 given its superior contrast resolution and multiplanar capabilities that enable direct visualization of pelvic floor anatomy and defects without exposure to radiation,18 MRD has developed as an important tool. Furthermore, MRD allows for global evaluation of the entire pelvis to depict prolapse in multiple compartments. In 1 study of patients with fecal incontinence, MRD influenced choice of surgical treatment in 67% of patients.9 Although some degree of prolapse has been reported on magnetic resonance imaging (MRI) in asymptomatic individuals, the degree of prolapse is generally greater in symptomatic patients.8 Furthermore, fluoroscopic defecography, which has traditionally been used for functional evaluation of the pelvic floor, also suffers from similar variability of findings in asymptomatic subjects.19,20 High costs, limited radiologist experience, and/or expertise in interpretation, as well as questions about reproducibility of pelvic measurements on dynamic MRI,21 are additional deterrents to universal acceptance of MRI for evaluation of the pelvic floor. This review focuses on the utility of MRI for anatomic as well as functional evaluation of the pelvic floor in order to address some of these limitations.
PELVIC FLOOR ANATOMY A brief review of the female pelvic floor anatomy is helpful to understand the complex nature of the problem because majority of functional pelvic floor disorders occur in women. The pelvic floor can be divided into 3 compartments. The anterior compartment contains the urinary bladder and urethra; the middle compartment refers to the uterus, cervix, and vagina; and the posterior compartment comprises the rectum and anal canal. Abnormalities in 1 compartment are frequently associated with dysfunction of other compartments.7,8 The compartments of the pelvic floor are supported by complex interplay of muscular, fascial, and ligamentous attachments to the pelvic skeleton. Fascial and ligamentous attachments of the pelvic floor comprise the passive support system, whereas the muscles of the pelvic floor are involved in active support. The 3 layers of the pelvic floor support structures include the endopelvic fascia most superiorly, the pelvic diaphragm in the middle, and the urogenital diaphragm most inferiorly.22–24 The endopelvic fascia is a layer of connective tissue that lines the pelvic floor, extending in a sheet-like fashion from the bony pelvis to cover the levator ani muscles and pelvic viscera. It is difficult to perceive on imaging. Various portions of the fascia are labeled according to their locations including the pubocervical fascia (between the bladder and vagina/cervix), rectovaginal fascia (between the vagina and rectum), parametrium (extending from the cervix to the pelvic sidewall), and paracolpium (extending from the vagina to the pelvic sidewall). Superiorly, prominent folds of the fascia form the cardinal and uterosacral ligaments. Lateral condensations of the fascia coalesce to form the arcus tendineus, which acts as a lateral support structure for the pelvic organs. The levator ani muscles as well as the pubocervical and rectovaginal fasciae insert upon the arcus tendineus laterally. Direct visualization of arcus tendineus is difficult because of its small size; its location can be inferred from the angle formed between the levator
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ani muscles and surface of the internal oblique muscles.23–25 The endopelvic fascia provides 3 levels of support of the pelvic floor based on its location: level I, the upper third of the vagina; level II, the middle third of the vagina; level III, lower third of the vagina.26 The pelvic diaphragm is well seen on imaging and consists of the levator ani muscles and the coccygeus (also known as ischiococcygeus) muscle. The puborectalis, pubococcygeus, and ileococcygeus muscles comprise the levator ani. This group of hourglass-shaped muscles forms the floor of the pelvis (Fig. 1A). They attach laterally to the arcus tendineus and come together centrally and posteriorly into a condensation of tissue called the levator plate, which inserts onto the sacrococcygeal joints. The puborectalis muscle, the most caudal of the levator ani muscles, is a sling-like or “U”-shaped muscle that arises anteriorly from the pubic symphysis and wraps around the anorectum (Fig. 1B). The impression of the puborectalis demarcates the anorectal junction (Fig. 1C). The pubococcygeus arises predominantly from the superior rami of the pubic symphysis anteriorly and inserts upon the levator plate posteriorly. It also has attachments upon the vagina, rectum, and perineal body, and its fibers overlap in a slinglike fashion with the puborectalis muscle. The pubococcygeus and puborectalis muscle are sometimes collectively referred to as the pubovisceralis muscle. The ileococcygeus is a thinner flat muscle more cranially that arises from the arcus tendineus laterally and inserts upon the levator plate posteriorly. The coccygeus muscle is a smaller component of the pelvic diaphragm that extends on either side from the ischial spine to the midline coccyx. It sits posterior to the ileococcygeus and covers the sacrospinous ligament.27 The pelvic diaphragm muscles provide constant passive tone to the pelvic floor, but also work in unison to actively tighten or relax the pelvic floor. The urogenital or levator hiatus is a “U-shaped” opening in the pelvic floor lined by the levator muscles (Fig. 1B). The urethra, vagina, and rectum pass through the hiatus, and widening of the hiatus results in pelvic organ prolapse. The average width of the levator hiatus in asymptomatic females is approximately 4 cm.28 The final and most caudal layer of the pelvic floor support structures is the urogenital diaphragm, also called the perineal membrane (Fig. 1A). This membrane is formed from primarily the deep transverse peroneus muscle as well as condensation of
connective tissue that extends horizontally from the ischium on either side to the perineal body in the midline with attachment anteriorly to the pubic symphysis, thus yielding a triangular shape. The perineal body is a connective tissue support structure located in the perineum between the anal verge and vaginal introitus. It is also called the central tendon of the perineum and is a site of attachment for multiple pelvic floor structures.23,24
MRI TECHNIQUE Because of the complex multicompartmental nature of pelvic floor disease, adequate evaluation requires both superior anatomic and functional imaging. Magnetic resonance imaging of the pelvic floor allows for dynamic evaluation of all compartments of the pelvic floor in a relatively noninvasive manner and without exposure to radiation. It provides multiplanar imaging, which can be of great utility when assessing the complex pelvic floor anatomy, particularly in postsurgical cases. Images with high spatial and soft tissue contrast resolution allow for direct visualization of the pelvic floor support structures and/or anatomic defects that may guide or alter management decisions,27 whereas the high temporal resolution allows for dynamic evaluation during straining and defecation. In cases of prior surgical intervention, MRI of the pelvic floor may help identify and evaluate previously placed mesh material and associated complications.29 An added benefit of MRI is detection of incidental or associated abnormalities in the pelvis, which may contribute to pelvic floor dysfunction (Fig. 2). Dynamic pelvic floor can be performed in an open magnet with the patient sitting upright, or in a conventional closed MRI unit with the patient supine. The sitting position may theoretically be more physiologic for studying the pelvic floor; however, the relative inaccessibility of open MRI units makes upright imaging less feasible and less reproducible across institutions. Gufler et al30 showed no significant difference in anterior and middle compartment prolapse between supine and upright colpocystoproctography and supine dynamic MRI in a small series of patients; however, the study was performed with strain rather than defecation. Another study comparing supine MRI during straining to sitting magnetic resonance (MR) with defecation found decreased sensitivity of the supine examination for rectal intussusception and bladder descent31;
FIGURE 1. A 46-year-old female with chronic pelvic pain. Coronal T2-weighted TSE image through the rectum (A) demonstrates the symmetric hourglass shape of the levator ani muscles at rest (dashed arrows) with upward convexity. The urogenital diaphragm or perineal membrane (solid arrows) is seen extending horizontally from the midline to the ischium on either side. Axial T2-weighted TSE image (B) at the level of the pubic symphysis demonstrates relatively symmetric “U-shaped” appearance of the puborectalis sling (arrows) outlining the urogenital or levator hiatus. The urethra (u), vagina (v), and rectum (r) are seen from anterior to posterior within the hiatus. Note the normal attachment of the puborectalis anteriorly upon the pubic bone (dashed arrows). Sagittal T2-weighted TSE image (C) to the left of midline shows the horizontally oriented puborectalis muscle, which can be used as a landmark to delineate the anorectal junction. A Bartholin’s gland cyst is incidentally seen (asterisk).
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MRI of Pelvic Floor Disorders
FIGURE 2. A 43-year-old female with history of prior pelvic mass resection presenting with defecatory dysfunction. Coronal T2-weighted TSE image (A) demonstrates intermediate signal intensity tissue (arrows) in the left ischioanal fossa causing a defect in the levator muscles. The gel-filled rectum is seen herniating laterally through the defect (asterisk). Sagittal T2-weighted TSE image slightly to the left of midline (B) shows the large confluent pelvic mass, a pathologically confirmed recurrent aggressive angiomyxoma (arrows) extending below the level of the urethra, as well as posteriorly in the ischiorectal fossa. The rectum (asterisk) demonstrates downward herniation through the pelvic floor defect at rest. On axial T2-weighted TSE image (C), the mass (arrows) is seen to obliterate the left levator muscles, producing a lateral defect for herniation of the rectum (asterisk) even at rest. This lateral rectocele increased in size during attempts at evacuation (not shown), resulting in the defecatory dysfunction.
however, lack of a defecation phase during supine MRI in that study confounds these findings. The defecation phase is imperative to adequate dynamic evaluation of the pelvic floor on MRI during upright32 and supine imaging.33 Kelvin et al34 did demonstrate that supine MR with defecation underestimates the extent of cystoceles and enteroceles relative to sitting DCP; however, to our knowledge, adequate comparisons of MR with defecation in supine position to MR with defecation in sitting position are lacking in the scientific literature. In our experience, supine MR defecography actually shows higher degrees of anterior compartment prolapse compared with upright VCUG.35 Furthermore, closed magnet systems used for supine MRD are of higher field strength and thus allow more detailed anatomic evaluation of the pelvic floor. Open magnets used for upright MRI suffer from lower signal-to-noise and relatively poor soft tissue resolution.36 We perform MRD in the supine position in a closed magnet at our institution. Given the unique nature of the examination, it is imperative to explain the procedure to the patient prior to arrival to avoid undue anxiety and embarrassment during the examination. We also suggest that the patient perform fleets enema prior to arrival to the department in order to clear the rectum, although this is not mandatory. Overdistention of the bladder can obscure prolapse in other compartments because of mass effect34,37; however, an empty bladder may limit evaluation of anterior compartment prolapse. Hence, the patient is asked to urinate upon arrival to the department and then drink 16 oz of water in an effort to attain some bladder distention in a noninvasive manner (ie, without placement of Foley catheter to drain or distend the bladder). The technologist reviews the procedure in detail; explains the Kegel (squeeze), Valsalva (strain), and defecation maneuvers to the patient; and addresses any concerns that patient may have regarding defection on the table prior to placing them in the magnet. The MRI table is covered with disposable absorbent pads. The patient is placed in lateral decubitus position within an inflatable MR-safe barium enema ring, and ultrasound gel (off-label use) is instilled in the rectum via a long catheter-tip syringe. The patient is then placed in supine position within the enema ring. The benefit of rectal contrast for MR defecography has been established previously38; however, the exact composition and volume of contrast media to be instilled in the rectum have been debated with different authors, ©2014 Lippincott Williams & Wilkins
suggesting a variety of substances including some thickened with potato starch to mimic the consistency of stool.39–41 We have encountered false negatives for prolapse (enteroceles) on MRI because of rectal (over)distention to 180 mL. Thus, based on a study at our institution, which showed a lower volume of 120 mL of gel to be as effective as 180 mL for inducing successful defecation,42 we routinely use 120 mL of intrarectal gel for our protocol. Once the patient has been prepared, T2-weighted turbo spin echo (TSE) sequences in axial, coronal, and sagittal planes as well as a T1-weighted sequence in the axial plane are acquired at rest. Functional imaging involves acquiring cine-type TrueFISP (true fast imaging with steady-state precession) images during dynamic maneuvers. TrueFISP acquisition demonstrates greater degree of prolapse in all 3 compartments than the HASTE (half-Fourier acquisition single-shot TSE) acquisition43 and is preferred for the cine imaging. The initial cine images are obtained through a single midline sagittal plane (which includes the pubic symphysis, urethra, vagina, anal canal, levator plate, and coccyx) during Kegel maneuver and then during defecation. The sagittal midline cine acquisition is repeated with defection if the patient is unable to evacuate on the initial attempt. We then obtain additional cine acquisitions in the coronal oblique plane (single slice angled through anal canal) as well as axial oblique plane along a line connecting the bottom of pubic symphysis and tip of the coccyx during additional defecation or maximal strain (if rectum is already empty) in an effort to visualize lateral defects that may not be readily visible on midline sagittal images. A final sagittal midline cine sequence (“postdefecation Valsalva”) is performed during maximal strain. Finally, we perform an additional axial high-resolution T2-weighted TSE for evaluation of the pelvic floor anatomy as muscle or anatomic defects may be more apparent immediately after strain or after defecation. Our institutional MRD protocol is detailed in Table 1.
MRI INTERPRETATION In our practice, we utilize a data collection sheet (Appendix 1, http://links.lww.com/TMRI/A8) to facilitate systematic interpretation and minimize variation between readers. We report findings using a dictation template (Appendix 2, http://links.lww.com/TMRI/A9) to ensure organization and consistency in reporting and grading of key findings in a manner agreed upon with our referring www.topicsinmri.com
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TABLE 1. Institutional MR Defecography Protocol Sequence
Imaging Plane
Maneuver
T2 TSE Axial Rest T2 TSE Sagittal Rest T2 TSE Coronal Rest T1 SE Axial Rest Cine TrueFISP Sagittal Kegel Cine TrueFISP Sagittal Defecation Cine TrueFISP Axial oblique Defecation Cine TrueFISP Coronal oblique Defecation Cine TrueFISP Sagittal Postdefecation Valsalva T2 TSE Axial Rest
Field of Slice Thickness, Repetition Time to Flip Angle, View, cm mm time, ms Echo, ms Degrees 26 26 26 26 34 34 33 33 34 26
physicians. These tools maximize efficiency and completeness in both anatomic and functional interpretation of pelvic floor MRI.
ANATOMIC EVALUATION Interpretation of the pelvic floor MRI should begin with an assessment of the anatomic structures as morphologic changes to these structures have been correlated with functional abnormalities of the pelvic floor.44,45 Although there is variability in the appearance of the pelvic support structures even in asymptomatic nulliparous women,46 significant differences in levator muscle volume, shape, and integrity have been shown between asymptomatic individuals and those with incontinence and pelvic prolapse.47 The levator muscles should be assessed for areas of asymmetric thickening or atrophy (Fig. 3), focal defects, scarring, ballooning (Fig. 4), or focal eventration on different planes of imaging.48 Identification of these anatomic abnormalities may predict the pattern of prolapse on the functional images. Care must be taken when evaluating the puborectalis muscle as it is often thinner on the right even in asymptomatic women when viewed in the axial plane, with thickness at the level of the proximal-middle urethra ranging from 2 to 5 mm on the right and 4 to 7 mm on the left.28,49 Anatomic defects of the puborectalis muscle are seen as lateral deviations anteriorly at the attachment site to the pubic bone50; can be unilateral or bilateral (resulting in a “batwing” appearance) (Fig. 5); may be secondary to trauma during vaginal delivery, episiotomy, or other vaginal surgery; and may predict subsequent pelvic floor
5 5 5 5 8 8 8 8 8 5
3920 4070 5120 625 734.4 734.4 742.6 946.4 734.4 3920
91 91 91 10 1.8 1.8 1.8 1.8 1.8 91
150 150 150 180 80 80 80 80 80 150
Matrix 320 256 320 256 320 256 256 192 256 256 256 256 256 256 256 256 256 256 320 256
dysfunction.51–54 Grading scales for these defects have been proposed.55,56 The anal sphincter complex must also be evaluated. The internal anal sphincter is seen as a thick circular muscle layer with variable hypointense or intermediate signal intensity on axial T2weighted images, whereas the external anal sphincter is seen as a thinner circumferential band of hypointense signal intensity (Fig. 6). It is important to note the integrity of the levator plate and its level of insertion upon the sacrum/coccyx (Fig. 7). The insertion of the levator plate may vary between individuals, and often the insertion may span multiple coccygeal segments with a dominant inserting band usually identifiable in most cases. There is also a certain mobility of the coccyx that occurs during defecation57,58 (Figs. 7B, C). Using the coccygeal tip as the posterior point of reference for the pubococcygeal line (PCL) has vulnerability to naturally occurring positional changes of the coccyx during the study. Therefore, we advocate using the last nonmobile coccygeal or sacrococcygeal joint. We have found that this often correlates with the dominant insertion of the levator plate. We document these anatomic landmarks in our report (Appendix 2, http://links.lww.com/TMRI/A9) in order to maintain reproducibility in interpretation. Morphologic assessment of the urethra and vagina is also important as abnormalities may suggest location of pelvic floor defects. A level I fascia defect, which results from detachment of the upper vagina from the uterosacral ligament, results in sagging of the vagina bilaterally (“chevron sign”).59,60 Deficiency in level II endopelvic fascial support of the middle third of the vagina combined with defects in the puborectalis muscle may result in
FIGURE 3. A 75-year-old female with remote history of multicompartment pelvic floor repair with recurrent prolapse. Axial T2-weighted TSE image at level of puborectalis muscle (A) shows asymmetry and absence of muscles on right (dashed arrow) due to complete tear. Left puborectalis muscle thickness is preserved (arrow). Coronal T2-weighted TSE image (B) shows asymmetric bulging of rectum on the right with absence/atrophy of the right puborectalis (dashed arrow). Left puborectalis is seen on end (arrow).
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FIGURE 4. A 70-year-old female with history of constipation. Axial T2-weighted TSE image at the level of the pubic symphysis demonstrates ballooning of puborectalis bilaterally (arrows).
disruption of the expected “H” or hammock shape of the vagina on axial images in patients with prolapse49 (Fig. 5); however, the vagina may have variable shape on imaging even in asymptomatic females.28 A lateral level II defect (paravaginal defect) on either side may result in posterior drooping of the posterior bladder wall on the affected side (“saddlebag sign”)59,60 (Fig. 8). Level III endopelvic fascia defects may involve disruption of the urethral suspension ligaments and resultant widening of the retropubic space (“mustache sign”).59,60 Although the normal circular target appearance of the urethra may become less distinct in postmenopausal females, flattening or funneling of the urethra (Fig. 9) and disruption of surrounding support structures can be seen in the setting of urethral incontinence.59,61
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FIGURE 6. A 62-year-old female with incontinence and prolapse symptoms. Axial T2-weighted TSE image just above the anal verge demonstrates thick circular internal anal sphincter (arrows). The thinner external anal sphincter muscle is seen extending more posteriorly (dashed arrows).
Patients with pelvic floor dysfunction often present after previous attempts at native tissue repair and/or synthetic pelvic mesh and tape placements. Identification of postsurgical changes and potential mesh and tape remnants is an important part of the anatomic evaluation. These postsurgical changes and mesh cannot be directly visualized on DCP. Differentiation of mesh from granulation or postsurgical fibrosis can often also be difficult on MRI in patients who have had multiple prior procedures; however, it is important to recognize various types of repairs such as urethral slings, which course through the retropubic space (Figs. 10A, B),62,63 sacrocolpopexy (Fig. 11),29 or vaginal mesh kits (Figs. 10C, D).64 Although a complete description of the various types of pelvic mesh and repair procedures is beyond the scope of this review, knowledge of the expected locations of the different repairs may facilitate identification of mesh and urethral tape as well as associated complications such as infection or erosions (Fig. 10). These complications may account for debilitating or chronic pelvic pain, which can have significant impact on quality of life in these patients. Magnetic resonance imaging can also identify other complications such as retropubic hematomas after urethral sling placement, which may not be apparent on physical examination.65
FUNCTIONAL EVALUATION
FIGURE 5. A 46-year-old gravida 3 para 2 female with prior hysterectomy and anterior vaginal wall suspension presenting with posterior bulge and suspected rectocele. Axial T2-weighted TSE image at the level of the puborectalis demonstrates lateral deviation and scarring of the anterior portions of the puborectalis muscle bilaterally (dark arrows), giving a “batwing” type appearance. The vagina has lost its normal H-shape, and there is posterior drooping of the lateral vagina on either side (dashed arrows). ©2014 Lippincott Williams & Wilkins
Functional evaluation is based on a 3-compartment model of the pelvic floor: anterior, middle or apical, and posterior compartment.24,40,66 Although different landmarks and reference lines have been proposed in the literature to evaluate prolapse,67 we utilize the PCL first introduced by Yang et al.68 Different authors have used slightly varied definitions of the PCL. We define the PCL as a line connecting the inferior tip of the pubic symphysis to the last nonmobile sacrococcygeal/coccygeal joint as discussed earlier (Fig. 7). The PCL demarcates the level of the levator plate. Another commonly used reference line, the midpubic line (MPL) is defined as a line drawn along the longitudinal axis of the pubic symphysis and is thought to correspond to the level of the hymen.40 The choice of reference line should be based on consensus between radiologists and referring physicians as neither the PCL nor MPL has been shown to be clearly superior to the other, and neither has shown good agreement with clinical staging67,69,70; however, the PCL is currently the most commonly used reference www.topicsinmri.com
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FIGURE 7. A 69-year-old female with history of prior hysterectomy, complex takedown of vaginal wall suspension, and urethral sling for bladder outlet obstruction, presenting with recurrent vaginal bulge for 6 months. Sagittal T2-weighted TSE image (A) shows insertion of the levator plate (arrow) spanning multiple segments above the coccygeal tip (dashed arrow). Sagittal TrueFISP image through the midline pelvis at rest (B) and defecation (C) show the variation of a PCL drawn to the coccygeal tip (dashed line; dashed arrow) and the more consistent PCL drawn to the levator insertion (solid line; solid arrow).
line. Perpendicular measurements are made from the PCL to the lowest point of the bladder, vaginal apex or cervix, and anorectal junction during rest (Fig. 12A), maximal strain, and defecation (Fig. 12B). The degree of prolapse is graded relative to these lines on a midline sagittal image, and separate grading systems exist for the PCL and MPL. We use the rule of 3’s for grading organ prolapse relative to the PCL (Table 2).40 At this time, the grading is a practical strategy that ultimately will require further research for validation of its clinical relevance. In addition to grading organ prolapse relative to the PCL, we grade pelvic floor relaxation using the “HMO” system (Fig. 12). The H or “hiatus” line is a measure of widening of the pelvic floor hiatus and is drawn from the inferior tip of the pubic symphysis to the posterior mucosa of the anorectal junction. The anorectal junction is delineated by the impression of the puborectalis muscle on the rectum, which can be identified on the sagittal images by
cross-referencing on axial images. The M-line is a measure of rectal descent and is defined as a line drawn in perpendicular fashion from the PCL down to the posterior tip of the H-line. The H-line and M-line measure up to 5 to 6 cm and 2 cm at rest, respectively. Excessive widening and descent of the pelvic floor, termed the descending perineum syndrome, can be graded based on the lengths of these lines during defecation (Table 3).40,66 During pelvic floor contraction, there may be diminished elevation of the levator plate in patients with descending perineal syndrome.71 The levator plate may be caudally angulated at rest, suggesting loss of posterior support.72 Causes of descending perineal syndrome include dysfunction of the pudendal nerve (eg, trauma, neuropathy) and chronic straining during defecation. Patients often present with diffuse or focal asymmetry of the levator muscles, which may be best observed in the coronal plane, and often complain of incomplete
FIGURE 8. A 61-year-old female with pelvic pressure symptoms and clinically suspected cystocele and cervical prolapse. Axial T2-weighted TSE image at the level of the pubic symphysis at rest (A) demonstrates bilateral drooping of the posterior bladder wall (“saddlebag sign”) suggestive of paravaginal defects in the endopelvic fascia. Axial T2-weighted TSE image in a 54-year-old female with clinically suspected rectocele just above the level of the pubic symphysis at rest (B) demonstrates a normal-appearing straight posterior bladder wall (arrows) for comparison in this patient without paravaginal defects.
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FIGURE 9. A 65-year-old female with urinary incontinence, rectocele, and defecatory dysfunction. Sagittal TrueFISP image through the midline pelvis during attempted defecation demonstrates high signal intensity within a dilated proximal urethral lumen consistent with funneling (arrow).
rectal emptying. Incomplete rectal emptying further propagates increased straining, thus worsening the condition, and can eventually lead to incontinence. Although descending perineal syndrome typically affects the posterior compartment, it can involve multiple
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compartments, frequently presenting with diffuse perineal bulge and discomfort.66,71 Measurement of the anorectal angle is another key component in functional evaluation of the pelvic floor. The anorectal angle is formed at the anorectal junction between the posterior border of the rectum and the anus. Under normal circumstances, the angle widens during defecation and narrows during Kegel; however, wide ranges of normal values have been reported. This may in part be due to the slightly varied techniques used by different authors to measure the angle.20,24,40,59,66,73 Variability in measurement may also be related to difficulty in identification of appropriate landmarks and is particularly problematic in fluoroscopic studies in comparison to MRI.74 Although traditionally, the anorectal angle is measured between the posterior rectal wall and the anus, some authors use the center of the rectal cavity. We have often noted distortion or bulging of the posterior rectal wall during defecation (Fig. 13) that, in our opinion, precludes adequate functional assessment of levator muscle function. Thus, in order to accurately classify levator contraction or relaxation, we measure an angle between a line along the levator plate and the central axis of the anus (Fig. 13). Although the resting anorectal angle may range between 108 and 127 degrees with changes of 15 and 20 degrees in either direction during Kegel and defecation,66 given the high variability discussed and lack of established normal values for an angle between the levator plate and anal canal to our knowledge, we place more emphasis on appropriate qualitative changes (narrowing during Kegel and widening during defecation) rather than the absolute values. Other authors have suggested measuring the angle of the levator plate relative to the PCL with an angle of more than
FIGURE 10. A 54-year-old female with prior suburethral tape and vaginal mesh placement presented with pain, dyspareunia, and urgency. Axial (A) and coronal (B) T2-weighted TSE images confirm presence of suburethral tape (solid arrows). Axial T2-weighted TSE image at the level of the vaginal apex (C) demonstrates thickened band-like tissue inseparable from the wall of the vagina (long dashed arrow) extending to the left pelvic sidewall (short dashed arrow), which was confirmed vaginal mesh with erosion at time of surgery. There was also localized mesh infection at surgery, which may account for the asymmetric thickening of the mesh on the left, although erosion and infection can be difficult to predict prospectively on imaging. Right side of the mesh was significantly thinner and poorly seen (black arrows in D). ©2014 Lippincott Williams & Wilkins
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FIGURE 11. A 65-year-old female with incontinence and pelvic pain after pelvic mesh and urethral sling placement. Sagittal T2-weighted TSE image (A) to the right of midline demonstrates normal-appearing sacrocolpopexy mesh (arrows) extending cranially from the vaginal apex. Coronal T2-weighted TSE image (B) through the central pelvis demonstrates normal appearing sacrocolpopexy mesh (arrows) extending cranially from the vaginal apex with expected rightward curvature.
10 degrees, suggesting loss of pelvic floor support.75 The decision of which angle to measure should be based on a consensus between radiologists and referring physicians, until firm data are available. When describing abnormalities in the various compartments, as indicated below, it is important to make note of the degree of defecatory effort made by the patient during the examination and provide such information in the final report. No or minimal defecation may be pathologic in itself (as described under posterior compartment abnormalities); however, inadequate effort during attempted defecation may underestimate the degree of prolapse.
indicate cystocele formation. A cystocele is defined as greater than 1-cm descent of the bladder floor (lowest portion of the bladder) below the PCL68 (Fig. 12) and can be graded by the rule of 3’s relative to the PCL (Table 2). Dynamic MRI has high sensitivity (100%) and positive predictive value (97%) for cystocele,76 and supine MRD actually shows larger degrees of cystocele than standing VCUG.35 Large cystoceles may efface the anterior vaginal wall resulting in complete eversion of the vagina. A myriad of surgical techniques have been used to repair cystoceles with varying success and complication rates.77
Anterior Compartment
Urethral Hypermobility
Cystoceles Patients with anterior compartment abnormalities often present with bulging along the anterior vaginal wall, which may
Cystoceles are often accompanied by urethral hypermobility. Urethral hypermobility occurs when there is rotation of the urethra into the horizontal plane and is defined as increase in urethral angle of at least 30 degrees based on VCUG and the “Q-tip” test.14,78,79
FIGURE 12. A 46-year-old female with chronic pelvic pain, demonstrating multi-compartment prolapse during defecation. Sagittal T2-weighted TSE images at rest (A) and sagittal TrueFISP image during defecation (B), both through the midline pelvis, demonstrate measurements of the bladder base (dotted white line) and vaginal apex (dashed white line) relative to the PCL (solid black line). The H-line (dotted black line) is drawn from the inferior tip of the pubic symphysis to the posterior mucosa of the anorectal junction. The M-line (dashed black line) is drawn from the posterior tip of the H-line to the PCL.
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TABLE 2. Grading of Pelvic Organ Prolapse Relative to PCL38 Grade
Perpendicular Distance Caudal to PCL
Mild Moderate Severe
6 cm
We measure urethral angle on MRI according to the previously reported method on VCUG between the urethral axis (facilitated if high signal is seen in the urethral lumen) and a vertical line drawn along the posterior/inferior margin of the pubic symphysis14 (Fig. 14). The urethral axis may not be as well demarcated on MRI as VCUG because of absence of Foley catheter. Furthermore, because the urethra can sometimes be curved at rest, and the lumen may not always be evident on the images, the urethral axis can be defined as a straight line connecting the internal meatus and external meatus. If the internal urethral meatus is anterior to the vertical reference line on sagittal image, the angle is considered negative (Fig. 14C). If the internal urethral meatus is posterior to the vertical line on sagittal image, the angle is considered positive (Fig. 14A). Urethral angles typically increase (more positive) with strain and defecation. Changes in urethral angle can be used as a measure of outcome after repair.14 Urethral hypermobility results from loss of periurethral support (level III endopelvic fascia support) and has been correlated with more global laxity of the pelvic floor.80 Causes of urethral hypermobility include pudendal nerve dysfunction, prior surgery, muscular or fascia defects, or weakness related to trauma or aging, prior pregnancy, vaginal delivery, and obesity.22,59 Urethral hypermobility can lead to stress incontinence, which may be seen as high signal intensity in the urethral lumen on T2-weighted images. Stress urinary incontinence can also result from intrinsic dysfunction of the urethral sphincter. Urethral funneling, seen as shortening of the urethra with abnormal dilatation and patency of the proximal lumen (Fig. 9), may indicate weak anatomic support and intrinsic sphincter deficiency in patients with incontinence81; however, it is nonspecific as it can be seen in 50% of postmenopausal continent women as well.79 Although the presence of urethral hypermobility in incontinent patients may alter surgical approach, the significance of borderline urethral mobility in clinically unsuspecting patients remains to be seen, and there may be overlap in urethral mobility between symptomatic and asymptomatic women. We have found that most females tend to have some degree of at least borderline urethral hypermobility; however, our experience may be biased because of institutional referral patterns as the majority of our patient population presents with anterior compartment complaints.
Bladder Outlet Obstruction Bladder outlet obstruction is an additional abnormality in the anterior compartment that most commonly follows surgical repair
TABLE 3. Grading of Pelvic Relaxation Using H-Line and M-Line as Measured During Maximal Straining or Defecation38,63 Stage 0 (Normal) 1 (Mild) 2 (Moderate) 3 (Severe)
H-Line, cm
M-Line, cm
Magnetic Resonance Imaging of Pelvic Floor Disorders Gaurav Khatri, MD Abstract: Physical examination alone is often inadequate for evaluation of pelvic floor dysfunction. Magnetic resonance imaging (MRI) is a robust modality that can provide high-quality anatomic and functional evaluation of the pelvic floor. Although lack of standardized technique and radiologist inexperience may be relative deterrents in universal acceptance of pelvic floor MRI, the role of MRI is increasing as it is technically feasible on most magnets and offers some advantages over the traditional fluoroscopic defecography. This review focuses on the technical and interpretational aspects of anatomic and functional pelvic floor MRI. Key Words: MR defecography, dynamic MRI, pelvic organ prolapse, pelvic floor MRI, pelvic floor mesh (Top Magn Reson Imaging 2014;23: 259–273)
P
elvic floor disorders are a complex set of conditions including pelvic organ prolapse, chronic pelvic pain, defecatory dysfunction, and urinary and fecal incontinence. An estimated nearly 1 in 4 women in the United States report symptoms of at least 1 pelvic floor disorder,1 and 75% of affected women report moderate to severe negative effect on their quality of life.2 The lifetime risk of undergoing a single surgical procedure for prolapse or incontinence by the age of 80 years is 11.1%3 with more than 200,000 annual surgical procedures in the United States.4,5 This likely represents but a fraction of women who suffer from pelvic floor disorders as many are managed nonsurgically or never actually present for clinical evaluation. Furthermore, the reoperation rate for recurrent prolapse is as high as 29%, implying a high rate of surgical failure.3 Direct surgical costs for pelvic floor dysfunction in the United States are reported to be more than $1 billion annually.4,6 The development of pelvic floor disorders is a multifactorial process, given the complex anatomy and function of the involved structures. Risk factors include advanced age, pregnancy and childbirth, hysterectomy, connective tissue abnormalities, injury to or denervation of pelvic floor musculature, obesity, smoking, and other conditions associated with chronically increased intra-abdominal pressure. In most cases, multiple compartments (anterior, middle, and posterior) of the pelvic floor are involved.7–11 Inadequacy of physical examination as the sole evaluation of the pelvic floor12,13 may be a contributing factor to the high surgical failure rate. Radiological evaluation of the pelvic floor has traditionally been performed with conventional fluoroscopic studies. A standing voiding cystourethrogram (VCUG) is a reproducible test to evaluate bladder and urethral mobility14; however, it does not provide information regarding the middle and posterior compartments. Dynamic cystocolpoproctography (DCP) has been routinely used for a more global functional assessment of pelvic floor dysfunction for a number of years15; however, it involves exposure to radiation and does
From the Department of Radiology, University of Texas Southwestern Medical Center, Dallas, TX. Reprints: Gaurav Khatri, MD, 5323 Harry Hines Blvd, Dallas, TX 75390 (e‐mail: [email protected]). The author declares no conflict of interest. Supplemental digital contents are available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s Web site (www.topicsinmri.com). Copyright ©2014 by Lippincott Williams & Wilkins
not allow for direct visualization of pelvic anatomy or structures. Magnetic resonance defecography (MRD) has evolved over the years as a potential alternative to DCP. Despite variations in MRD technique and wide range of “normal” findings in asymptomatic individuals,16,17 given its superior contrast resolution and multiplanar capabilities that enable direct visualization of pelvic floor anatomy and defects without exposure to radiation,18 MRD has developed as an important tool. Furthermore, MRD allows for global evaluation of the entire pelvis to depict prolapse in multiple compartments. In 1 study of patients with fecal incontinence, MRD influenced choice of surgical treatment in 67% of patients.9 Although some degree of prolapse has been reported on magnetic resonance imaging (MRI) in asymptomatic individuals, the degree of prolapse is generally greater in symptomatic patients.8 Furthermore, fluoroscopic defecography, which has traditionally been used for functional evaluation of the pelvic floor, also suffers from similar variability of findings in asymptomatic subjects.19,20 High costs, limited radiologist experience, and/or expertise in interpretation, as well as questions about reproducibility of pelvic measurements on dynamic MRI,21 are additional deterrents to universal acceptance of MRI for evaluation of the pelvic floor. This review focuses on the utility of MRI for anatomic as well as functional evaluation of the pelvic floor in order to address some of these limitations.
PELVIC FLOOR ANATOMY A brief review of the female pelvic floor anatomy is helpful to understand the complex nature of the problem because majority of functional pelvic floor disorders occur in women. The pelvic floor can be divided into 3 compartments. The anterior compartment contains the urinary bladder and urethra; the middle compartment refers to the uterus, cervix, and vagina; and the posterior compartment comprises the rectum and anal canal. Abnormalities in 1 compartment are frequently associated with dysfunction of other compartments.7,8 The compartments of the pelvic floor are supported by complex interplay of muscular, fascial, and ligamentous attachments to the pelvic skeleton. Fascial and ligamentous attachments of the pelvic floor comprise the passive support system, whereas the muscles of the pelvic floor are involved in active support. The 3 layers of the pelvic floor support structures include the endopelvic fascia most superiorly, the pelvic diaphragm in the middle, and the urogenital diaphragm most inferiorly.22–24 The endopelvic fascia is a layer of connective tissue that lines the pelvic floor, extending in a sheet-like fashion from the bony pelvis to cover the levator ani muscles and pelvic viscera. It is difficult to perceive on imaging. Various portions of the fascia are labeled according to their locations including the pubocervical fascia (between the bladder and vagina/cervix), rectovaginal fascia (between the vagina and rectum), parametrium (extending from the cervix to the pelvic sidewall), and paracolpium (extending from the vagina to the pelvic sidewall). Superiorly, prominent folds of the fascia form the cardinal and uterosacral ligaments. Lateral condensations of the fascia coalesce to form the arcus tendineus, which acts as a lateral support structure for the pelvic organs. The levator ani muscles as well as the pubocervical and rectovaginal fasciae insert upon the arcus tendineus laterally. Direct visualization of arcus tendineus is difficult because of its small size; its location can be inferred from the angle formed between the levator
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ani muscles and surface of the internal oblique muscles.23–25 The endopelvic fascia provides 3 levels of support of the pelvic floor based on its location: level I, the upper third of the vagina; level II, the middle third of the vagina; level III, lower third of the vagina.26 The pelvic diaphragm is well seen on imaging and consists of the levator ani muscles and the coccygeus (also known as ischiococcygeus) muscle. The puborectalis, pubococcygeus, and ileococcygeus muscles comprise the levator ani. This group of hourglass-shaped muscles forms the floor of the pelvis (Fig. 1A). They attach laterally to the arcus tendineus and come together centrally and posteriorly into a condensation of tissue called the levator plate, which inserts onto the sacrococcygeal joints. The puborectalis muscle, the most caudal of the levator ani muscles, is a sling-like or “U”-shaped muscle that arises anteriorly from the pubic symphysis and wraps around the anorectum (Fig. 1B). The impression of the puborectalis demarcates the anorectal junction (Fig. 1C). The pubococcygeus arises predominantly from the superior rami of the pubic symphysis anteriorly and inserts upon the levator plate posteriorly. It also has attachments upon the vagina, rectum, and perineal body, and its fibers overlap in a slinglike fashion with the puborectalis muscle. The pubococcygeus and puborectalis muscle are sometimes collectively referred to as the pubovisceralis muscle. The ileococcygeus is a thinner flat muscle more cranially that arises from the arcus tendineus laterally and inserts upon the levator plate posteriorly. The coccygeus muscle is a smaller component of the pelvic diaphragm that extends on either side from the ischial spine to the midline coccyx. It sits posterior to the ileococcygeus and covers the sacrospinous ligament.27 The pelvic diaphragm muscles provide constant passive tone to the pelvic floor, but also work in unison to actively tighten or relax the pelvic floor. The urogenital or levator hiatus is a “U-shaped” opening in the pelvic floor lined by the levator muscles (Fig. 1B). The urethra, vagina, and rectum pass through the hiatus, and widening of the hiatus results in pelvic organ prolapse. The average width of the levator hiatus in asymptomatic females is approximately 4 cm.28 The final and most caudal layer of the pelvic floor support structures is the urogenital diaphragm, also called the perineal membrane (Fig. 1A). This membrane is formed from primarily the deep transverse peroneus muscle as well as condensation of
connective tissue that extends horizontally from the ischium on either side to the perineal body in the midline with attachment anteriorly to the pubic symphysis, thus yielding a triangular shape. The perineal body is a connective tissue support structure located in the perineum between the anal verge and vaginal introitus. It is also called the central tendon of the perineum and is a site of attachment for multiple pelvic floor structures.23,24
MRI TECHNIQUE Because of the complex multicompartmental nature of pelvic floor disease, adequate evaluation requires both superior anatomic and functional imaging. Magnetic resonance imaging of the pelvic floor allows for dynamic evaluation of all compartments of the pelvic floor in a relatively noninvasive manner and without exposure to radiation. It provides multiplanar imaging, which can be of great utility when assessing the complex pelvic floor anatomy, particularly in postsurgical cases. Images with high spatial and soft tissue contrast resolution allow for direct visualization of the pelvic floor support structures and/or anatomic defects that may guide or alter management decisions,27 whereas the high temporal resolution allows for dynamic evaluation during straining and defecation. In cases of prior surgical intervention, MRI of the pelvic floor may help identify and evaluate previously placed mesh material and associated complications.29 An added benefit of MRI is detection of incidental or associated abnormalities in the pelvis, which may contribute to pelvic floor dysfunction (Fig. 2). Dynamic pelvic floor can be performed in an open magnet with the patient sitting upright, or in a conventional closed MRI unit with the patient supine. The sitting position may theoretically be more physiologic for studying the pelvic floor; however, the relative inaccessibility of open MRI units makes upright imaging less feasible and less reproducible across institutions. Gufler et al30 showed no significant difference in anterior and middle compartment prolapse between supine and upright colpocystoproctography and supine dynamic MRI in a small series of patients; however, the study was performed with strain rather than defecation. Another study comparing supine MRI during straining to sitting magnetic resonance (MR) with defecation found decreased sensitivity of the supine examination for rectal intussusception and bladder descent31;
FIGURE 1. A 46-year-old female with chronic pelvic pain. Coronal T2-weighted TSE image through the rectum (A) demonstrates the symmetric hourglass shape of the levator ani muscles at rest (dashed arrows) with upward convexity. The urogenital diaphragm or perineal membrane (solid arrows) is seen extending horizontally from the midline to the ischium on either side. Axial T2-weighted TSE image (B) at the level of the pubic symphysis demonstrates relatively symmetric “U-shaped” appearance of the puborectalis sling (arrows) outlining the urogenital or levator hiatus. The urethra (u), vagina (v), and rectum (r) are seen from anterior to posterior within the hiatus. Note the normal attachment of the puborectalis anteriorly upon the pubic bone (dashed arrows). Sagittal T2-weighted TSE image (C) to the left of midline shows the horizontally oriented puborectalis muscle, which can be used as a landmark to delineate the anorectal junction. A Bartholin’s gland cyst is incidentally seen (asterisk).
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FIGURE 2. A 43-year-old female with history of prior pelvic mass resection presenting with defecatory dysfunction. Coronal T2-weighted TSE image (A) demonstrates intermediate signal intensity tissue (arrows) in the left ischioanal fossa causing a defect in the levator muscles. The gel-filled rectum is seen herniating laterally through the defect (asterisk). Sagittal T2-weighted TSE image slightly to the left of midline (B) shows the large confluent pelvic mass, a pathologically confirmed recurrent aggressive angiomyxoma (arrows) extending below the level of the urethra, as well as posteriorly in the ischiorectal fossa. The rectum (asterisk) demonstrates downward herniation through the pelvic floor defect at rest. On axial T2-weighted TSE image (C), the mass (arrows) is seen to obliterate the left levator muscles, producing a lateral defect for herniation of the rectum (asterisk) even at rest. This lateral rectocele increased in size during attempts at evacuation (not shown), resulting in the defecatory dysfunction.
however, lack of a defecation phase during supine MRI in that study confounds these findings. The defecation phase is imperative to adequate dynamic evaluation of the pelvic floor on MRI during upright32 and supine imaging.33 Kelvin et al34 did demonstrate that supine MR with defecation underestimates the extent of cystoceles and enteroceles relative to sitting DCP; however, to our knowledge, adequate comparisons of MR with defecation in supine position to MR with defecation in sitting position are lacking in the scientific literature. In our experience, supine MR defecography actually shows higher degrees of anterior compartment prolapse compared with upright VCUG.35 Furthermore, closed magnet systems used for supine MRD are of higher field strength and thus allow more detailed anatomic evaluation of the pelvic floor. Open magnets used for upright MRI suffer from lower signal-to-noise and relatively poor soft tissue resolution.36 We perform MRD in the supine position in a closed magnet at our institution. Given the unique nature of the examination, it is imperative to explain the procedure to the patient prior to arrival to avoid undue anxiety and embarrassment during the examination. We also suggest that the patient perform fleets enema prior to arrival to the department in order to clear the rectum, although this is not mandatory. Overdistention of the bladder can obscure prolapse in other compartments because of mass effect34,37; however, an empty bladder may limit evaluation of anterior compartment prolapse. Hence, the patient is asked to urinate upon arrival to the department and then drink 16 oz of water in an effort to attain some bladder distention in a noninvasive manner (ie, without placement of Foley catheter to drain or distend the bladder). The technologist reviews the procedure in detail; explains the Kegel (squeeze), Valsalva (strain), and defecation maneuvers to the patient; and addresses any concerns that patient may have regarding defection on the table prior to placing them in the magnet. The MRI table is covered with disposable absorbent pads. The patient is placed in lateral decubitus position within an inflatable MR-safe barium enema ring, and ultrasound gel (off-label use) is instilled in the rectum via a long catheter-tip syringe. The patient is then placed in supine position within the enema ring. The benefit of rectal contrast for MR defecography has been established previously38; however, the exact composition and volume of contrast media to be instilled in the rectum have been debated with different authors, ©2014 Lippincott Williams & Wilkins
suggesting a variety of substances including some thickened with potato starch to mimic the consistency of stool.39–41 We have encountered false negatives for prolapse (enteroceles) on MRI because of rectal (over)distention to 180 mL. Thus, based on a study at our institution, which showed a lower volume of 120 mL of gel to be as effective as 180 mL for inducing successful defecation,42 we routinely use 120 mL of intrarectal gel for our protocol. Once the patient has been prepared, T2-weighted turbo spin echo (TSE) sequences in axial, coronal, and sagittal planes as well as a T1-weighted sequence in the axial plane are acquired at rest. Functional imaging involves acquiring cine-type TrueFISP (true fast imaging with steady-state precession) images during dynamic maneuvers. TrueFISP acquisition demonstrates greater degree of prolapse in all 3 compartments than the HASTE (half-Fourier acquisition single-shot TSE) acquisition43 and is preferred for the cine imaging. The initial cine images are obtained through a single midline sagittal plane (which includes the pubic symphysis, urethra, vagina, anal canal, levator plate, and coccyx) during Kegel maneuver and then during defecation. The sagittal midline cine acquisition is repeated with defection if the patient is unable to evacuate on the initial attempt. We then obtain additional cine acquisitions in the coronal oblique plane (single slice angled through anal canal) as well as axial oblique plane along a line connecting the bottom of pubic symphysis and tip of the coccyx during additional defecation or maximal strain (if rectum is already empty) in an effort to visualize lateral defects that may not be readily visible on midline sagittal images. A final sagittal midline cine sequence (“postdefecation Valsalva”) is performed during maximal strain. Finally, we perform an additional axial high-resolution T2-weighted TSE for evaluation of the pelvic floor anatomy as muscle or anatomic defects may be more apparent immediately after strain or after defecation. Our institutional MRD protocol is detailed in Table 1.
MRI INTERPRETATION In our practice, we utilize a data collection sheet (Appendix 1, http://links.lww.com/TMRI/A8) to facilitate systematic interpretation and minimize variation between readers. We report findings using a dictation template (Appendix 2, http://links.lww.com/TMRI/A9) to ensure organization and consistency in reporting and grading of key findings in a manner agreed upon with our referring www.topicsinmri.com
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TABLE 1. Institutional MR Defecography Protocol Sequence
Imaging Plane
Maneuver
T2 TSE Axial Rest T2 TSE Sagittal Rest T2 TSE Coronal Rest T1 SE Axial Rest Cine TrueFISP Sagittal Kegel Cine TrueFISP Sagittal Defecation Cine TrueFISP Axial oblique Defecation Cine TrueFISP Coronal oblique Defecation Cine TrueFISP Sagittal Postdefecation Valsalva T2 TSE Axial Rest
Field of Slice Thickness, Repetition Time to Flip Angle, View, cm mm time, ms Echo, ms Degrees 26 26 26 26 34 34 33 33 34 26
physicians. These tools maximize efficiency and completeness in both anatomic and functional interpretation of pelvic floor MRI.
ANATOMIC EVALUATION Interpretation of the pelvic floor MRI should begin with an assessment of the anatomic structures as morphologic changes to these structures have been correlated with functional abnormalities of the pelvic floor.44,45 Although there is variability in the appearance of the pelvic support structures even in asymptomatic nulliparous women,46 significant differences in levator muscle volume, shape, and integrity have been shown between asymptomatic individuals and those with incontinence and pelvic prolapse.47 The levator muscles should be assessed for areas of asymmetric thickening or atrophy (Fig. 3), focal defects, scarring, ballooning (Fig. 4), or focal eventration on different planes of imaging.48 Identification of these anatomic abnormalities may predict the pattern of prolapse on the functional images. Care must be taken when evaluating the puborectalis muscle as it is often thinner on the right even in asymptomatic women when viewed in the axial plane, with thickness at the level of the proximal-middle urethra ranging from 2 to 5 mm on the right and 4 to 7 mm on the left.28,49 Anatomic defects of the puborectalis muscle are seen as lateral deviations anteriorly at the attachment site to the pubic bone50; can be unilateral or bilateral (resulting in a “batwing” appearance) (Fig. 5); may be secondary to trauma during vaginal delivery, episiotomy, or other vaginal surgery; and may predict subsequent pelvic floor
5 5 5 5 8 8 8 8 8 5
3920 4070 5120 625 734.4 734.4 742.6 946.4 734.4 3920
91 91 91 10 1.8 1.8 1.8 1.8 1.8 91
150 150 150 180 80 80 80 80 80 150
Matrix 320 256 320 256 320 256 256 192 256 256 256 256 256 256 256 256 256 256 320 256
dysfunction.51–54 Grading scales for these defects have been proposed.55,56 The anal sphincter complex must also be evaluated. The internal anal sphincter is seen as a thick circular muscle layer with variable hypointense or intermediate signal intensity on axial T2weighted images, whereas the external anal sphincter is seen as a thinner circumferential band of hypointense signal intensity (Fig. 6). It is important to note the integrity of the levator plate and its level of insertion upon the sacrum/coccyx (Fig. 7). The insertion of the levator plate may vary between individuals, and often the insertion may span multiple coccygeal segments with a dominant inserting band usually identifiable in most cases. There is also a certain mobility of the coccyx that occurs during defecation57,58 (Figs. 7B, C). Using the coccygeal tip as the posterior point of reference for the pubococcygeal line (PCL) has vulnerability to naturally occurring positional changes of the coccyx during the study. Therefore, we advocate using the last nonmobile coccygeal or sacrococcygeal joint. We have found that this often correlates with the dominant insertion of the levator plate. We document these anatomic landmarks in our report (Appendix 2, http://links.lww.com/TMRI/A9) in order to maintain reproducibility in interpretation. Morphologic assessment of the urethra and vagina is also important as abnormalities may suggest location of pelvic floor defects. A level I fascia defect, which results from detachment of the upper vagina from the uterosacral ligament, results in sagging of the vagina bilaterally (“chevron sign”).59,60 Deficiency in level II endopelvic fascial support of the middle third of the vagina combined with defects in the puborectalis muscle may result in
FIGURE 3. A 75-year-old female with remote history of multicompartment pelvic floor repair with recurrent prolapse. Axial T2-weighted TSE image at level of puborectalis muscle (A) shows asymmetry and absence of muscles on right (dashed arrow) due to complete tear. Left puborectalis muscle thickness is preserved (arrow). Coronal T2-weighted TSE image (B) shows asymmetric bulging of rectum on the right with absence/atrophy of the right puborectalis (dashed arrow). Left puborectalis is seen on end (arrow).
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FIGURE 4. A 70-year-old female with history of constipation. Axial T2-weighted TSE image at the level of the pubic symphysis demonstrates ballooning of puborectalis bilaterally (arrows).
disruption of the expected “H” or hammock shape of the vagina on axial images in patients with prolapse49 (Fig. 5); however, the vagina may have variable shape on imaging even in asymptomatic females.28 A lateral level II defect (paravaginal defect) on either side may result in posterior drooping of the posterior bladder wall on the affected side (“saddlebag sign”)59,60 (Fig. 8). Level III endopelvic fascia defects may involve disruption of the urethral suspension ligaments and resultant widening of the retropubic space (“mustache sign”).59,60 Although the normal circular target appearance of the urethra may become less distinct in postmenopausal females, flattening or funneling of the urethra (Fig. 9) and disruption of surrounding support structures can be seen in the setting of urethral incontinence.59,61
MRI of Pelvic Floor Disorders
FIGURE 6. A 62-year-old female with incontinence and prolapse symptoms. Axial T2-weighted TSE image just above the anal verge demonstrates thick circular internal anal sphincter (arrows). The thinner external anal sphincter muscle is seen extending more posteriorly (dashed arrows).
Patients with pelvic floor dysfunction often present after previous attempts at native tissue repair and/or synthetic pelvic mesh and tape placements. Identification of postsurgical changes and potential mesh and tape remnants is an important part of the anatomic evaluation. These postsurgical changes and mesh cannot be directly visualized on DCP. Differentiation of mesh from granulation or postsurgical fibrosis can often also be difficult on MRI in patients who have had multiple prior procedures; however, it is important to recognize various types of repairs such as urethral slings, which course through the retropubic space (Figs. 10A, B),62,63 sacrocolpopexy (Fig. 11),29 or vaginal mesh kits (Figs. 10C, D).64 Although a complete description of the various types of pelvic mesh and repair procedures is beyond the scope of this review, knowledge of the expected locations of the different repairs may facilitate identification of mesh and urethral tape as well as associated complications such as infection or erosions (Fig. 10). These complications may account for debilitating or chronic pelvic pain, which can have significant impact on quality of life in these patients. Magnetic resonance imaging can also identify other complications such as retropubic hematomas after urethral sling placement, which may not be apparent on physical examination.65
FUNCTIONAL EVALUATION
FIGURE 5. A 46-year-old gravida 3 para 2 female with prior hysterectomy and anterior vaginal wall suspension presenting with posterior bulge and suspected rectocele. Axial T2-weighted TSE image at the level of the puborectalis demonstrates lateral deviation and scarring of the anterior portions of the puborectalis muscle bilaterally (dark arrows), giving a “batwing” type appearance. The vagina has lost its normal H-shape, and there is posterior drooping of the lateral vagina on either side (dashed arrows). ©2014 Lippincott Williams & Wilkins
Functional evaluation is based on a 3-compartment model of the pelvic floor: anterior, middle or apical, and posterior compartment.24,40,66 Although different landmarks and reference lines have been proposed in the literature to evaluate prolapse,67 we utilize the PCL first introduced by Yang et al.68 Different authors have used slightly varied definitions of the PCL. We define the PCL as a line connecting the inferior tip of the pubic symphysis to the last nonmobile sacrococcygeal/coccygeal joint as discussed earlier (Fig. 7). The PCL demarcates the level of the levator plate. Another commonly used reference line, the midpubic line (MPL) is defined as a line drawn along the longitudinal axis of the pubic symphysis and is thought to correspond to the level of the hymen.40 The choice of reference line should be based on consensus between radiologists and referring physicians as neither the PCL nor MPL has been shown to be clearly superior to the other, and neither has shown good agreement with clinical staging67,69,70; however, the PCL is currently the most commonly used reference www.topicsinmri.com
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FIGURE 7. A 69-year-old female with history of prior hysterectomy, complex takedown of vaginal wall suspension, and urethral sling for bladder outlet obstruction, presenting with recurrent vaginal bulge for 6 months. Sagittal T2-weighted TSE image (A) shows insertion of the levator plate (arrow) spanning multiple segments above the coccygeal tip (dashed arrow). Sagittal TrueFISP image through the midline pelvis at rest (B) and defecation (C) show the variation of a PCL drawn to the coccygeal tip (dashed line; dashed arrow) and the more consistent PCL drawn to the levator insertion (solid line; solid arrow).
line. Perpendicular measurements are made from the PCL to the lowest point of the bladder, vaginal apex or cervix, and anorectal junction during rest (Fig. 12A), maximal strain, and defecation (Fig. 12B). The degree of prolapse is graded relative to these lines on a midline sagittal image, and separate grading systems exist for the PCL and MPL. We use the rule of 3’s for grading organ prolapse relative to the PCL (Table 2).40 At this time, the grading is a practical strategy that ultimately will require further research for validation of its clinical relevance. In addition to grading organ prolapse relative to the PCL, we grade pelvic floor relaxation using the “HMO” system (Fig. 12). The H or “hiatus” line is a measure of widening of the pelvic floor hiatus and is drawn from the inferior tip of the pubic symphysis to the posterior mucosa of the anorectal junction. The anorectal junction is delineated by the impression of the puborectalis muscle on the rectum, which can be identified on the sagittal images by
cross-referencing on axial images. The M-line is a measure of rectal descent and is defined as a line drawn in perpendicular fashion from the PCL down to the posterior tip of the H-line. The H-line and M-line measure up to 5 to 6 cm and 2 cm at rest, respectively. Excessive widening and descent of the pelvic floor, termed the descending perineum syndrome, can be graded based on the lengths of these lines during defecation (Table 3).40,66 During pelvic floor contraction, there may be diminished elevation of the levator plate in patients with descending perineal syndrome.71 The levator plate may be caudally angulated at rest, suggesting loss of posterior support.72 Causes of descending perineal syndrome include dysfunction of the pudendal nerve (eg, trauma, neuropathy) and chronic straining during defecation. Patients often present with diffuse or focal asymmetry of the levator muscles, which may be best observed in the coronal plane, and often complain of incomplete
FIGURE 8. A 61-year-old female with pelvic pressure symptoms and clinically suspected cystocele and cervical prolapse. Axial T2-weighted TSE image at the level of the pubic symphysis at rest (A) demonstrates bilateral drooping of the posterior bladder wall (“saddlebag sign”) suggestive of paravaginal defects in the endopelvic fascia. Axial T2-weighted TSE image in a 54-year-old female with clinically suspected rectocele just above the level of the pubic symphysis at rest (B) demonstrates a normal-appearing straight posterior bladder wall (arrows) for comparison in this patient without paravaginal defects.
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FIGURE 9. A 65-year-old female with urinary incontinence, rectocele, and defecatory dysfunction. Sagittal TrueFISP image through the midline pelvis during attempted defecation demonstrates high signal intensity within a dilated proximal urethral lumen consistent with funneling (arrow).
rectal emptying. Incomplete rectal emptying further propagates increased straining, thus worsening the condition, and can eventually lead to incontinence. Although descending perineal syndrome typically affects the posterior compartment, it can involve multiple
MRI of Pelvic Floor Disorders
compartments, frequently presenting with diffuse perineal bulge and discomfort.66,71 Measurement of the anorectal angle is another key component in functional evaluation of the pelvic floor. The anorectal angle is formed at the anorectal junction between the posterior border of the rectum and the anus. Under normal circumstances, the angle widens during defecation and narrows during Kegel; however, wide ranges of normal values have been reported. This may in part be due to the slightly varied techniques used by different authors to measure the angle.20,24,40,59,66,73 Variability in measurement may also be related to difficulty in identification of appropriate landmarks and is particularly problematic in fluoroscopic studies in comparison to MRI.74 Although traditionally, the anorectal angle is measured between the posterior rectal wall and the anus, some authors use the center of the rectal cavity. We have often noted distortion or bulging of the posterior rectal wall during defecation (Fig. 13) that, in our opinion, precludes adequate functional assessment of levator muscle function. Thus, in order to accurately classify levator contraction or relaxation, we measure an angle between a line along the levator plate and the central axis of the anus (Fig. 13). Although the resting anorectal angle may range between 108 and 127 degrees with changes of 15 and 20 degrees in either direction during Kegel and defecation,66 given the high variability discussed and lack of established normal values for an angle between the levator plate and anal canal to our knowledge, we place more emphasis on appropriate qualitative changes (narrowing during Kegel and widening during defecation) rather than the absolute values. Other authors have suggested measuring the angle of the levator plate relative to the PCL with an angle of more than
FIGURE 10. A 54-year-old female with prior suburethral tape and vaginal mesh placement presented with pain, dyspareunia, and urgency. Axial (A) and coronal (B) T2-weighted TSE images confirm presence of suburethral tape (solid arrows). Axial T2-weighted TSE image at the level of the vaginal apex (C) demonstrates thickened band-like tissue inseparable from the wall of the vagina (long dashed arrow) extending to the left pelvic sidewall (short dashed arrow), which was confirmed vaginal mesh with erosion at time of surgery. There was also localized mesh infection at surgery, which may account for the asymmetric thickening of the mesh on the left, although erosion and infection can be difficult to predict prospectively on imaging. Right side of the mesh was significantly thinner and poorly seen (black arrows in D). ©2014 Lippincott Williams & Wilkins
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Khatri
FIGURE 11. A 65-year-old female with incontinence and pelvic pain after pelvic mesh and urethral sling placement. Sagittal T2-weighted TSE image (A) to the right of midline demonstrates normal-appearing sacrocolpopexy mesh (arrows) extending cranially from the vaginal apex. Coronal T2-weighted TSE image (B) through the central pelvis demonstrates normal appearing sacrocolpopexy mesh (arrows) extending cranially from the vaginal apex with expected rightward curvature.
10 degrees, suggesting loss of pelvic floor support.75 The decision of which angle to measure should be based on a consensus between radiologists and referring physicians, until firm data are available. When describing abnormalities in the various compartments, as indicated below, it is important to make note of the degree of defecatory effort made by the patient during the examination and provide such information in the final report. No or minimal defecation may be pathologic in itself (as described under posterior compartment abnormalities); however, inadequate effort during attempted defecation may underestimate the degree of prolapse.
indicate cystocele formation. A cystocele is defined as greater than 1-cm descent of the bladder floor (lowest portion of the bladder) below the PCL68 (Fig. 12) and can be graded by the rule of 3’s relative to the PCL (Table 2). Dynamic MRI has high sensitivity (100%) and positive predictive value (97%) for cystocele,76 and supine MRD actually shows larger degrees of cystocele than standing VCUG.35 Large cystoceles may efface the anterior vaginal wall resulting in complete eversion of the vagina. A myriad of surgical techniques have been used to repair cystoceles with varying success and complication rates.77
Anterior Compartment
Urethral Hypermobility
Cystoceles Patients with anterior compartment abnormalities often present with bulging along the anterior vaginal wall, which may
Cystoceles are often accompanied by urethral hypermobility. Urethral hypermobility occurs when there is rotation of the urethra into the horizontal plane and is defined as increase in urethral angle of at least 30 degrees based on VCUG and the “Q-tip” test.14,78,79
FIGURE 12. A 46-year-old female with chronic pelvic pain, demonstrating multi-compartment prolapse during defecation. Sagittal T2-weighted TSE images at rest (A) and sagittal TrueFISP image during defecation (B), both through the midline pelvis, demonstrate measurements of the bladder base (dotted white line) and vaginal apex (dashed white line) relative to the PCL (solid black line). The H-line (dotted black line) is drawn from the inferior tip of the pubic symphysis to the posterior mucosa of the anorectal junction. The M-line (dashed black line) is drawn from the posterior tip of the H-line to the PCL.
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MRI of Pelvic Floor Disorders
TABLE 2. Grading of Pelvic Organ Prolapse Relative to PCL38 Grade
Perpendicular Distance Caudal to PCL
Mild Moderate Severe
6 cm
We measure urethral angle on MRI according to the previously reported method on VCUG between the urethral axis (facilitated if high signal is seen in the urethral lumen) and a vertical line drawn along the posterior/inferior margin of the pubic symphysis14 (Fig. 14). The urethral axis may not be as well demarcated on MRI as VCUG because of absence of Foley catheter. Furthermore, because the urethra can sometimes be curved at rest, and the lumen may not always be evident on the images, the urethral axis can be defined as a straight line connecting the internal meatus and external meatus. If the internal urethral meatus is anterior to the vertical reference line on sagittal image, the angle is considered negative (Fig. 14C). If the internal urethral meatus is posterior to the vertical line on sagittal image, the angle is considered positive (Fig. 14A). Urethral angles typically increase (more positive) with strain and defecation. Changes in urethral angle can be used as a measure of outcome after repair.14 Urethral hypermobility results from loss of periurethral support (level III endopelvic fascia support) and has been correlated with more global laxity of the pelvic floor.80 Causes of urethral hypermobility include pudendal nerve dysfunction, prior surgery, muscular or fascia defects, or weakness related to trauma or aging, prior pregnancy, vaginal delivery, and obesity.22,59 Urethral hypermobility can lead to stress incontinence, which may be seen as high signal intensity in the urethral lumen on T2-weighted images. Stress urinary incontinence can also result from intrinsic dysfunction of the urethral sphincter. Urethral funneling, seen as shortening of the urethra with abnormal dilatation and patency of the proximal lumen (Fig. 9), may indicate weak anatomic support and intrinsic sphincter deficiency in patients with incontinence81; however, it is nonspecific as it can be seen in 50% of postmenopausal continent women as well.79 Although the presence of urethral hypermobility in incontinent patients may alter surgical approach, the significance of borderline urethral mobility in clinically unsuspecting patients remains to be seen, and there may be overlap in urethral mobility between symptomatic and asymptomatic women. We have found that most females tend to have some degree of at least borderline urethral hypermobility; however, our experience may be biased because of institutional referral patterns as the majority of our patient population presents with anterior compartment complaints.
Bladder Outlet Obstruction Bladder outlet obstruction is an additional abnormality in the anterior compartment that most commonly follows surgical repair
TABLE 3. Grading of Pelvic Relaxation Using H-Line and M-Line as Measured During Maximal Straining or Defecation38,63 Stage 0 (Normal) 1 (Mild) 2 (Moderate) 3 (Severe)
H-Line, cm
M-Line, cm
