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State of the Art |
1 From the Department of Radiology, Academic Medical Center, University of Amsterdam, PO Box 22700, 1100 Amsterdam, the Netherlands (J.S.), and the Intestinal Imaging Centre, St Mark’s Hospital, London, England (S.H., C.I.B.). Received June 18, 1999; revision requested August 9; revision received November 9; accepted November 16; updated September 28, 2000. Address correspondence to J.S. (e-mail: j.stoker@amc.uva.nl).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONANATOMYPHYSIOLOGY FUNCTIONAL DIAGNOSTIC TESTS IMAGING TECHNIQUES PATHOLOGIC CONDITIONS CONCLUSIONREFERENCES |
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Index terms: Bladder, abnormalities, 83.832, 83.835 • Colon, abnormalities, 75.133, 75.15, 75.27, 75.73, 75.79, 75.791 • Colon, MR, 75.121411, 75.121412 • Colon, US, 75.12981, 75.12989 • Pelvic organs, 80.11 • Pelvic organs, MR, 80.121411, 80.121412 • Pelvic organs, US, 80.12981, 80.12989 • State of the Art • Urine, incontinence, 82.835
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONANATOMYPHYSIOLOGY FUNCTIONAL DIAGNOSTIC TESTS IMAGING TECHNIQUES PATHOLOGIC CONDITIONS CONCLUSIONREFERENCES |
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ANATOMY |
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TOPABSTRACTINTRODUCTIONANATOMYPHYSIOLOGY FUNCTIONAL DIAGNOSTIC TESTS IMAGING TECHNIQUES PATHOLOGIC CONDITIONS CONCLUSIONREFERENCES |
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Pelvic Floor
The pelvic floor is a complex, integrated, multilayer system that provides active and passive support. Fascia and ligaments provide passive support, while the muscles of the pelvic floor, mainly the levator ani, provide active support. The fascia is attached to the bone ring of the pelvis, with the ligaments formed from fascial condensations. The pelvic floor has three layers from superior to inferior: the pelvic fascia, pelvic diaphragm, and urogenital diaphragm, with their associated supportive structures, which are intimately related to the urogenital region, urethra, anal sphincter, and vagina in women.
Pelvic Fascia
Pelvic fasciae are delicate structures, most of which are below imaging resolution. The most cephalad layer covers the levator ani muscle and viscera in a continuous sheet. At the uterine level, this layer is called the parametrium; at the vaginal level, it is called the paracolpium (4). Two dense aggregations of obturator and levator ani fasciae, the arcus tendineus fasciae pelvis and arcus tendineus levator ani, provide important passive lateral support (Figs 1, 2). The arcus tendineus fasciae pelvis provides lateral anchoring for the anterior vaginal wall where it underlies and supports the urethra, while the arcus tendineus levator ani provides anchoring for the levator ani muscles. The arcus tendineus levator ani can be identified on magnetic resonance (MR) images as the origin of a part the levator ani muscle (iliococcygeus muscle) at the internal obturator fascia (Figs 2–4) (4). The arcus tendineus fasciae pelvis (Figs 1, 2), although visualized at high-spatial-resolution MR imaging in a cadaver (5), is difficult to identify with certainty in vivo. This is due to the difficulty in differentiating this fascial aggregation from other closely aligned fascial structures and vessels.
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Pelvic Diaphragm
The levator ani is the major muscle of the pelvic diaphragm; it is attached to the pubis and supportive fascia by the arcus tendineus levator ani (Figs 3–5). The levator ani is readily visible at MR imaging. Several segments of the levator ani have been described in terms of their visceral insertions, although these are inseparable parts of a single unit (5). The ventromedial part of the levator ani, variously called the pubococcygeus muscle, pubovisceralis muscle, or puborectal muscle, is a thick, slinglike bundle of fibers arising from the inner aspect of the pubis, passing beside the urethra, vagina (Figs 3, 6), and anorectum (Figs 5, 7), and attaching to the vagina and anorectum (5). The slinglike configuration of the ventromedial part of the puborectal muscle may give the false impression that it is a separate muscle. Tonic contraction of the two parts of this sling closes the urogenital and anorectal hiatus, which provides a supportive platform during normal activity and standing. Constant tone is maintained by means of slow-twitch (type I) muscle fibers (7). The iliococcygeus and coccygeus muscles also are part of the levator ani. The origin of the iliococcygeus muscle is the arcus tendineus levator ani (Figs 2–4). The levator ani is innervated by sacral nerve roots S2 through S4 via the pudendal nerve.
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Urethra
The female urethra is approximately 4.5 cm long, with two-thirds of the urethra above the levator ani (pelvic diaphragm). The proximal one-third of the female urethra and the proximal (prostatic) male urethra are lined with transitional cell epithelium. The more distal portion of the urethra is lined with (pseudo-) stratified columnar epithelium. Infoldings of urothelial tissue with rich submucosal vascular plexuses, mucosal secretions, and urethral smooth muscle all contribute to passive urethral closure (urethral coaptation, mucosal seal) (9,10).
The urethral sphincter is composed of involuntary inner smooth muscle that is continuous with the bladder, as well as the voluntary external sphincter (rhabdosphincter), which is composed of striated muscle. Mucosa and submucosa, inner smooth muscle, and external urethral striated sphincter are readily visible at high-resolution MR imaging in all individuals (Figs 6, 7). The inner smooth muscle sphincter extends throughout the proximal two-thirds of the urethra, and its tension is distributed relatively uniformly and contributes to about one-third of intraurethral pressure (10). The smooth muscle of the urethra has high signal intensity on T2-weighted MR images and demonstrates enhancement after intravenous administration of contrast medium (8). This manifestation is common to smooth muscle sphincters, including the smooth muscle internal anal sphincter. Although this manifestation probably is related to the specific histologic characteristics of smooth muscles, no definite explanation is available, to our knowledge.
The external sphincter contributes mainly to resting pressure by means of slow-twitch muscle fibers. The urogenital diaphragm muscle (deep transverse muscle of the perineum) predominantly contributes to voluntary and reflex muscle contraction. There is debate with regard to the neural pathways to the external urethral sphincter (11).
Urethral and Bladder Neck Supporting Structures
Fascial and ligamentous support of the urethra and the bladder neck is vital to preserve urinary continence. Recent research with cadaver dissection in combination with MR imaging has provided insights into the anatomy of urethral and bladder neck support. However, the exact anatomy remains to be established, and the terminology used is confusing. A description of the most important structures will be provided in this article, but for a detailed description the reader is referred to other sources (4,8,12–15).
Vesicopelvic, urethropelvic, and pubourethral ligaments and fascia give anterior and lateral support to the bladder neck and urethra by means of attachment to the pubic bone and arcus tendineus fasciae pelvis (Fig 2) (12,13). Current research with high-resolution MR imaging in cadavers and in vivo is directed to revealing which ligaments and muscles can be identified. The urethropelvic ligaments can be easily identified with high-resolution MR imaging in almost all individuals, but there is no consensus about whether these structures insert directly into the levator ani muscle or through another (periurethral) ligament (Figs 6, 7) (8,13). Other ligaments between the urethra and pubic arch (pubourethral ligament) and between the bladder and pubic arch (vesicopelvic ligament) can be identified in some individuals. The pubovesical ligament or muscle (Fig 2), an extension of detrusor smooth muscle coursing through the retropubic space to the arcus tendineus fasciae pelvis, has been identified at high-resolution MR imaging in a cadaver (5) and may assist in opening the bladder neck during voiding. Bladder neck position is influenced by connections between the puborectal muscle, vagina, and proximal urethra (16).
Urogenital Region
The urogenital region forms the superficial part of the anterior pelvic floor. The external genital muscles—the superficial transverse muscle of the perineum, the bulbocavernous (bulbospongiosus) muscle, and the ischiocavernous muscle—lie within this region, as does the urethrovaginal sphincter in women (Fig 8). The urethrogenital sphincter encircles the urethra and vagina. This sphincter has been considered part of the deep transverse muscle of the perineum (urogenital diaphragm), but the authors of a recent endovaginal MR imaging study (8) suggested that it might be part of the puborectal (pubococcygeus) muscle. In women, the bulbocavernous muscles inserts into the pubic arch and the root and dorsum of the clitoris and has attachments to the vagina and urogenital diaphragm (8). The external genital muscles are visible with high-resolution MR imaging in all individuals (Fig 8).
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Perineal Body
Directly anterior to the anal sphincter is the perineal body (central tendon of the perineum). In men, it is posterior to the spongious and cavernous bodies and their related muscles, whereas in women it lies within the anovaginal septum (Fig 9). Many structures insert fibers into the perineal body, including the external anal sphincter, the deep and superficial transverse muscles of the perineum (urogenital diaphragm), and the bulbocavernous and puborectalis (pubococcygeus) muscles. The superficial transverse muscle of the perineum spans the dorsal edge of the urogenital diaphragm and elevates the perineal body.
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The internal sphincter forms the innermost muscular layer and is the terminal condensation of the circular rectal smooth muscle (Fig 5). The internal sphincter extends from the anorectal junction to approximately 1–1
cm below the dentate line. It is composed of smooth muscle fibers with autonomous innervation from sympathetic presacral nerves. The longitudinal muscle (Fig 5) is the continuation of the longitudinal muscle of the rectal wall. There is a large fibroelastic element derived from the pelvic fascia that invests both sphincters. The longitudinal muscle is closely related to the subcutaneous external sphincter. Some authors have stated that the longitudinal muscle ends in the subcutaneous external sphincter, while others have stated that this muscle passes through the subcutaneous external sphincter to terminate in the perianal skin (20).
The external sphincter is the outermost muscle of the distal anal canal (Figs 5, 8, 10) and is composed of several parallel bundles (20). It is a circular structure and is shorter anteriorly in women, approximately 1 cm. The external sphincter extends approximately 1 cm beyond the internal sphincter (Fig 5). The deep part of the external sphincter is fused with or intimately related to the puborectalis muscle. Anteriorly, it is closely related to the superficial transverse muscle of the perineum and the perineal body (Figs 8, 9). Posteriorly, the muscle is continuous with the anococcygeal ligament (Figs 8–10). All sphincter muscles are readily seen at endoanal MR imaging. The muscle is under voluntary control and is innervated by the pudendal nerves (S2 through S4). The puborectalis muscle has separate innervation from S3 and S4.
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PHYSIOLOGY |
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TOPABSTRACTINTRODUCTIONANATOMYPHYSIOLOGY FUNCTIONAL DIAGNOSTIC TESTS IMAGING TECHNIQUES PATHOLOGIC CONDITIONS CONCLUSIONREFERENCES |
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Micturition
The bladder can accommodate large volumes without substantially increased intravesicular pressure because of the passive viscoelastic properties of the smooth muscle and connective tissue of its wall. Filling leads to reflex stimulation of 
-adrenergic receptors within the bladder neck and proximal urethral smooth muscle, which increases outlet resistance. The efferent somatic nerves also stimulate the striated muscular external urethral sphincter. During bladder contraction, there is coordinated opening first of the proximal sphincter, with funneling of the vesical neck and proximal urethra and then of the distal sphincter, at which time voiding will ensue. If the sphincter contracts during bladder contraction, continence will be maintained or voiding will cease if the pressure is greater than that within the urethra or bladder.
Anal Continence
Anal continence is maintained by means of a complex interrelationship between anal and pelvic floor musculature integrated by means of somatic and autonomic nervous control. The smooth muscle of the internal sphincter maintains a tonic contraction, keeping the anal canal closed at rest. The puborectalis muscle and external anal sphincter also display some resting tone but contract rapidly to prevent incontinence in response to any sudden increase in intraabdominal pressure.
Defecation
It is likely that defecation is initiated by colonic smooth muscle contractions, which are provoked by waking and after eating. These contractions propel stool from the sigmoid colon into the normally empty rectum and stimulate rectal sensory nerves that produce an urge to defecate. These nerves are also used to determine the nature of rectal content. The sensation of a full rectum and the ability to discriminate gaseous, liquid, and solid content are important components of continence. Interestingly, sensation is retained after rectal excision, suggesting that some sensory receptors reside in the pelvic floor (25). Rectal filling causes reflexive internal sphincter relaxation (the rectoanal inhibitory reflex), rectal contraction, and contraction of the puborectalis muscle and external sphincter, both of which are heavily modulated with conscious control. Stool in the anal canal contacts sensory receptors concentrated at the level of the dentate line and greatly intensifies the urge to defecate, which is resisted by vigorous striated muscle contraction until circumstances for defecation are appropriate. When such circumstances are present, pelvic floor relaxation and increased intraabdominal pressure create a positive pressure gradient from the rectum to the anus to allow evacuation.
Internal sphincter disorders result in passive incontinence (ie, fecal leakage without awareness) (26), whereas external sphincter damage results in urge incontinence (ie, the patient is unable to delay defecation).
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FUNCTIONAL DIAGNOSTIC TESTS |
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TOPABSTRACTINTRODUCTIONANATOMYPHYSIOLOGY FUNCTIONAL DIAGNOSTIC TESTS IMAGING TECHNIQUES PATHOLOGIC CONDITIONS CONCLUSIONREFERENCES |
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Flow rate measurement is an index of the volume voided in a unit time, expressed as millimeters per second. Detrusor underactivity, instability, and outlet obstruction produce abnormal flow patterns. Cystometrography (CMG) is used to measure the relationship between bladder pressure and volume for evaluation of the detrusor functions of compliance and contractility. Urethral pressure profiles are records of intraurethral pressure and can demonstrate pressure equalization between the bladder and urethra at the high-pressure area, which, in the absence of detrusor activity, is considered to be indicative of genuine stress incontinence (ie, urinary incontinence caused by hypermobility of the bladder neck) (29). Detrusor leak-point pressure and abdominal leak-point pressure represent those bladder pressures at which leakage occurs in the absence of increased intraabdominal pressure and at straining, respectively (9). An abnormality suggests an intrinsic sphincter deficiency, and the examination should be performed in conjunction with fluoroscopy to identify potential pitfalls such as the presence of a cystocele (9).
Video urodynamics (VUDO), also called video cystourethrography, is considered to be the best method for investigation of lower urinary function but remains relatively underevaluated (29,30). It is a combination of CMG and voiding cystourethrography that integrates pressure and imaging studies (9). Common indications include failed incontinence surgery and equivocal results after urodynamics. VUDO is a routine technique in many tertiary referral centers. An intravesicular catheter is used to measure bladder pressure during filling with contrast medium, as in CMG, to provide information on bladder capacity and compliance. Simultaneous measurement of intraabdominal pressure is achieved by means of a rectal or vaginal catheter, and subtraction of intraabdominal pressure from intravesicular pressure determines the true detrusor pressure. Urethral closure pressure can be calculated from the difference between urethral and bladder pressures. Voiding flow rate and voided volume are measured by using a transducer placed under a collecting receptacle. Interruption of voiding allows observation of bladder neck closure and urethral "milk-back." Urodynamic measurements are integrated with fluoroscopic findings.
Anorectal Physiology Testing
A variety of techniques are available to test anorectal nerve integrity, conduction, and muscular performance. Few are absolutely diagnostic, and most must be considered together with symptoms, clinical findings, and imaging results. However, these techniques provide valuable complementary information that radiologists working in this field should be aware of. Normal values vary between laboratories.
Manometry
Manometry is used to determine rectal and anal pressures. The systems in use vary in complexity from simple balloons connected to a pressure transducer to perfused multichannel catheters capable of simultaneous measurement of pressures at several sites to ambulatory systems that can record for 24 hours or longer. The pressure recorded will increase when a rectal catheter is withdrawn into the anus and decrease again when it reaches the anal margin, indicating the functional anal canal length. This is usually longer than its anatomic length. A static anal catheter will measure resting anal canal pressure, which is predominantly an internal sphincter function (31).
Resting pressure is reduced in incontinence, owing to abnormality of the internal sphincter. In contrast, squeeze pressure, the incremental increase over resting pressure elicited when the patient is asked to voluntarily contract his or her anus, reflects external sphincter function. This may be reduced when incontinence is due to external sphincter tears, such as those that occur with obstetric injury. A dual sphincter abnormality is suggested when both resting and squeeze pressures are abnormal.
Pudendal Nerve Latency
Pudendal nerve terminal motor latency can be determined on the basis of the time needed for a digitally delivered pudendal nerve stimulus to elicit anal contraction. This is measured by using a disposable glove with a stimulating electrode at the fingertip coupled with a pressure sensor at the base of the glove. The nerve is stimulated near the ischial spine and has both sensory and motor components. Slow conduction is thought to be due predominantly to a stretch-induced injury. This may follow childbirth (32) or chronic straining and is a transient phenomenon even in healthy subjects asked to strain excessively. The clinical relevance of pudendal neuropathy remains unclear, not least because it is a normal feature of aging. The degree of neuropathy and pelvic floor descent should be directly related, although this has not been demonstrated (33). Incontinence is usually attributed to neuropathic sphincter degeneration if the latencies are abnormal and the sphincters intact. Sphincter repair is less successful if there is an underlying neuropathy (34).
EMG Studies
A needle electrode inserted into the external sphincter can determine both its electric activity and quality. Denervation is followed by reinnervation via neighboring healthy axons and is identified at EMG when the recorded action potentials become polyphasic. Prior to endoanal ultrasonography (US), EMG was the only reliable method to preoperatively identify external sphincter tears. No muscle potential would be seen in an area of scarring. Circumferential needle passes around the anus would "map" the extent of the muscle tear or "defect." EMG is painful, and a local anesthetic cannot be used because it interferes with recording. Fortunately, endoanal US is superior for detecting sphincter defects (35).
EMG may be combined with defecography to record external sphincter activity during evacuation. Normally, striated muscle should switch off completely during evacuation. Increased activity suggests anismus. Anismus can be defined as functional evacuatory failure, frequently associated with involuntary contraction, instead of relaxation, of striated pelvic floor musculature during attempted evacuation. Anismus may also be diagnosed manometrically if anal canal pressure increases paradoxically during straining.
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IMAGING TECHNIQUES |
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TOPABSTRACTINTRODUCTIONANATOMYPHYSIOLOGY FUNCTIONAL DIAGNOSTIC TESTS IMAGING TECHNIQUES PATHOLOGIC CONDITIONS CONCLUSIONREFERENCES |
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A low resting position for the bladder neck and basal descent of 1 cm or more are used to identify hypermobility of the bladder neck in stress incontinence, although there is some overlap with findings in healthy subjects (38,39,41). Rotational descent of the proximal urethra is common in stress urinary incontinence (42). The volume of the striated muscular sphincter (rhabdosphincter), determined with three-dimensional transperineal US, is decreased in genuine stress incontinence (43).
Voiding Cystourethrography
Voiding cystourethrography (VCUG) is performed primarily to detect a cystocele and evaluate urethrovesical junction mobility. When combined with evacuation proctography, VCUG is termed cystoproctography (44–47). Lateral fluoroscopy at rest, during coughing, and during voiding helps differentiate between bladder neck descent or urethrovesical junction hypermobility, defined by bladder base descent below the inferior margin of the pubic symphysis (45), and bladder base descent (cystocele) (Fig 11) (46). A cystocele is frequently overlooked during physical examination, and VCUG or cystoproctography are more accurate. Urethrovesical junction mobility can be related to bone landmarks (pubococcygeal line) or a small radiopaque intraurethral tube (45), with travel of more than 1 cm indicative of hypermobility (46). An open bladder neck and proximal urethra at rest in the absence of detrusor contraction (funneling) may indicate an intrinsic sphincter deficiency (urethral sphincter defect). However, there is a weak relationship between bladder neck funneling at rest and urodynamic parameters of intrinsic sphincter deficiency (46,47).
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Endoanal US
Endoanal US of the anal sphincters is achieved by the simple expedient of replacing the balloon system used for rectal scanning with a hard cone (57). The cylindric nature of the anal structures favors the 360° axial view at right angles to the lumen obtained with a mechanically rotated endoprobe. The cone is filled with degassed water for acoustic coupling and is covered with a lubricated condom. It is introduced into the rectum, aligned in standard orientation with the anterior end uppermost, and then slowly withdrawn down the anal canal. Images are obtained at proximal, middle, and distal levels. Some image asymmetry may be induced if the patient is in a left-lateral position, and it is preferable to examine the patient prone.
The puborectalis muscle and transverse perinea demarcate the proximal portion of the canal. The former blends into the external sphincter in the middle part of the canal, forming a complete ring anteriorly. The internal sphincter is thickest in the middle part of the anal canal and is of uniformly low reflectivity, contrasting sharply against the more heterogeneous subepithelial tissues medially and the longitudinal muscle laterally (Fig 12). The subcutaneous external sphincter, lying below the termination of the internal sphincter, defines the distal portion of the canal. Although the external sphincter, intersphincteric plane, and longitudinal muscle are each relatively heterogeneous, there are characteristic features visible when the latest generation of high-frequency (10-MHz) transducers, which allow these to be distinguished, are used.
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MR Imaging of the Anal Sphincter
The anal sphincter can be visualized with the body coil alone or with a phased-array or endoluminal coil. Examination with an endoluminal coil results higher spatial resolution but a limited field of view (Fig 5). Examination with an endoanal coil is especially suitable for demonstrating subtle changes within the sphincters, since these lie close to the coil surface. The spatial resolution provided by either a phased-array or a body coil is probably insufficient to aid in the diagnosis of sphincter abnormalities (60). Rigid endoanal coils are preferred for optimal image quality; the diameter of such coils ranges from 7 to 19 mm (21,61). The diameter used is a compromise between imaging of an effective volume and overcompression of adjacent structures. Muscle relaxants may be used to reduce artifacts due to peristalsis (21).
The optimal sequence for evaluating anal sphincter anatomy and abnormalities has not been established. We routinely use a T2-weighted sequence (eg, fast spin-echo) as our basic sequence. The use of T1-weighted sequences, either standard or dynamic with contrast medium, increase cost, and their superiority over other sequences has not been established. The transverse plane, oriented to be at a right angle to the anal canal, is the most relevant surgically and is supplemented by use of longitudinal planes to provide additional information on the extent of disease (62). Similar to the urethra, the smooth muscle of the internal sphincter is relatively hyperintense, and the striated muscle of the external sphincter, puborectal muscle, and levator ani muscle are relatively hypointense on T2-weighted images.
Endoanal MR imaging is well tolerated by nearly all patients and is easily performed (21). Discomfort is limited and comparable to that at endoanal US, although the procedure is more time-consuming (approximately 30 minutes vs 5 minutes) (21).
Colonic Transit Studies
The colon and rectum operate as a single functional unit, so investigation of constipation usually incorporates assessment of colonic transit. A variety of techniques of varying complexity are available, and the level of information needed largely determines which is chosen. Accurate assessment of segmental transit requires scintigraphy to quantify the passage of radioisotope through the colon (63). This is time-consuming and expensive, however, and a simple assessment of whole gut transit by using radiopaque markers is usually all that is necessary, particularly because the relevance of segmental transit disorders remains controversial. A simple method involves acquisition of a single abdominal image 6 days after radiopaque markers have been ingested. This method provides an overall estimation of whole gut transit (64) and has been validated by comparing such images with radionuclide studies (63).
Evacuation Proctography
Evacuation proctography is a simple radiologic technique that involves imaging of rectal voiding of a barium paste enema. Radiologic studies of rectal evacuation have been performed for nearly 50 years but became more widely utilized after description of a simplified technique in 1984 (65). Although evacuation proctography is now well established, its use is predominantly confined to specialist centers. Furthermore, the role of this technique remains controversial despite several years of clinical use. The examination is also termed defecography, but the evacuation during the test is not associated with any of the colonic reflexes that accompany normal defecation, so this term may be misleading; rather, it is a test of voluntary rectal evacuation. Constipation—namely, difficult or infrequent rectal evacuation—is the main indication for performance of evacuation proctography. Some authors have stressed a role in incontinence, since an obtuse anorectal angle may help identify patients likely to benefit from postanal repair if the anal sphincters appear normal at US. It has been argued, however, that involuntary loss of barium alone may be sufficient for diagnosis, and many investigators believe that evacuation proctography has a limited role in this scenario.
Technique.—Evacuation proctography is a rapid and simple technique to perform. The rectum may be emptied prior to evacuation proctography, either by administering glycerin suppositories or an enema. These maneuvers have been criticized as unphysiologic, but they do standardize the examination if a fixed volume of contrast medium is given. This allows comparison with normal of evacuation time and completeness, as well as with any change on follow-up studies. The passage of stool during the examination may interfere with the visualization of an intussusception.
In general, a prepared examination is more acceptable to both patients and staff. It is generally accepted that the consistency of the contrast medium should approximate that of feces: a barium suspension mixed with either potato starch or methylcellulose. Commercial preparations are also available. The total volume used is variable; some investigators instill contrast medium until a strong urge to evacuate is provoked, whereas others use an identical volume in all cases, for the reasons given earlier (we use 120 mL).
The paste is injected with a syringe into the rectum, with the patient in the left-lateral position on the fluoroscopy table. The injection is continued during withdrawal of the syringe, to mark the anal canal and verge. The table is moved into the upright position, and a commode is placed on the footrest. The commode must incorporate some filtration to prevent screen flare. Four millimeters of copper provides sufficient attenuation (66). Although many authors stress the importance of the more physiologic and sensitive seated position, the examination can be performed in the left-lateral position if a commode is unavailable or if the patient is incontinent, but static values for pelvic floor position are higher (67). It is essential to perform continuous or rapid recording of rectal evacuation by means either of spot imaging or videofluoroscopy. Although spot imaging provides the best spatial resolution, the ability with videofluoroscopy to replay the entire examination at any speed is an invaluable feature if evacuation is rapid or findings are subtle; this is also possible with some digital systems. Patient dose is also lower than that for standard imaging, although newer digital systems allow substantial reduction in dose. A suitable compromise is to videotape the examination with spot images obtained at key events (68). To reduce dose, imaging should be intermittent if evacuation is prolonged.
Normal study.—Based on the findings in 56 asymptomatic patients, Mahieu et al (65) defined five criteria for a normal evacuation proctographic study: increase in anorectal angulation, obliteration of the puborectal impression, wide anal canal opening, total evacuation of contrast medium, and normal pelvic floor resistance. Several subsequent studies with asymptomatic volunteers have revealed a wide range of normal values, and some overlap with pathologic states (66,69). Nevertheless, there is a consensus regarding normal findings, with broad agreement with the description by Mahieu et al.
The proctographic component of the examination can be considered in three stages: the preevacuation, evacuation, and postevacuation stages. The initial lateral view records the preevacuation anorectal configuration and pelvic floor position. The anorectal angle is thought to be important in maintaining continence and is usually measured between the axis of the anal canal and the posterior rectal wall. Although considerable attention has been devoted to this measurement, there is little evidence that it is important. The junction between the rectal ampulla and the anal canal, the anorectal junction, is easy to appreciate at rest. The pubococcygeal line (Fig 13) is traditionally used to define the level of the pelvic floor but may be difficult to identify with a limited field of view, in which case the inferior surface of the ischial tuberosities are used instead. At rest the anorectal junction should be at or just above this plane, and the anal canal should be closed without leakage. The anorectal angle should be approximately 90°. Some investigators advocate the acquisition of views during a "squeeze" maneuver to evaluate the strength of voluntary pelvic floor musculature, during coughing to stress the continence mechanism, and during straining to assess pelvic floor descent. However, the anorectal angle may increase during these maneuvers in up to 30% of normal subjects, which reflects paradoxical pelvic floor contraction to maintain continence (70).
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Modifications to the basic technique.—The technique described in the preceding paragraphs will demonstrate the rectal configuration during evacuation and help determine the rate and completeness of evacuation. It is now well recognized that weakness of the middle and anterior pelvic floor often accompanies posterior weakness, so there may be any combination of cystocele, rectocele, enterocele, sigmoidocele, and gynecologic prolapse (1).
An enterocele is defined as prolapse of the small bowel into the rectogenital space; and a sigmoidocele, as prolapse of the sigmoid colon into this space. These are notoriously difficult to detect clinically. In one study (72) with 300 women, enteroceles were revealed with dynamic cystoproctography in 111, of which 93 (84%) were missed at clinical examination. With standard proctographic techniques, these entities will also be missed, and the authors of that study stressed the benefits of an integrated approach to pelvic floor imaging. To achieve this, the most common proctographic modification is oral administration of a barium suspension approximately 1–2 hours before the procedure to opacify the small bowel (68). Alternatively, a vaginal marker in women can help diagnose prolapse by demonstrating rectovaginal separation during or after evacuation. The best choice is probably a barium paste, because a tampon may inhibit prolapse by splinting the vagina (73). However, enteroceles may develop without substantial rectovaginal separation. In addition, liquid barium can be injected before administration of the paste, to opacify the sigmoid colon and identify a sigmoidocele.
Dynamic cystoproctography is essentially evacuation proctography preceded by cystography (70,72,74). Catheterization of the bladder is performed with a 5-F feeding tube (after manual reduction of a prolapse, if necessary). The bladder is then drained and filled with water-soluble contrast medium (45). Lateral views of the bladder are obtained at rest and during maximal straining (45). The bladder should then be emptied completely, because the space in the pelvic cavity is limited; a cystocoele will prevent formation of an enterocoele and vice versa. To overcome the "crowded pelvis," the cystographic phase should also be performed before rectal filling, because rectal distention elevates the bladder base and may mask a cystocele (1).
Some investigators (75,76) have also introduced water-soluble contrast medium directly into the peritoneal cavity to image the pelvic peritoneal recesses during voiding, a practice that is unnecessarily invasive since the advent of dynamic MR imaging. Evacuation proctography has also been combined with simultaneous cystography, EMG, and intrarectal pressure measurement, but the benefits of these combinations remain uncertain.
Dynamic MR Imaging
Although evacuation proctography is rapid and easy to perform, the modifications needed to image other organs are time-consuming and invasive. Also, the musculature of the pelvic floor is not visualized directly, and irradiation of younger patients is an important factor. To overcome these limitations, MR imaging has been applied to pelvic floor dynamics with promising results, although the experimental nature of this procedure must be emphasized. Initial study results were necessarily compromised by slow acquisition times (77), but advances in MR technology now allow multisection imaging during a single straining effort (2,78,79).
The basic examination requires no patient preparation. Vaginal and rectal lumina may be intubated with a soft catheter to facilitate identification. The patient is positioned supine in the magnet, on protective pads, and the pelvis is imaged at rest by using a rapid sequence (eg, fast spoiled gradient-echo acquisition in steady state). Images may be obtained in sagittal, coronal, and transverse planes. The sagittal plane best demonstrates the relationship of the pelvic viscera to each other and the pelvic floor (Fig 13). Imaging is then repeated while the patient performs a maximal straining effort, which has been practiced with the patient beforehand. The resulting images are best viewed as a cine loop to appreciate organ dynamics.
This is an evolving field, and an optimal technique has yet to emerge. Like cystoproctography, some authors catheterize and fill both the bladder and the rectum and encourage the patient to evacuate within the magnet, an examination that has been termed colpocystorectography and undoubtedly provides the most informative study, at the expense of some inconvenience (54). Direct comparison has been made with proctography, and, not surprisingly, there is considerable discrepancy between results (80). This is probably a consequence of the necessary supine position, which can be overcome by those fortunate enough to have access to a vertical open MR system (81). Normal values will have to be determined for this evolving technique, but a study (82) with 50 asymptomatic individuals found some crossover with values assumed to indicate a pathologic condition. The technique is especially valuable for help in the diagnosis of perineal hernia, because both the herniated bowel (usually the rectum) and the defect in the levator plate can be seen.
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PATHOLOGIC CONDITIONS |
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TOPABSTRACTINTRODUCTIONANATOMYPHYSIOLOGY FUNCTIONAL DIAGNOSTIC TESTS IMAGING TECHNIQUES PATHOLOGIC CONDITIONS CONCLUSIONREFERENCES |
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Urge urinary incontinence.—Patients with symptoms of urge incontinence are unable to prevent urine leakage when they perceive an urge, because of an inability to inhibit bladder contraction (47,87). Urge incontinence may be perceived as stress incontinence if triggered by cough and straining, especially in the absence of normal bladder sensation, and can be caused by detrusor dysfunction in known neurologic disease (detrusor hyperreflexia) or in patients without such disease (detrusor instability). Common causes of detrusor hyperreflexia include spinal cord injury, cerebrovascular accident, Parkinson disease, and multiple sclerosis. Detrusor instability can be caused by irritation, such as that caused by urinary tract infection or radiation-induced cystitis, or no specific cause may be identified (idiopathic urge incontinence). The pathophysiologic characteristics of bladder instability are incompletely understood but may be related to increased sensitivity of the bladder nerve endings. Definitive diagnosis is established with findings from CMG or VUDO, where urine loss due to a nonsuppressible detrusor contraction in the absence of stress incontinence indicates detrusor instability. Ambulatory CMG is possible in patients in whom there is a high index of suspicion but with an apparently stable bladder at CMG or VUDO. Treatment is empiric, relying on behavioral therapy, anticholinergics, or musculotropic relaxants. Surgery, including bladder augmentation or urinary diversion, may be indicated in patients who do not respond to empiric treatment (84).
Stress urinary incontinence.—Stress urinary incontinence is defined as uncontrolled urine leakage during stress or activity such as sneezing, coughing, or exercise. The urodynamic definition is involuntary loss when the intravesical pressure exceeds the maximum urethral closure pressure in the absence of detrusor activity (87). Two types of stress urinary incontinence are identified: genuine stress incontinence, caused by hypermobility of the bladder neck, and the less frequent intrinsic sphincter deficiency, caused by a sphincter defect (88,89).
Bladder neck hypermobility is primarily due to weakened pelvic floor support, which is caused by denervation, musculofascial defects, or both (90–94) secondary to aging, obesity, pregnancy, and vaginal delivery (95,96). Weakening results in ineffective transfer of intraabdominal pressure onto the urethra, preventing closure. Some investigators (24) believe this is due to displacement of the urethra below the pelvic floor, whereas others (12,97) suggest that a lax and movable endopelvic fascia underlying the urethra is responsible.
Intrinsic sphincter deficiency can be caused by sympathetic nerve injury, surgical injury (eg, bladder neck suspension), or trauma (93,94,98). Urodynamics are performed to exclude detrusor instability and voiding difficulties. Urethrovesical junction mobility can be evaluated by VCUG, VUDO, or US (Table 1) (9,38,42, 50,99), and the latter is often preferred because radiation is not involved (50). Neither US nor VCUG can provide simultaneous information on detrusor instability, unlike VUDO. Additional urodynamic tests used for differentiation between genuine stress incontinence and intrinsic sphincter deficiency are urethral pressure profiles, detrusor leak-point pressure measurement, and abdominal leak-point pressure measurement (100).
Therapy for stress urinary incontinence may be conservative (physiotherapy, drugs, or mechanical devices) or surgical. More than 150 surgical procedures have been developed for treatment of stress urinary incontinence. Suspension techniques are based on the concept that urethral descent influences urethral closure (24), whereas sling operations and periurethral bulking agents are used for intrinsic sphincter deficiency, with preference for a sling procedure in women with coexisting hypermobility (84). Artificial sphincters are used if intrinsic sphincter deficiency is unresponsive to other treatments. Despite all efforts, the long-term outcome is suboptimal, which suggests that current diagnostic work-up and/or surgical techniques should be reconsidered (12,101–103). US may be useful for postoperative evaluation (39). Periurethral bulking agents may be visualized by using US and MR imaging, but the imaging appearances cannot predict outcome (104,105).
Future role of imaging in stress urinary incontinence.—The relatively disappointing surgical results together with other factors, such as the emerging new concepts of pathologic mechanisms, have increased the need for more structural information (97). Detailed demonstration of the pelvic floor muscles, urethra, and supporting structures was not possible prior to the development of MR imaging. MR imaging, especially endoluminal imaging, provides a level of detail otherwise unobtainable (8,13,14,52,53). Similar information is obtained, to a more limited extent, with endoluminal US performed with high-frequency transducers. The authors of some encouraging initial reports (43,106,107) have described the use of MR imaging and US for identification of urinary sphincter volume and defects. High-resolution MR imaging can be used to identify thinning of the levator ani muscle and associated paravaginal defects, and dynamic MR imaging can be used to determine urethrovesicular and pelvic floor mobility (53,55,56). At present, these techniques are predominantly performed at specialized centers, with research aimed at further defining the role of the techniques.
Miscellaneous causes of urinary incontinence.—Bladder US can reveal a substantial postvoiding residual in cases of overflow incontinence, which may be secondary to outflow obstruction or autonomic (eg, diabetic) neuropathy. A urethral diverticulum, thought to be secondary to rupture of obstructed periurethral glands after inflammation (108), fills during voiding and empties intermittently, causing dribbling incontinence. A diagnosis established on the basis of imaging findings is most accurate (109). VCUG (51) or double-balloon urethrography can be used to identify contrast medium–filled diverticula only, which is not a prerequisite for US (transvaginal, transperineal) or MR imaging (109). Imaging can also help identify a urinary fistula or ectopic ureter. Most cases of outflow obstruction will be due to prostatic hypertrophy, which is associated with detrusor instability (110).
Constipation
Constipation is the most common reason to request evacuation proctography, although pelvic pain, prolapse (rectal or other), and anal incontinence may be other indications. Chronic constipation is common, accounting for an estimated 2.5 million physician visits per year in the United States (111) and regularly affecting up to 20% of the population. Constipation also has considerable economic impact: In 1987, it was estimated that cathartics were prescribed for 3 million people yearly in the United States, with over $200 million spent on laxatives (112). A study (113) with severely constipated patients found that three-fourths had taken time off work, and one-fifth lost their job.
Constipation is a symptom, not a clinical sign, and is particularly subjective, meaning different things to different people. When asked to define constipation, there is considerable individual variation in response (112). Any adequate definition must include concepts of both infrequent defecation and difficult evacuation. Infrequent stools are usually defined as less than three per week, and straining at stool is considered to be abnormal if it occurs for more than 25% of the time spent in the lavatory. Although constipation is common among uncomplaining subjects, patients presenting to referral centers tend to have worse symptoms and, therefore, real cause for complaint. Constipation is three times more frequent in women, who comprise practically all those with severe symptoms. Physicians often accept patients’ claims that they are constipated, but patients are inaccurate when asked about their bowel frequency, and some even deny the passage of stool when this has occurred. In a study (114) with 224 patients referred because of severe constipation, the authors documented normal examination results in 49, with daily stools in 24. Therefore, objective criteria for constipation, such as slow colonic transit, may be preferable to subjective criteria for diagnosis.
It is clearly inappropriate to examine all patients presenting with constipation, even if this were economically feasible. The physician’s role is to determine symptom severity to select those in whom further investigation is appropriate. It should be remembered that the primary aim of investigation is to guide therapy by sorting patients into treatment-defined groups. At present, the treatment options for severe constipation are limited, and investigation may achieve little other than to confirm symptom severity. It must be appreciated that this is not a field where there is any final histologic arbiter. Functional disorders are difficult to analyze. Interpretation must be cautious and referred to developments in related fields of diagnosis.
The causes of constipation are legion, and most will respond to simple dietary measures once certain underlying causes have been excluded. In particular, an obstructive lesion must be ruled out in the older patient with recent-onset constipation, especially if there are symptoms such as rectal bleeding. Severe constipation in younger patients raises the possibility of Hirschsprung disease or megarectum, both of which may be diagnosed with a water-soluble enema study; dilatation extending to the pelvic floor suggests megarectum, whereas a short segment is seen in Hirschsprung disease (115).
The majority of patients who present with severe constipation have no readily identifiable cause, and it seems reasonable to classify these on the basis of functional disturbance. When the predominant feature is slow colonic transit, the term "idiopathic slow-transit constipation" is used (113). However, others may complain primarily of difficult defecation, with prolonged and unsuccessful straining: "outlet obstruction" or "obstructed defecation." Classification into cases of colonic inertia and those of rectal outlet obstruction is simplistic, especially since there is considerable overlap between the two, but is convenient clinically. For this reason, transit studies and evacuation proctography are frequently requested together.
Proctographic abnormalities can generally be divided into structural and functional groups, which may occur in isolation or combination, and have varying clinical relevance.
Rectocele
Rectocele is diagnosed when an anterior rectal wall bulge occurs during evacuation (Fig 14). Most are not apparent at rest. Rectoceles are common in women because the rectovaginal septum is relatively weak, and rectoceles are likely to be a normal variant (116). However, the association between a large rectocele and difficult evacuation is well recognized (117), and proctography is frequently requested for diagnosis. The relevance of a rectocele to symptoms may be determined by the need for vaginal digitation to empty the rectum (118) and retention of contrast medium within it. A rectocele also may be posterior, where it is more correctly termed a posterior perineal hernia because the defect occurs laterally, through the levator plate rather than the midline. Proctography may be used postoperatively to determine technical success, especially if the subject remains symptomatic (119).
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An enterocele is present if small bowel enters the rectogenital space, passing below the proximal one-third of the vagina in women. This usually occurs at the end of evacuation as a consequence of increased intraabdominal pressure and because a filled rectum or bladder frequently pushes small bowel out of the pelvis (70). Similarly, a sigmoidocele is present if colon enters this space. A cystocele occurs if the bladder base descends below the inferior border of the pubic symphysis (Figs 11, 13) (70).
Pelvic Floor Descent
Parks et al (120) described a syndrome characterized by excessive pelvic floor descent, which was considered to be secondary to pudendal neuropathy. In patients with this condition, the pelvic muscles lose their tone, so that the entire pelvic floor descends excessively and balloons during straining; the syndrome is often with associated rectocele and intussusception. It is generally accepted that proctography provides the most accurate estimate of pelvic floor descent, because with clinical methods a perineometer is used to measure movement of the anal verge during maximum straining and not to the point of opening of the anal canal. Excessive pelvic floor descent can be defined as a resting anorectal junction position of 3.0 cm or more below the ischial tuberosities or as anorectal junction descent of more than 3.5 cm during evacuation.
It is unlikely that this constitutes an isolated syndrome. Although lack of muscular support after childbirth is clearly responsible in some cases, many other patients describe a long history of straining at defecation, which raises the possibility that descent follows chronically increased intrarectal pressure. Because of this, an underlying functional disorder of evacuation should always be considered when excessive pelvic floor descent is encountered.
Functional Abnormality
Some constipated patients find it difficult to empty the rectum irrespective of the volume or consistency of the contents of the rectum, a phenomenon that may be disclosed clinically with inability to evacuate a rectal balloon (121). Evacuation failure may be associated with involuntary contraction of striated pelvic floor musculature, a syndrome termed anismus (122) and also known as inappropriate or paradoxical contraction of the puborectalis muscle. The relevance of this finding is uncertain, because it can be demonstrated in both healthy and incontinent patients (123) and may vanish if recordings had been performed outside the hospital environment (124). The etiology of this condition also is unclear: It may be a learned inappropriate response and related to sexual abuse in some individuals (125). Nevertheless, the clear association with difficult rectal evacuation and the success of biofeedback therapy in a substantial proportion of patients suggests that diagnosis is worthwhile (126).
The pelvic and rectoanal coordination required for defecation is complex and involves both conscious and unconscious pathways. It is probably an oversimplification to suggest that anismus is merely confined to a single muscle group; it is likely that the entire pelvic floor is involved, and the condition may be better termed pelvic floor incoordination (127). For example, some patients may merely fail to generate adequate intrarectal pressure (128), and others may also have a functional urinary obstruction.
Because puborectal dysfunction has been the main focus of the syndrome, a proctographic diagnosis of anismus has conventionally been determined on the basis of visualization of a prominent puborectal impression during voiding coupled with failure of the anorectal angle to open; both are frequently cited signs of anismus. However, there is little evidence that these findings are specific, and simultaneous proctography and puborectal electromyography reveal no correlation between muscular activity and anorectal junction configuration. Instead, it is more appropriate to base a proctographic diagnosis on evacuation failure. Healthy subjects void rapidly and completely, in contrast to patients with anismus, whose evacuation is prolonged and incomplete, a difference that can be quantified proctographically (127). The authors of a study (129) with 24 patients in whom a diagnosis of anismus had been established with multiple clinical and physiologic criteria found that puborectal morphology and anorectal angle did not differ from those in asymptomatic control subjects but that prolonged and incomplete contrast medium voiding during evacuation proctography was highly specific. The time taken to initiate anal canal opening and the rate of evacuation are more relevant than the final percentage of contrast medium evacuated, because most patients will eventually fully empty their rectum if given enough time to do so.
Clinical Relevance
Although proctography has been widely practiced for several years, debate concerning its clinical relevance continues. Much of this derives from the excessive attention that has been devoted to the detailed and complex anatomic measurements that are possible during the procedure. Any rectal configuration occurring during emptying other than that of a symmetrically collapsing tube has been considered abnormal. However, a variety of rectal configurations may be present in asymptomatic patients. Shorvon and co-workers (116) demonstrated low-grade intussusception in 80% of men and 81% of women, which clearly suggests that the finding was of little relevance. In contrast, high-grade intussusception is likely to be abnormal; there is a clear association with difficult evacuation and the solitary rectal ulcer syndrome (a combination of difficult evacuation, rectal prolapse, and ulceration, characterized by specific histologic changes), and surgical repair can ameliorate symptoms (130). However, this does not mean that it is the primary cause of difficult evacuation. In some studies (131,132) with patients whose symptoms were attributed to intussusception, investigators have found that these may persist after surgical repair, which suggests that intussusception is merely a secondary phenomenon. It is easy to imagine how this may occur if an underlying functional disorder results in chronic straining. Similarly, chronic straining may engender rectoceles and enteroceles, both of which are found in association with functional disorders; in a study (133) with 41 patients with difficult evacuation ascribed to rectocele, anismus was found in 29 (71%). Furthermore, in a proctographic study (134) with 58 constipated patients, the only significant difference between patients and control subjects was prolongation of evacuation time and failure to fully empty the rectum, which clearly suggest that functional measurements of emptying are more important than changes in rectal configuration.
There are also perceptual differences between patients. Some have heightened rectal awareness, which may lead to sensations of incomplete evacuation ignored by others. Other patients complain of sensations of rectal fullness despite proctographic evidence that the rectum is empty. For example, it is believed that enteroceles compress the rectum, which prevents evacuation; this opinion is derived from proctographic appearances that suggest rectal blockade, but formal studies of rectal evacuation in these subjects are usually normal (135). This may be because the stretch receptors responsible for sensations of rectal distension lie within the surrounding musculature, allowing them to be triggered by the enterocele sac. This raises the possibility that symptoms are due to the sac itself rather than any secondary effect on rectal emptying.
The importance of excessive pelvic floor descent also is uncertain. Some studies show differences between constipated patients and control subjects, whereas others show no difference between incontinent and constipated patients. It is interesting that although chronic straining is believed to cause pudendal neuropathy, there is no correlation between neuropathy and the degree of descent as assessed with proctography (136).
The main value of proctography is related to the ability to aid in simultaneous diagnosis of structural and functional abnormalities and determine which abnormality is more likely to be relevant (Table 1) (115). Problems with interpretation most often occur when anatomic findings are given undue emphasis, which perhaps allows an underlying functional disorder of defecation to remain unrecognized (137). In general, impaired evacuation suggests that a functional abnormality is the primary cause of symptoms. Given this scenario, any abnormalities of rectal configuration may merely be secondary manifestations, and care should be taken not to operate on the basis of structural proctographic abnormalities alone. For example, the authors of a study (138) with patients undergoing rectopexy for solitary rectal ulcer syndrome found that persistent postoperative symptoms were related to impaired evacuation seen at preoperative proctographic rather than to the presence of any prolapse. This approach will direct patients toward biofeedback therapy rather than surgery, because the latter is unlikely to treat the underlying disorder. Furthermore, biofeedback is less invasive, cheaper, and does not preclude a surgical option in the future.
It has been argued that proctography should be the initial test performed in all patients with severe constipation, including those with slow colonic transit, because this may be a secondary physiologic response to an inability to evacuate (139). This approach ensures that treatment aimed at improving rectal evacuation, such as biofeedback, precedes all other measures (140).
Much of the uncertainty related to the benefits or otherwise of proctography has been generated because of studies where the possibilities of functional diagnoses have been ignored, or where benefit has been assessed in terms of outcome, an approach that inevitably includes assessment of any treatment (141,142). Whether a particular imaging technique can assist clinical understanding and management is perhaps the most relevant question in its assessment (143). When this has been applied to investigations of evacuation proctography, the test has method has been overwhelmingly found to be valuable: In a study (144) of 50 consecutive referrals, the authors found that proctography significantly increased diagnostic confidence, with over 90% of clinicians reporting the test to be useful. To our knowledge, there is no prospective controlled study in which patient outcome both with and without evacuation proctography has been evaluated.
Anal Incontinence
Anal incontinence is common, especially in women, and its prevalence increases with age; 2% of the general population older than 45 years have anal incontinence, and the prevalence increases to 7% in those over the age of 65 years. In retirement homes or hospitals, approximately one-third of individuals have anal incontinence. The prevalence is likely higher because of underreporting. Anal incontinence has a considerable economic impact. In a 1988 study (145), it was estimated that more than $400 million was spent annually on incontinence appliances in the United States alone, and anal incontinence was found to be the second most common cause for placement in a nursing home. Patients generally present with either passive incontinence (anal leakage without awareness) or urge incontinence (inability to defer defecation). The former suggests internal sphincter pathology or impacted stool, whereas the latter most likely indicates external sphincter damage (146). Several grading systems for anal incontinence have been developed, and the simple Parks system is commonly used: Grade 1 is continent, grade 2 is incontinent for flatus, grade 3 is incontinent for liquid stool, and grade 4 is incontinent for solid stool.
Causes of anal incontinence.—Childbirth is the most common cause of anal incontinence and is due either directly to anal sphincter laceration or indirectly to damage to sphincter innervation. Until the advent of endoanal US, it was assumed that neuropathy was the primary cause of obstetric-related incontinence, because impaired pudendal nerve conduction can be demonstrated after vaginal delivery, presumably due to stretch-induced injury (147–150). Anal sphincter laceration was thought to be a relatively rare event because it could be identified clinically in only one of 200 vaginal deliveries (151). However, endoanal US revealed that anal sphincter tears were far more common than was initially assumed. In an early study (152) in women with a diagnosis of neurogenic fecal incontinence, it was revealed that over one-third (four of 11 patients) had also sustained unsuspected anal sphincter tears, and in a further study (153) with 62 women whose incontinence was related to childbirth, external sphincter tears were found in 56 (90%). In a prospective study (22) with 202 nonselected consecutive women examined with endoanal US before and after vaginal delivery, anal sphincter tears were revealed in 28 of 79 (35%) of primiparous subjects and in 21 of 48 (44%) of multiparous subjects. Furthermore, endoanal US evidence of sphincter laceration was associated with symptoms of anal incontinence 6 weeks after delivery, and with evidence of physiologic impairment—namely, reduced anal resting and squeeze pressures. No primiparous woman had a defect before childbirth, and no subject who underwent cesarean delivery developed a new defect, which confirmed that sphincter injury was related to vaginal delivery, especially forceps extraction. Moreover, the study results confirmed that the majority of sphincter tears are overlooked at clinical examination. Incontinence may occur immediately after delivery if trauma is sufficient, but many women present later, presumably because the cumulative effects of multiple deliveries, progressive neuropathy, aging, and menopause overcome their compensation mechanisms. Many are also too embarrassed to complain, or they or their physicians believe that the condition is incurable.
Iatrogenic damage is a relatively common cause of anal incontinence. Sphincter division is unavoidable during fistulectomy and fistulotomy, both associated with subsequent incontinence, but endoanal US has revealed unintentional sphincter trauma following hemorrhoidectomy (154) and manual disimpaction (155). Similarly, in a study (156) with patients undergoing lateral sphincterotomy because of an anal fissure, the incision was often found to be far more extensive than intended, which caused subsequent incontinence. Accidental perineal injury and unwanted anal penetration are other traumatic causes of sphincter damage revealed with endoanal US or endoanal MR imaging (157).
Many incontinent patients will have intact sphincters, however, and, in most cases, their symptoms will be due to idiopathic neuropathy (158). Rarer causes of incontinence with intact sphincters include fibrosis, such as occurs in scleroderma. Anal impaction may also cause overflow incontinence.
Imaging in Patients with Anal Incontinence
Imaging has assumed a central role in the management of anal incontinence because it helps identify those patients with a sphincter tear, which allows selection of individuals likely to benefit from surgery to restore the integrity of the sphincter ring. Physical examination cannot be used for reliable detection of anal sphincter defects (159,160), and although anal canal pressures can help determine whether sphincter function is normal, they cannot indicate whether this is due to loss of sphincter integrity or neuropathy.
Endoanal US.—Discontinuity of the sphincters indicates a tear (Fig 16). The accuracy of endoanal US for the diagnosis of sphincter disruption has been validated both histologically (37) and intraoperatively and approaches 95% (152,161,162). An endoanal US study (161) with 44 patients found that all 23 external sphincter defects and 21 of 22 internal sphincter defects were confirmed surgically. Endoanal US is more accurate than electromyography (152,163–165). Inter- and intraobserver agreement are also very good, with a 
statistic of 0.8 for sphincter disruption (58).
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Three-dimensional endoanal US has recently been described (168) and promises to increase our understanding of anal sphincter dysfunction. It is interesting to note that there are considerable turf battles related to endoanal US: In the United States, endoanal US is usually performed by colorectal surgeons or gastroenterologists, whereas in the United Kingdom approximately half such examinations are practiced by radiologists. The operator’s experience is the most relevant factor, irrespective of specialty.
Endoanal MR imaging.—Endoanal MR imaging is a recent development that may help better delineate external sphincter boundaries (60). The high intrinsic contrast resolution of endoanal MR imaging can accurately delineate the sphincter complex, and the multiplanar capabilities demonstrate the sphincter in surgically relevant planes. Endoanal MR imaging can accurately demonstrate lesions of both the external and the internal sphincter (169, 170) (Fig 17). The authors of a retrospective surgical study (157) with 22 patients with sphincter defects compared anal endosonography and endoanal MR imaging and found MR imaging to be the most accurate method for detection. External sphincter defects were detected with US and endoanal MR imaging in 16 (73%) and 20 (91%) patients, respectively, and internal sphincter defects were detected in 15 (68%) and 17 (77%) patients, respectively. The results of a prospective study (171) with 52 consecutive patients with fecal incontinence suggested that endoanal US and endoanal MR imaging are comparable for detection of external sphincter defects and that endoanal US is superior for detection of internal sphincter defects. The patient population characteristics differed between these two studies, and, in the latter study, the comparison of imaging findings was made in a consensus between the gastroenterologist and the surgeon and was not based on results at surgery.
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TOPABSTRACTINTRODUCTIONANATOMYPHYSIOLOGY FUNCTIONAL DIAGNOSTIC TESTS IMAGING TECHNIQUES PATHOLOGIC CONDITIONS CONCLUSIONREFERENCES |
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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TOPABSTRACTINTRODUCTIONANATOMYPHYSIOLOGY FUNCTIONAL DIAGNOSTIC TESTS IMAGING TECHNIQUES PATHOLOGIC CONDITIONS CONCLUSIONREFERENCES |
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G. S. Sudakoff, F. Quiroz, and W. D. Foley Sonography of Anorectal, Rectal, and Perirectal Abnormalities Am. J. Roentgenol., July 1, 2002; 179(1): 131 - 136. [Full Text] [PDF]
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J. Stoker, E. Rociu, W. R. Schouten, and J. S. Lameris Anovaginal and Rectovaginal Fistulas: Endoluminal Sonography Versus Endoluminal MR Imaging Am. J. Roentgenol., March 1, 2002; 178(3): 737 - 741. [Abstract] [Full Text] [PDF]
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F M Kelvin and D D T Maglinte Extended proctography Imaging, December 31, 2001; 13(6): 448 - 457. [Abstract] [Full Text] [PDF]
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J Stoker and E Rociu Endoanal MRI in anal incontinence Imaging, December 31, 2001; 13(6): 467 - 472. [Abstract] [Full Text] [PDF]
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J.-a. Ryu and B. Kim MR Imaging of the Male and Female Urethra RadioGraphics, September 1, 2001; 21(5): 1169 - 1185. [Abstract] [Full Text] [PDF]
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