Pelvic Floor Anatomy and Imaging

Home , Endoanal ultrasound, Hymen, Levator ani, Mons pubis, Neck, Pelvic cavity

Seminars in Colon and Rectal Surgery 27 (2016) 5–14

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Seminars in Colon and Rectal Surgery

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Pelvic ﬂoor anatomy and imaging

Giulio A. Santoro, MD, PhDa,n, Abdul H. Sultan, MB ChB, MD, FRCOGb a Head Pelvic Floor Unit, Department of Surgery, Regional Hospital, Piazzale Ospedale 1, Treviso 31100, Italy b Croydon University Hospital, Surrey, UK

abstract

The pelvic floor is a complex, three-dimensional mechanical apparatus that consists of several components: the pelvic organs and endopelvic fascia, the ligament and perineal membrane, the levator ani muscles and superficial perineal muscles, and the pelvic nerves. The support for the pelvic organs comes from connections to the bony pelvis and its attached muscles. Any damage to the structural and functional interactions of the pelvic floor elements can potentially cause multicompartmental dysfunction. Surgical management of pelvic floor disorders depends on a comprehensive understanding of the structural integrity and function of the pelvic floor. As a result of technological progress, dedicated imaging modalities including static and dynamic 3D and 4D transvaginal, endoanal and transperineal ultrasound, dynamic Magnetic Resonance, and evacuation proctography have been introduced. The “integrated” use of these techniques provides outstanding visualization of the anatomy of the pelvic floor, allowing for accurate assessment of the major disorders— urinary and fecal incontinence, pelvic organ prolapse, and obstructed defecation syndrome. & 2016 Elsevier Inc. All rights reserved.

Introduction only one compartment, 95% of these have abnormalities in all three compartments.2 Therefore, the specialist (urologist, gynecol- The pelvic floor is a complex, three-dimensional (3D) mechan- ogist, gastroenterologist, colorectal surgeon, or physical therapist) ical apparatus that has been artificially divided into three different needs to appreciate that as pelvic floor disorders rarely occur in regions (anterior, middle, and posterior compartments). In this isolation, evaluation and surgery can impact on the function of the article, the term “pelvic floor” is used broadly to include all the neighboring compartment.3,4 structures supporting the pelvic cavity rather than the restricted Diagnostic evaluation has a fundamental role to identify all use of this term to refer to the levator ani group of muscles. pelvic floor disorders and to provide comprehensive information The pelvic floor consists of several components lying between for a management that encompasses the consequences of therapy the peritoneum and the vulvar skin. From above downwards, these on adjacent organs and avoid sequential surgery. The increasing are the peritoneum, pelvic viscera and endopelvic fascia, levator availability of ultrasound equipment in the clinical setting, and the ani muscles, perineal membrane, and superficial genital muscles. recent development of 3D and 4D ultrasound, have renewed The support for all these structures comes from connections to the interest in using this modality to image pelvic floor anatomy as a bony pelvis and its attached muscles. The pelvic organs are often key to understanding dysfunction.5 The “integrated approach,” by thought of as being supported by the pelvic floor, but in reality using a combination of different modalities (endovaginal ultra- form part of it. The pelvic viscera play an important role in forming sound—EVUS, endoanal ultrasound—EAUS, and transperineal the pelvic floor through their connections with structures, such as ultrasound—TPUS) provides a comprehensive evaluation of this the cardinal and uterosacral ligaments and are attached to the region.5 In this article, we will also present the advantages and levator ani muscles when they pass through the urogenital hiatus. limitations of other imaging modalities such as evacuation proc- As a consequence, any dysfunction of the structural and functional tography and dynamic magnetic resonance imaging (MRI). interactions of the pelvic floor elements can potentially cause a multicompartmental disorder.1 Although patients may present with symptoms (urinary incontinence, voiding dysfuntion, fecal Pelvic floor anatomy incontinence, obstructed defecation, and dyssynergy) that involve The pelvic organ support system includes the endopelvic fascia, the perineal membrane, and the levator ani muscles that are n Corresponding author. controlled by the central and peripheral nervous system. The E-mail address: [email protected] (G.A. Santoro). supports of the uterus and vagina are different in different regions. http://dx.doi.org/10.1053/j.scrs.2015.12.003 1043-1489/& 2016 Elsevier Inc. All rights reserved.

Fig. 2. Uterosacral ligaments (USL) extend both vertically and also posteriorly toward the sacrum (S). Cardinal ligaments (CL) suspend the cervix (CX) from the lateral pelvic walls.

Fig. 1. Levels of vaginal support according to DeLancey. In level I (suspension) the also contains nerves and lymphatic channels. When placed under uterosacral and cardinal ligaments suspend the vagina from the lateral pelvic walls. tension, it assumes the appearance of a strong cable as the fibers In level II (attachment) the vagina is attached to the arcus tendineus fasciae pelvis align along the lines of tension. It originates from the pelvic and the superior fascia of levator ani by the pubocervical (PCF) and rectovaginal fascia (RVF). In level III (distal support) the vagina is attached directly to the sidewall and inserts on the uterus, cervix, and upper one-third perineal body (PB) and the perineal mambrane. of the vagina. Both the uterosacral and cardinal ligaments are critical components of level I support and provide support for the According to DeLancey,6 the cervix and the upper one-third of the vaginal apex following hysterectomy6 (Fig. 2). The cardinal liga- vagina (level I) have relatively long suspensory fibers (uterosacral ments are oriented in a relatively vertical axis (in the standing and cardinal ligaments) that are vertically oriented in the standing posture) while the uterosacral ligaments are more dorsal in their position, while the mid portion of the vagina (level II) has a more orientation. direct attachment (pubocervical and rectovaginal fascia) laterally The suspensory ligaments hold the uterus in position over the to the pelvic wall. In the most caudal region (level III), the vagina is levator muscles that in turn reduce the tension on the ligaments attached directly to the structures that surround it (Fig. 1). At this and protect them from excessive tension.7 After a certain amount level, the levator ani muscles and the perineal membrane have of descent, the level I supports become taut and arrest further important supportive functions. cervical descent. Damage to the upper suspensory fibers allows In the upper part of the genital tract, a connective tissue uterine or apical segment to prolapse.8 complex attaches all the pelvic viscera to the pelvic sidewall. This endopelvic fascia forms a continuous sheet-like mesentery, Anterior compartment extending from the uterine artery at its cephalic margin to the point at which the vagina fuses with the levator ani muscles Anterior compartment support depends on the connections of below. The uterosacral and cardinal ligaments together support the vagina and periurethral tissues to the muscles and fascia of the the uterus and upper one-third of the vagina.6 At level II, the pelvic wall via the arcus tendineus fascia pelvis. On both sides of pubocervical and rectovaginal fascia form more direct lateral the pelvis, the arcus tendineus fascia pelvis is a band of connective attachments of the mid portion of the vagina to the pelvic walls. tissue attached at one end to the pubic bone and at the other end These lateral attachments stretch the vagina transversely between to the ischium, just above the spine. the bladder and the rectum.6 In the distal vagina (level III), the The anterior wall fascial attachments to the arcus tendineus vaginal wall is directly attached to surrounding structures. Ante- fascia pelvis is also defined as paravaginal fascial attachments. riorly, the vagina fuses with the urethra, posteriorly with the Anterior vaginal wall prolapse (cystocele) can occur either because perineal body, and laterally with the levator ani muscles.6 Damage of “lateral detachment” of the anterior vaginal wall at the pelvic to level I support can result in uterine or vaginal prolapse of the sidewall or as a “central failure” of the vaginal wall itself9 (Fig. 3). apical segment. Damage to the level II and III portions of vaginal However, if the cardinal and uterosacral ligaments fail, the upper support results in anterior and posterior vaginal wall prolapse.3,4 vaginal wall prolapses downward while the lower vagina (levels II The varying combinations of these defects are responsible for the and III) remains supported. diversity of clinically encountered problems and will be discussed in the following sections. Perineal membrane (urogenital diaphragm)

The “perineal membrane” is a dense connective tissue that Apical segment surround the urethra and close the anterior part of the pelvic outlet. It lies at the level of the hymen and attaches the urethra, In level I, the cardinal and uterosacral ligaments attach the vagina, and perineal body to the ischiopubic rami.10 The compres- cervix and the upper one-third of the vagina to the pelvic walls sor urethrae and urethrovaginal sphincter muscles are associated (Fig. 2). The uterosacral ligaments are bands of tissue running with the cranial surface of the perineal membrane. under the rectovaginal peritoneum composed of smooth muscle, loose and dense connective tissue, blood vessels, nerves, and Posterior compartment and anal sphincters lymphatics.6 They originate from the posterolateral aspect of the cervix at the level of the internal cervical os and from the lateral The posterior vagina is supported by connections between the vaginal fornix. The cardinal ligament is a mass of retroperitoneal vagina, the bony pelvis, and the levator ani muscles. The lower areolar connective tissue in which blood vessels predominate; it one-third of the vagina is fused with the perineal body (level III)

predominantly muscular and caudally fibroelastic. The fibroelastic tissue forms a network throughout the sphincter and passes through the subcutaneous EAS as bundles or fibers to insert into the perianal skin.12 The inferior outer aspect of the anal sphincter is formed by the cylindrical EAS which is a striated muscle under voluntary con- trol.12 The action of the EAS is voluntary closure and reflex closure of the anal canal and thereby contributes to the sphincter tone to some extent. The EAS has a thickness of 4 mm and it is approximately 2.7-cm high while it is shorter anteriorly in women, approximately 1.5 cm. Three different parts (deep, superficial, and subcutaneous) of the EAS can be identified at certain levels, which to some extent supports a multilayer anatomy.12 The “deep” part is intimately related to the PR muscle. The “superficial” part overlies the IAS at the middle level of the anal canal. Fibers of the anterior part of the EAS decussate into the transverse perineal muscle and perineal Fig. 3. Anterior vaginal wall prolapse may occur for the detachment of the body. Posterior fibers continues with the anococcygeal ligament. pubocervical fascia from the arcus tendineous fascia pelvis (lateral defect). The “subcutaneous” part extends approximately 1 cm beyond the IAS and envelops the lower part of the intersphincteric space. that connects the perineal membranes on either side. The mid- posterior vagina (level II) is connected to the inside of the levator ani muscles by sheets of endopelvic fascia. These connections Lateral compartment and the levator ani muscles prevent vaginal descent during increases in abdominal pressure. The fibers of the perineal membrane connect through the perineal Below and surrounding the pelvic organs is the levator ani body thereby providing a layer that resists downward descent of muscle. There are three major components of the levator ani the rectum.11 If this attachment becomes broken, then the resist- muscle13 (Fig. 5). The iliococcygeal portion forms a thin, relatively ance to downward descent is lost. flat, horizontal shelf that spans the potential gap from one pelvic The muscular structures that maintain fecal continence include sidewall to the other. The pubovisceral (also known as the the internal anal sphincter (IAS), the external anal sphincter (EAS), pubococcygeus) muscle attaches the pelvic organs to the pubic and the puborectalis (PR) muscle (Fig. 4). The anal canal is 2–4cm bone while the PR muscle forms a sling behind the rectum. The long. The spatial relationships between the internal and external lesser known subdivisions of the levator are pubovaginal, puboa- sphincters are such that the IAS extends above the EAS for a nal, and the puboperineal muscles.13 When these muscles and distance of greater than 1 cm.12 The internal sphincter lay con- their covering fascia are considered together, the combined struc- sistently between the external sphincter and the anal mucosa. It is tures are referred to as the pelvic diaphragm. a circular smooth muscle that is the continuation of the circular The opening between the levator ani muscles through which layer of the muscularis propria of the rectum. This layer increases the urethra, vagina, and rectum pass is the levator hiatus. The in thickness below the anorectal junction to form the IAS. The IAS portion of the levator hiatus ventral to the perineal body is has an important role in maintaining continence and is the main referred to as the urogenital hiatus, and it is through this that contributor to anal rest pressure. The IAS is approximately 2-mm prolapse of the vagina, uterus, urethra, and bladder occurs. The thick. The intersphincteric space is the plane between the sphinc- urogenital hiatus is bounded anteriorly by the pubic bones, ters containing loose areolar tissue. The longitudinal layer (con- laterally by levator ani muscles, and posteriorly by the perineal joined longitudinal layer or longitudinal muscle) is a sheet of body and external anal sphincter. The baseline tonic activity of the fibroelastic and muscular tissue. This layer is the continuation of levator ani muscle keeps the hiatus closed by compressing the the smooth muscle longitudinal layer of the rectum with contri- urethra, vagina, and rectum against the pubic bone, pulling the bution from the levator ani striated muscle (puboanalis) and pelvic floor and organs in a cephalic direction. This continuous fibroelastic components of the endopelvic fascia. Cranially it is muscle action closes the lumen of the vagina and forms a relatively

Fig. 4. The muscular structures of the anal canal include the internal anal sphincter, Fig. 5. Schematic view of the levator ani with its three major components: the the external anal sphincter, and the puborectalis muscle. iliococcygeous muscle, the pubococcygeous muscle, and the puborectalis muscle.

Downloaded for Roopa Ram ([email protected]) at University of Arkansas for Medical Services from ClinicalKey.com by Elsevier on February 05, 2019. For personal use only. No other uses without permission. Copyright ©2019. Elsevier Inc. All rights reserved. 8 G.A. Santoro, A.H. Sultan / Seminars in Colon and Rectal Surgery 27 (2016) 5–14 horizontal shelf on which the pelvic organs are supported. Damage inferior hemorrhoidal, which innervate the clitoris, the perineal to the levators resulting from nerve or connective tissue damage musculature, and inner perineal skin and the EAS, respectively. will leave the urogenital hiatus open and result in prolapse.14,15 Motor nerves to the IAS are derived from (1) L5 presacral plexus The interaction between the levator ani muscles and the sympathetic fibers, (2) S2–4 parasympathetic fibers of the pelvic endopelvic fascia is one of the most important biomechanical splanchnic nerve. features of pelvic organ support. As long as the muscles maintain their constant tone closing the pelvic floor, the ligaments of the endopelvic fascia have very little tension on them even with Pelvic floor imaging increase in abdominal pressure.6 If the muscles become damaged so that the pelvic floor sags downward, the organs are pushed The knowledge of pelvic floor anatomy and function is essential through the levator hiatus. Once they have fallen below the level of to effective imaging of pelvic floor defects. With advancing the hymenal ring, they are unsupported by the levator ani muscles technology, MRI and 3D ultrasound techniques have increased and the ligaments must carry the entire load. Although the our ability to detect pelvic floor defects and helped us gain insight endopelvic fascia can sustain these loads for short periods of time, into pathophysiology of pelvic floor disorders. An integrated if the pelvic muscles do not close the urogenital hiatus, the approach with a combination of different modalities has been connective tissue eventually fails, resulting in prolapse.16 The inter- described for a global and multicompartmental perspective of 5,18,19 actions between the pelvic floor muscles and endopelvic fascia are pelvic floor dysfunction. responsible for the pelvic organs support. It requires the dorsal traction of the uterosacral ligaments, and to some extent the cardinal Ultrasonographic techniques ligaments, to hold the cervix back in the hollow of the sacrum. It also requires the ventral pull of the pubovisceral portions of the levator Transperineal ultrasonography (TPUS) ani muscle to swing the levator plate more horizontally to close the TPUS is performed with the patient placed in the dorsal levator hiatus. It is, therefore, this interaction between the directions lithotomy position, with hips flexed and abducted, and a convex of these two forces that is so critical in maintaining the normal transducer positioned on the perineum between the mons pubis structural relationships that lessen the tension on ligaments and and the anal margin (perineal approach). Imaging is performed at muscles.16,17 rest, during maximal Valsalva maneuver, and during pelvic floor muscle contraction (PFMC). Conventional convex transducers (with frequencies of 3–6 MHz and field of view at least 701) Nerves provide 2D imaging of the pelvic floor.20,21 In the midsagittal plane, with an acquisition angle of 701 or more, all anatomical There are two main nerves that supply the pelvic floor relative structures (bladder, urethra, vaginal walls, anal canal, and rectum) to pelvic organ prolapse. One is the pudendal nerve that supplies between the posterior surface of the symphysis pubis and the the urethral and anal sphincters and perineal muscles, and the posterior part of the levator ani are visualized. A midsagittal view other is the nerve to the levator ani that innervates the major obtained will include the symphysis pubis, the urethra and musculature that supports the pelvic floor. These are distinct bladder, the vagina and uterus, the rectum, and the anal canal nerves with differing origins, courses, and insertions. The nerve (Fig. 6). Using 3D transabdominal probes developed for obstetric to the levator originates from S3 to S5 foramina, runs inside of the imaging (RAB 8-4, GE Healthcare Ultrasound, Milwaukee, WI; AVV pelvis on the cranial surface of the levator ani muscle, and 531, Hitachi Medical Systems, Tokyo, Japan; V 8-4, Philips Ultra- provides the innervation to all the subdivisions of the muscle. sound, Bothell, WA; 3D 4–7EK, Medison, Seoul, South Korea), 3D- The pudendal nerve originates from S2 to S4 foramina and runs and 4D-TPUS may be performed.22 These transducers combine an through Alcock's canal which is caudal to the levator ani muscles. electronic curved array of 4–8 MHz with mechanical sector tech- The pudendal nerve has three branches: the clitoral, perineal, and nology, allowing fast motorized sweeps through the field of view.

Fig. 6. 2D-transperineal ultrasound: midsagittal view showing symphysis pubis (SP), the urethra (U), bladder (B), the vagina (V), the rectum (R), the anal canal (AC), and the puborectalis muscle (PR). (A) Schematic drawing and (B) ultrasonographic view.

in anti-incontinence surgery, whose improper positioning or dislodgement may be associated with failed surgery26 (Fig. 8). Uterine prolapse is defined as downward displacement of the uterus beyond the halfway point of the vagina. Vaginal vault prolapse refers to descent of the vaginal apex in a patient who has had a hysterectomy and is commonly associated with enterocele or sigmoidocele. Continued descent of the apex of the vagina may result in complete eversion of the vagina. These conditions are usually obvious clinically, but dynamic 2D-TPUS can demonstrate the effect of the descending uterus on the bladder neck, urethra, or anorectum, explaining symptoms of voiding dysfunction or obstructed defecation. Posterior compartment prolapse includes rectocele, rectal intussusception, rectal prolapse, enterocele, and perineal descent. Symptoms that can be related to these disorders include obstructed defecation, such as incomplete evacuation, straining at stool, and vaginal digitation. Dynamic TPUS is able to demonstrate rectocele, enterocele, and rectal intussusception with images comparable to those of defecography.27–29 Rectocele is measured as the maximal depth of the protrusion beyond the expected Fig. 7. 2D-transperineal ultrasound. Bladder (B) base descent (cystocele) below the referral line (horizontal line to the inferior margin of the symphysis pubis—SP) margin of the normal anterior rectal wall. A herniation of a depth during maximal Valsalva maneuver (U: urethra). of over 10 mm has been considered diagnostic (Fig. 9). Rectal intussusception may be detected as an invagination of the rectal An advantage of this technique, compared with 2D mode, is the wall into the rectal lumen during maximal Valsalva maneuver. The opportunity to obtain tomographic or multislice imaging in order intussusception may also be observed to enter the anal canal or to assess the entire PR muscle and its attachment to the pubic rami exteriorized beyond the anal canal. Enterocele is diagnosed ultra- and to measure the diameter and area of the levator hiatus. sonographically as a herniation of bowel loops into the vagina. It Pelvic organ descent is usually assessed with 2D-TPUS.21–23 can be graded as small, when the most distal part descends into Anterior compartment prolapse, or “cystocele,” is common in the upper third of the vagina; moderate, when it descends into the women and may cause symptoms such as pelvic heaviness, the middle third of the vagina; or large, when it descends into the sensation of a lump, and voiding difficulty. Cystocele frequently lower third of the vagina. Enterocele may also coexist with coexists with other disorders involving the central and the rectocele.23 posterior compartments, such as uterine prolapse, rectocele, and Pelvic floor dyssynergy, also known as anismus, spastic pelvic enterocele. Dynamic 2D-TPUS demonstrates downward displace- floor syndrome, or paradoxical PR syndrome, is a phenomenon ment of the urethra and the presence of cystocele in the mid- characterized by a lack of normal relaxation of the PR muscle sagittal plane during maximal Valsalva maneuver24,25 (Fig. 7). during defecation. Dyssynergy is associated with symptoms of Ultrasonography also allows evaluation of mesh implants for obstructed defecation and incomplete emptying. Various TPUS anterior compartment prolapse.26 This is particularly useful con- abnormalities have been described during Valsalva maneuver: sidering that complications such as support failure, mesh erosion, the anorectal angle becomes narrower, the levator hiatus is and chronic pain are not uncommon. Sonographic imaging can shortened in the anteroposterior dimension, and the PR muscle determine the position, extent, and mobility of implants in the thickens as a result of contraction. This sonographic finding may anterior vaginal wall, dorsal to the trigone and posterior to the help to choose biofeedback therapy and to evaluate the results of bladder wall. Ultrasonography also allows evaluation of tapes used the treatment.

Fig. 8. 2D-transperineal ultrasound. Axial view of a transobturator tape (TOT) for stress urinary incontinence. (A) Normal positioning of the sling at midurethra level and (B) distal displacement of the sling causing recurrence of symptoms (B: bladder and U: urethra).

Fig. 10. 3D-endovaginal ultrasound. The levator ani (LA) is visualized as a multilayer hyperechoic sling coursing laterally to the vagina and posteriorly to the anal canal (AC) and attaching to the inferior pubic rami (IPR) anteriorly (OF: obturator foramen; SP: symphysis pubis; T: transducer; and U: urethra).

whereas tears may occur in any part of the muscle. Avulsion is a common consequence of overstretching of the levator ani during – Fig. 9. 2D-transperineal ultrasound: multicompartmental prolapse. Bladder base the second stage of labor and occurs in 10 36% of women at the descent (cystocele) below the referral line (horizontal line to the inferior margin of time of their first delivery. The functional and anatomical con- the symphysis pubis) during maximal Valsalva maneuver. Rectocele is visualized as sequences of levator ani avulsion are considerable, with a reduc- the protrusion of the anterior rectal wall beyond the expected margin. tion in muscle strength of about one-third and marked alteration of anatomy. The main effect of avulsion is due to enlargement of Endovaginal ultrasonography (EVUS) the levator hiatus that may result in excessive loading and failure EVUS is performed with a high multifrequency (9–16 MHz), of ligamentous and fascial structures, which may, over time, lead 3601 rotational mechanical probe (type 2052, B-K Medical, Herlev, to the development of prolapse.33 Denmark) or with a radial electronic probe (type AR 54 AW, 5– 10 MHz, Hitachi Medical Systems).5 The 3D acquisition is free- Endoanal ultrasonography (EAUS) hand with the electronic transducer, whereas the mechanical 3D-EAUS is firmly established as one of the cornerstones of a transducer has an internal automated motorized system that colorectal diagnostic work-up, and it is performed with the same allows an acquisition of 300 aligned transaxial 2D images over a probes adopted for 3D-EVUS.34,35 During examination, the patient distance of 60 mm in 60 s, without any movement of the probe may be placed in a dorsal lithotomy, left lateral, or prone position. within the tissue.30 The set of 2D images is reconstructed instanta- However, irrespective of patient position, the transducer should neously into a high-resolution 3D image for real-time manipula- be rotated so that the anterior aspect of the anal canal is superior tion and volume rendering. An advantage of 3D compared with 2D mode is the opportunity to obtain sagittal, axial, coronal, and any desired oblique sectional image. The 3D image may be rotated, tilted, and sliced to allow the operator to vary infinitely the different section parameters, to visualize and measure distance, area, angle, and volume in any plane. The 3D volume can also be archived for offline analysis on the ultrasonographic system or on a PC with the help of dedicated software. 3D-EVUS provides a topographical overview of pelvic floor anatomy. Four levels of assessment in the axial plane can be defined.30 At the highest level (level I), the bladder base can be seen anteriorly and the inferior third of the rectum posteriorly. Level II corresponds to the bladder neck, the intramural region of the urethra, and the anorectal junction. Level III corresponds to the midurethra and the upper third of the anal canal. At this level, the levator ani can be visualized as a multilayer hyperechoic sling coursing laterally to the vagina and posteriorly to the anal canal and attaching to the inferior pubic rami anteriorly. Levator hiatus dimensions (anteroposterior and laterolateral diameters and area) can be measured31 (Fig. 10). At the lowest level (level IV), the superficial perineal muscles (bulbospongiosus, ischiocavernosus, and superficial transverse perineal muscles), the perineal body, the distal urethra, and the middle and inferior thirds of the anal canal can be visualized.11 3D-EVUS may be utilized to document major levator trauma 32 Fig. 11. 3D-endovaginal ultrasound. The levator ani (LA) is disconnected (avulsion) (Fig. 11). Levator avulsion is the disconnection of the muscle from from the left inferior pubic rami (IPR) (arrows) (A: anal canal; SP: symphysis pubis; its insertion on the inferior pubic ramus and the pelvic sidewall, and U: urethra).

Fig. 12. 3D-endoanal ultrasound. The anal canal is divided into three levels of assessment in the axial plane, deﬁned by the following landmarks: (A) upper level: puborectalis muscle (PR); (B) middle level: internal (IAS) and external anal sphincter (EAS); (C) lower level: external anal sphincter.

(12 o'clock position) on the screen, the right lateral aspect is to the to evaluate posterior compartment prolapse.40 The patient is left (9 o'clock), the left lateral aspect is to the right (3 o'clock), and the examined in the left lateral position. Images are acquired by four posterior aspect is inferior (6 o'clock). The recording of data should automatic scans: Scan 1 (at rest position without gel): the trans- extend from the upper aspect of the PR muscle to the anal verge. ducer is positioned at 5.0–6.0 cm from the anal margin. It is With EAUS, the anal canal is divided into three levels of assess- performed to visualize the anatomic integrity of the anal sphincter ment in the axial plane35 (Fig. 12): (1) the upper level corresponds musculature and to evaluate the position of the PR and EAS at rest; to the hyperechoic sling of the PR muscle and the concentric Scan 2 (at rest—straining—at rest without gel): the transducer is hypoechoic ring of the IAS. In males, the deep part of the EAS is positioned at 6.0 cm from the anal verge. The patient is requested also identified at this level; (2) in the middle level, the complete to rest during the first 15 s, strain maximally for 20 s, then relax ring of the superficial EAS (concentric band of mixed echogenicity), again, with the transducer following the movement. The purpose the conjoined longitudinal layer, the complete ring of the IAS, and of the scan is to evaluate the movement of the PR and EAS during the transverse perinei muscles are visualized; and (3) the lower straining, identifying normal relaxation, nonrelaxation, or para- level corresponds to the subcutaneous part of the EAS. doxical contraction (anismus); Scan 3: the transducer is positioned EAUS has been recommended by the International Consultation proximally to the PR (anorectal junction). The scan starts with the on Incontinence as the gold standard investigation to identify anal patient at rest (3.0 s), followed by maximum straining with the sphincter injury in fecal incontinence (FI).36 It can differentiate transducer in fixed position (the transducer does not follow the between incontinent patients with intact anal sphincters and descending muscles of the pelvic floor). When the PR becomes those with sphincter lesions (defects, scarring, thinning, thicken- visible distally, the scan is stopped. Perineal descent is quantified ing, and atrophy).37,38 Tears are identified by interruption of the by measuring the distance between the position of the proximal circumferential fibrillar echo texture (Fig. 13). Scarring is charac- border of the PR at rest and the point to which it has been terized by loss of normal architecture, with an area of amorphous displaced by maximum straining (PR descent). Straining time is texture that usually has low reflectivity. Ultrasonography also directly proportional to the distance of perineal descent; Scan 4: allows evaluation of anti-incontinence surgery (sphincter repair, following injection of 120–180 ml ultrasound gel into the rectal graciloplasty, bulking agents injection).39 ampulla, the transducer is positioned at 7.0 cm from the anal verge. The scanning sequence is the same as in Scan 2 (at rest— 15 s, strain maximally—20 s, then relax again with the transducer Echodefecography (EDF) following the movement). The purpose of the scan is to visualize This is a 3D dynamic anorectal ultrasonographic modality and quantify all anatomical structures and functional changes performed with the same 3601 rotating transducer used for EAUS associated with voiding (rectocele, intussusception, grade II or III sigmoidocele/enterocele). In normal patients, the posterior vaginal wall displaces the lower rectum and upper anal canal inferiorly and posteriorly but maintains a straight horizontal position during defecatory effort. If rectocele is identified, it is classified as grade I (o6.0 mm), grade II (6.0–13.0 mm), or grade III (413.0 mm) (Fig. 14). Intussusception is clearly identified by observing the rectal wall layers protruding through the rectal lumen. Grade II or III sigmoidocele/enterocele is recognized when the bowel is positioned below the pubococcygeal line (on the projection of the lower rectum and upper anal canal).41,42

Magnetic resonance imaging (MRI)

Static MRI Static MRI provides detailed information on pelvic floor anatomy. Current state-of-the-art MR of the pelvic floor includes Fig. 13. 3D-endoanal ultrasound. Internal (IAS) and external anal sphincter (EAS) fi lesions in the anterior quadrant of the middle level of the anal canal. The muscle is imaging at a magnetic eld strength of 1.5 Tesla (T), using pelvic replaced by a mixed echogenicity scar tissue (ST). or phased array coils and T2-weighted fast spin-echo (FSE)

Fig. 15. Pelvic MRI with external phased array. The levator ani (LA) is damaged on the right side (arrow), with a complete detachment from the inferior pubic rami (AC: anal canal; SP: symphysis pubis; U: urethra; and V: vagina). Fig. 14. 3D-echodefecography. Rectocele is identified for the displacement of the anterior wall of the lower rectum (arrows) and the protrusion of the posterior the inferior border of the symphysis pubis to the last or second last vaginal wall (EAS: external anal sphincter and PR: puborectalis muscle). coccygeal joint.45 The anorectal junction (ARJ) is defined as the cross point between a line along the posterior wall of the distal sequences.43 The spatial resolution can be enhanced by using part of the rectum and a line along the central axis of the anal endoluminal (endorectal, endovaginal) coils. In combination with canal. To determine pathologic pelvic floor descent, the measure- T2-weighted FSE sequences, endoluminal coils provide improved ments are made on the images, which show maximal organ signal-to-noise ratio (SNR) and high-resolution images. Based on descent, usually during maximal straining or during evacuation. T2-weighted turbo spin-echo sequences, muscles are relatively The anorectal angle (ARA) is defined as the angle between the hypointense, ligaments and fascia hypointense, while fat and posterior wall of the distal part of the rectum and the central axis smooth muscle are hyperintense. The prominent pelvic floor of the anal canal and can be measured at rest, squeezing, and structures of the posterior compartment visualized at MRI are straining. Dynamic MRI may be used to demonstrate posterior (1) perineal body and superficial perineal muscles; (2) anal compartment prolapse during maximal Valsalva maneuver: sphincters: the IAS is easily recognized as a circular hyperintense structure. It is approximately 2.9 mm thick on endoluminal MRI. Rectocele: measured as the depth of wall protrusion beyond the The intersphincteric space is seen as a bright line on T2-weighted expected margin of the normal anorectal wall. Based on sagittal MRI. The EAS has a thickness of 4.1 mm on endoluminal imaging; MR-sections through mid of pelvis, rectoceles are graded as (3) PR muscle and levator ani; and (4) rectum and rectal support. small (o2 cm), moderate (from 2 to 4 cm), and large (44 cm) Endoanal MRI has been demonstrated to be comparable to (Fig. 17); EAUS in the detection of anal sphincter defects in FI.44 External Rectal intussusception: the infolding of the rectal mucosa phased array coil MRI can replace endoluminal MRI with com- occurring during defecation. Depending on the location, an parable results.44 Abnormalities of the levator ani are identified on MRI as present or absent. Defect severity is further scored in each muscle from 0 (no defect) to 3 (complete loss) (Fig. 15). A summed score for the two sides (0–6) is assigned and grouped as minor (0– 3) or major (4–6).

Dynamic MRI With the development of fast multislice sequences, MR imaging has gained increasing acceptance for dynamic imaging of pelvic floor. Because the posterior compartment is traditionally in the focus of interest, dynamic MR imaging of the pelvic floor is often called “MR defecography.”45 Dynamic pelvic imaging may be performed in an open-configuration MR system in the sitting position, or in a closed-configuration MR-system in the supine position. Both techniques are equally effective in identifying most of the clinically relevant abnormalities of the pelvic floor. For evaluation of the posterior compartment, the rectum should be filled with a contrast agent (ultrasound gel or mashed potatoes, gadolinium-based MR contrast agent) to study the actual act of defecation. The use of reference lines for image evaluation is helpful Fig. 16. Dynamic MRI of the pelvic floor. Multicompartmental prolapse. Bladder (Fig. 16). The most used reference line is the pubococcygeal line (B) base, uterus (U), and rectum (R) descent below the pubococcygeal line (PCL) (PCL), which is defined on midsagittal images as the line joining during maximal Valsalva maneuver.

proceeding promptly and to completion, and (5) lack of significant pelvic floor descent. After evacuation is complete, the anal canal should close, the ARA recover, and the pelvic floor return to its normal baseline position. Post toilet imaging may be required, particularly in those suspected of retained barium within rectoceles. The major function of proctography is not merely to document evacuatory abnormalities,49,50 but also to classify those abnormalities into those potentially surgically relevant, those likely to benefit from behavioral biofeedback therapy alone, or indeed those which are incidental:

Pelvic floor descent: it is defined as the distance moved by the ARJ or ARA at rest to the point of anal canal opening and is considered abnormal if it exceeds 3 cm; Intussusception and prolapse: refers to infolding of the rectal wall into the rectal lumen. It may be described as intrarectal, intra-anal, or external to form a complete rectal prolapse; Rectocele: it is defined as any anterior rectal bulge. The depth of Fig. 17. Evacuation proctography. Rectocele is visualized as a bulging of the anterior a rectocele is measured from the anterior border of the anal rectal wall. canal to the anterior border of the rectocele (Fig. 17). A distance of o2 cm is classified as small, 2–4 cm as moderate, and intrarectal intussusception, limited to the rectum, is distin- 44 cm as large. Of more relevance, however, is barium trap- guished from an intra-anal intussusception extending into the ping at the end of evacuation; anal canal. The location of the intussusception may be anterior, Enterocele: it is diagnosed when small bowel loops enter the posterior, or circumferential. The intussusception either peritoneal space between the rectum and vagina. Diagnosis of involves only the mucosa or the full thickness of the rectal an enterocele on proctography is only really possible if oral wall46; contrast has been administered before the examination. Her- Enterocele: defined as a herniation of the peritoneal sac, which niation of the sigmoid into the rectogenital space (sigmoido- contains omental fat (peritoneocele), small bowel (enterocele), cele) is significantly less common than an enterocele; and or sigmoid (sigmoidocele), into the rectovaginal or rectovesical Dyssynergic defecation: various proctographic abnormalities space below the PCL. The largest distance between the PCL and have been described including prominent PR impression, a the most inferior point of the enterocele is measured with a narrow anal canal, and acute ARA. However, these observations perpendicular line. Depending on this distance, small (o3 cm), may be found in normal controls and are in themselves moderate (3–6 cm), and large (46 cm) enteroceles are unreliable distinguishing features. distinguished47; Dyssynergic defecation: different structural imaging findings Conclusion can be seen on dynamic pelvic MRI, including prominent impression of the PR sling, narrow anal canal, prolonged Care of women with pelvic floor disorders begins with an evacuation, a lack of descent of the pelvic floor, and thus a understanding of the unique musculofascial system that supports failure to increase the ARA. the pelvic organs. The principles underlying reconstructive surgery are either restoration of normal anatomy and thereby a presumed Evacuation proctography return to normal function, or creation of compensatory anatomical mechanisms. Combining different imaging modalities has the This modality evaluates in real time the morphology of rectum potential to complement the advantages and to overcome the and anal canal in correlation with pelvic bony components both limitations of each of these tools and to substantially improve the statically and dynamically by injection of a thick barium paste into clinical management of these conditions.51 the rectum and its subsequent evacuation. Contrast administration into the bladder and vagina provides a more comprehensive “ assessment of the pelvic organs and has been labeled dynamic References cystoproctography.” At rest, the anal canal is closed and rectum fi assumes its normal upright con guration. The position of the 1. DeLancey JO. 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