CC BY-NC-ND
0REVIEW
ARTICLE
Ultrasound in Urogynecology: An Update on
Clinical Application
Ling-Hong Tseng*
Technical advances and the increasing availability of ultrasound has enabled physicians to explore new areas in diagnostic imaging of the pelvic floor structure. Perineal/translabial, transvaginal/introital, and transrectal are among the commonly used routes. The previously developed classical 2D ultrasound is considered the standard technique and currently in use for the evaluation of the position and mobility of the bladder neck, bladder wall thickness, and investigation of new surgical procedures. Color Doppler ultrasound not only spots the vascular flow of the pelvic organs, but it can also demonstrate urine leakage. 3D ultrasound distinguishes in detail the pelvic organs, muscle, and fascial components possibly matching up to magnetic resonance image. 3D ultrasound has been used to identify the urethra, levator ani complex, prolapse, and surgical implants used in continence procedure or pelvic reconstruction surgery. Now that ultrasound has gained popularity in serving as a powerful tool to provide valuable information for physicians to provide their patients with better care, there is a need to give an update on its clinical application in urogynecology.
KEY WORDS — 3D ultrasound, levator ani complex, pelvic floor, pubovisceral muscle, ultrasound, urogynecology
■ J Med Ultrasound 2007;15(1):45-57 ■
Introduction
Ultrasound (US) is not intended to replace clinical history taking or physical examination, but instead offers a better understanding of disease entity. Due to its ease of use, noninvasiveness, and absence of radiation exposure, it is currently the most convenient imaging method available. However, reviews of US images from an independent observer indicate the limitation that only available pictures can be reassessed and the possibility of discrepancy
occurring in between exists, a fact of major operator-dependent bias.
Having understood the weakness, some basic concepts should be kept in mind and the physician should be familiar with the mode of probe and the route of application. Many approaches have been applied for the evaluation of the lower urinary tract, including transabdominal, transvaginal, transrectal, perineal (or translabial), and introital. Because the pubic symphysis creates an acoustic shadow which may conceal the lower urinary tract structure, the
Department of Obstetrics and Gynecology, Chang Gung Memorial Hospital and University of Chang Gung School of Medicine, Taiwan.
*Address correspondence to: Dr. Ling-Hong Tseng, Department of Obstetrics and Gynecology, Chang Gung Memorial Hospital and University of Chang Gung School of Medicine, 5 Fu-Hsing Street, Kweishan, Taoyuan 333, Taiwan. E-mail: 3g7330@yahoo.com.tw
©Elsevier & CTSUM. All rights reserved.
J Med Ultrasound 2007 •Vol 15 • No 1
transabdominal approach is usually used to visualize the pelvic organs and for office measurement of postvoid residual volume.
Three-dimensional (3D) US with simultaneous axial, transverse, and coronal views of pelvic organs clearly display the spatial orientation of the lower urinary tract anatomy, which takes clinical application to a new level. However, 3D US facility usually carries a high cost, and in order to master its skill, the operator should be well experienced in performing traditional US, thus limiting its current use to research settings.
A review of the literature shows that the majority of investigators use different sonographic techniques and measurements, rendering the results ineligible for scientific comparison with other findings obtained in other studies. Without a universal standard, teaching is therefore impossible and imaging techniques will not be utilized appropriately and effectively. Here, I will try to outline the basic and advanced levels of know-how that physicians may use to evaluate themselves or at least apply for providing important information that may help them to take care of their patients better.
Basic techniques
The transvaginal approach may exert excessive pressure and induce a compressive effect on the lower urinary tract [1]. The perineal (translabial) or introital approaches can prevent distortion of the anatomy of the lower urinary tract and are most currently used. The differences between the perineal (translabial) and introital approaches lie in the site where the transducer is placed and in the probe used in the image scanning: the former uses a linear- or curved-array convex probe with a frequency between 3.5 and 5 MHz; the latter (introital) uses a sector endovaginal probe with frequency between 5 and 7.5 MHz. The transducer is placed on the perineum for the perineal (translabial) approach (Fig. 1); while for the introital, it is positioned between the labia minora just underneath the external urethral orifice (Fig. 2). Introital US can get high resolutions of urethra and paraurethral tissues but does not allow as many images to be captured as in the perineal
approach. Both approaches have been proven to be devoid of potential morphologic artifacts resulting from distortion of the bladder neck or urethra
[2]. Some physicians may prefer performing these examinations with the same probes. However, the examination should be performed with low surrounding pressure, thereby allowing the capture of a good quality image.
Image orientation
A midsagittal view is obtained by placing a transducer on the perineum, after covering the transducer with a glove or other rubber material for hygienic reasons. We favor the use of a condom because of its convenience and durable quality. Imaging can be performed in the dorsal lithotomy position or supine position, with the hips flexed and slightly adducted, or in a standing position. We prefer the lithotomy position because that is how a patient is usually prepared in the operation room during most urog-ynecology surgeries and data can be collected by using the same position to avoid positional bias.
Most real-time US scanners with formula enable rotation of sonographic pictures. These scanners can therefore display cranial parts in the upper part of the images (Fig. 3). Although it is the most popular method for presenting lower urinary tract images
[3], there has been disagreement regarding the optimal orientation of images obtained in the mid-sagittal plane. Some physicians like the orientation rotated 90 degrees [4], for instance, cranioventral
Fig. 2 (A) Introital ultrasound mainly focuses on the retropubic area containing the urethra, paraurethral tissue, and bladder. (B) Introital ultrasound picture. BL = bladder; U = urethra; PS=pubic symphysis.
Fig. 3. Perineal ultrasound image and pelvic organs illustrated.
aspects to the left, dorsocaudal to the right. Since any image reproduced in one of the above orientations can be converted to the other by a simple adjusting formula through rotation, the decision of image orientation can be based on the physician's preference.
Required information
Clinical history must be obtained during US examination of the lower urinary tract images. Without detailed history taking, it is impossible to tell what you are looking for. The bladder volume should be
fixed on examination, 200-300 mL [5-7] for the evaluation of dynamic changes of the bladder neck in order to avoid an uncomfortably full bladder and less than 50 mL for the assessment of bladder wall thickness. The method for estimation of bladder volume will be discussed later. The presence of full rectum may impair diagnostic accuracy, and therefore, rectum emptying should be encouraged before examination.
Normal images of the lower urinary tract
On US examination, the following structures and organs should be seen: symphysis pubis, urethra, bladder, vagina, uterus, and rectum. The pubis symphysis is seen as an ovoid-shaped structure with homogeneous hyperechogenic structure (Fig. 4). The bladder wall is smooth and intact in integrity. The content of the bladder should be uniform and echolucent unless there is infection, a blood clot, or even tumor.
The urethra is a tubular structure with a central echolucent area surrounded by an echogenic sphincter. When the scan is deviated a little to the right or left parasagittally, two tiny nodules (ureter papilla) located at the junction of the trigone and bladder can be identified due to peristalsis. The position of the ureteral orifices can be visualized by urine jet from each ureteral orifice (Fig. 5).
Fig. 4. Introital ultrasound image of pubis symphysis (PS).
Fig. 5. Urine jet from ureteral orifice.
Applications
I would like to distinguish clinical applications at two different levels: basic and advanced level. The basic level is what every general urogynecologist should be able to reach; the advanced level is for experts specialized in urogynecology US to match up to.
Basic Level
Estimation of bladder volume or postvoid residual urine
The bladder volume can be determined by either a transabdominal or transvaginal approach, although the accuracy is not reliable for bladder volumes
< 50 mL. In the transabdominal approach, three values, including height (H), depth (D), and width (W), are obtained from two perpendicular planes (sagittal and transverse). In sagittal scanning, H and D correspond to the greatest superior-inferior distance and the greatest anterior-posterior distance, respectively (Fig. 6). The bladder volume can be calculated from the formula, bladder volume (mL) = H x D x W x 0.7 [8]. The approximate error rate of the formula is around 21%. Transvaginal US is an alternative to measuring bladder volume. Horizontal height and vertical depth are obtained on sagittal scanning. The bladder volume can thus be calculated, bladder volume (mL) = H x D x 5.9 -14.6 [9].
Consequently, postvoid residual urine can easily be estimated by US during follow-up in the clinic [10,11]. Patients with overactive bladder syndrome, neurogenic bladder, pelvic prolapse, voiding symptoms, or even after continence surgery need this simple test to address the postvoid residual urine issue.
Bladder wall thickening
The normal bladder wall is no more than 6 mm thick. Abnormalities of the bladder wall include focal or generalized thickening and loss of integrity. Conditions such as infection, pelvic radiation, pelvic surgery, neurologic disease, bladder outlet obstruction, and neoplasm can cause bladder wall thickening. Patients with neurogenic bladder that cause thickened and trabeculated bladder wall or even formation of diverticulum, and elevated postvoid residual urine are specially known to produce such an US finding.
Usually, the choice for conducting measurement of bladder wall thickness is transvaginal or introital US. Measurement of the bladder wall is generally performed after bladder emptying with the probe perpendicular to the mucosa (Fig. 7). Three points need to be located first: the anterior wall, trigone, and the dome of the bladder; then, the mean wall thickness of all three are calculated. Bladder wall thickness greater than 5 mm is of clinical significance and associated with detrusor instability [12,13]. Increase in bladder wall thickness
Fig. 6. (A,B) Transabdominal ultrasound measurement of bladder volume (H x D x Wx 0.7). H = height; D = depth; W = width.
J 1.1 cm
Fig. 7. Measurement of bladder wall thickness in a patient with neurogenic bladder.
likely implies hypertrophy of the detrusor muscle, which may be the cause of symptoms or simply reveals the underlying pathology. In Robioson et al's [13] study of 128 patients, they indicated that transvaginal US assessment of mean bladder wall thickness is a sensitive screening tool and a cutoff of 6.0 mm is highly suggestive of detrusor instability. Nevertheless, we must keep in mind that US only offers a clue and not a diagnosis of detrusor instability. Further research needs to be done to see whether this parameter adds any useful information to dealing with patients with pelvic floor disorder.
Bladder tumors
US is a useful tool for screening and detecting bladder tumors [14,15]. Ultrasonographic pictures of
bladder tumors may present as polypoid, sessile, plaque-like, with regular or irregular surface, and with or without calcification. Transvaginal US has been reported to detect bladder wall invasion or explore sequential changes in cervical cancer patients [16,17]. The moveability of the bladder wall is assessed by the ability of the bladder to slide along the uterine cervix when the probe is pushed up against the bladder from the anterior fornix. Good moveability is considered an indication of intact bladder wall. In Huang et al's series [1 7], they showed the possibility of this application in early detection of bladder wall invasion in cervical cancer patients, which may lead to a better treatment strategy. They indicated that the disruption of the endopelvic fascia, a thickened bladder wall, changes in the bladder mucosa, and interruption of the entire bladder wall were ultrasonographic characteristics, in relation to the sequential stages of bladder wall invasion.
Urethral diverticula
Urethral diverticula are a relatively common finding among women with chronic genitourinary conditions, such as recurrent infections, postmicturition dribbling, and dyspareunia. Transvaginal US has been shown to be effective in evaluating patients with suspected urethral diverticulum [18], a lesion appearing as a single or multiple cystic lesions with hypoechogenicity or mixed echogenicity surrounding the urethra (Fig. 8). US should be the first
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Fig. 8. (A) Urethral diverticulum in a symptomatic woman. (B) Introital ultrasound demonstrates urethral diverticula. BL = bladder; U = urethra; UD = urethral diverticulum; PS=pubic symphysis.
choice for detecting urethral diverticulum due to its handy nature, although some physicians may think otherwise and order voiding cystourethrography, double balloon positive-pressure urethrography, or even magnetic resonance imaging (MRI) for this purpose.
Retropubic hematoma
US can detect retropubic hematoma following retropubic urethropexy or current suburethral sling procedure, especially in patients not recovering satisfactorily from the surgery [19]. Retropubic hematoma is usually seen as an echolucent cyst or as mixed echogenicity located between the symphysis pubis, urethra, and bladder. It is easy to tell if an indwelling Foley catheter was left in place (Fig. 9). US can assess the size and progression of the hematoma and offer valuable information on continuing medical care.
Identification of surgical implant Recent advances in urogynecology include newly invented surgical techniques and materials: autologous, heterologous, or synthetic. Physicians should be familiar with some common continence procedures such as tension-free vaginal tape (TVT; Ethicon, Somerville, NJ, USA), suprapubic arc sling (SPARC; American Medical Systems, Minneapolis, MN, USA), transobturator tape (TOT; American Medical Systems), or prolapse repair surgery (Perigee, American Medical Systems) (Fig. 1 0), because patients may have no idea about what
Fig. 9. Transabdominal ultrasound detects a retropubic hematoma following continence procedure. BL = Foley balloon.
kind of surgery they have undergone, and are thus not aware of the kind of synthetic material that was introduced. US may be able to provide valuable information in this regard, helping to clarify the mode of action of these procedures and assess the exact location of the implant material. Synthetic material is easily visualized posterior to the urethra [20,21] and can usually be identified by tracing their course from the pubic rami laterally to the urethra centrally. US can also improve the accuracy of surgical procedures. As reported in Viereck et al's [22] study of 90 stress incontinent women undergoing Burch colposuspension, intraoperative introital US helped to avoid overelevation of associated postoperative complications without compromising the success of the operation. Auto/heterologous material may also be detected by US, but currently we do not have much information on it.
Bladder
Pubourethral angle
Symphysis pubis
Urethra ■
Upper border of symphysis
Lower border of symphysis
Upper border of symphysis Lower border of symphysis
Fig. 11. Perineal ultrasound measurement methods for the bladder neck (BN) position and the retrovesical angle (. (A) Measurement of BN position with two distances. A rectangular coordinate system is set up with the origin at the inferior border of the symphysis. The x-axis is determined by the central line of the symphysis, which runs between its superior and inferior borders. The y-axis is constructed perpendicular to the x-axis at the inferior symphysis border. Dx is defined as the distance between they-axis and BN, and Dy is defined as the distance between the x-axis and BN. For precise localization of the BN, the upper and ventral point of the urethral wall at the immediate transition into the bladder is used. (B) Measurement of BN position with one distance and one angle. The distance between BN and the inferior border of the symphysis and the angle between this distance line and the central line of the symphysis (pubourethral angle) is measured. The determination of the retrovesical angle (is the same for these two methods.
Fig. 12. Measurements of bladder neck (BN) position performed (A) at rest and (B) on valsalva maneuver.
Position and motility of the bladder neck and proximal urethra
Bladder neck position and motility can easily be assessed by perineal or introital US. Points of reference are the central axis of the symphysis pubis or its inferior-posterior margin [23,24] (Fig. 11). Sometimes, the reference point is difficult to obtain in older women due to calcification of the symphyseal disc. The patient's position can be supine or dorsal lithotomy, with or without full bladder; bladder volume may have little effect on the distance and angle measurements [5,6]. However, a full bladder
is less mobile than an empty one and therefore obscures the finding of pelvic organ prolapse [7].
Measurements are usually performed at rest and on valsalva maneuver (Fig. 12). These two set-ups give some value for assessing bladder neck descent. During the valsalva maneuver, the proximal urethra may rotate to a posterior-inferior position and the extent of rotation can be measured by subtracting the angle of inclination between rest and valsalva. Measurements of the bladder neck and the posterior urethrovesicle angle are illustrated in Fig. 11. Ultrasound findings in stress incontinent women
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R fifr-
Fig. 13. Ultrasound demonstration of bladder neck (BN) funneling.
usually include bladder neck funneling (Fig. 1 3) and hypermobility. However, US is not a diagnostic test for stress incontinence. We know there is no definite range for bladder neck descent and a wide range of overlap is present between normal and abnormal values. The cotton swab test (Q-tip test) [25] is much easier than US for the diagnosis of urethral hypermobility. Many factors such as bladder filling, patient position, catheterization, and amplitude of valsalva maneuver have been shown to influence the US measurements of urethral mobility [5-7,26]. But if we would like to compare pre- and postoperative findings or do a multicenter study of bladder volume, then patient position should be standardized to allow unbiased comparison.
One common phenomenon, the funneling of the internal urethral meatus, may be observed on valsalva and also at rest. Prior reports suggested that funneling was often associated with urine leakage and marked funneling was believed to be in connection with poor urethral closure pressures [26,27] or urethral incompetence. However, based on current scientific evidence, I believe that bladder neck funneling should be viewed as a phenomenon rather than a pathologic diagnosis because the voiding mechanism may be more complex than previously thought.
Color Doppler
Doppler US allows the detection of changes in blood flow and vascular pattern and is now a tool for
Fig. 14. Color Doppler ultrasound reveals blood supply signals in the bladder wall, within and around the urethra (U).
evaluating vascular anatomy and disease entities [28,29]. Color and power Doppler US can reveal blood supply signals in the bladder wall, both within and around the urethra (Fig. 14). One recent study [30] investigated the association of Doppler flow parameters with intrinsic urethral function between subjects with and without urodynamic stress incontinence. They attempted to examine the differences in their urethral vasculature and found that the urethral vasculature contained five main branches of vessels. Despite that, based on the relatively small caliber of the urethra, it is difficult to make any conclusion regarding its clinical application. Another clinical situation is the use of transvaginal color Doppler US to demonstrate jets of urine entering the bladder from ureteral orifices for diagnosing ureteral obstruction. If ureteral jets are absent, the diagnosis
and location of the obstruction would demand further investigation [31].
Advanced Level
Currently, I think that only the 3D US technique belongs to the advanced level category. The reason for this comment is that physicians who are able to display 3D US images are very experienced in capturing 2D US images and familiar with pelvic anatomy. Besides, the 3D US set-up is rather expensive and not every place can afford it. Previous reports concerning 3D US mainly focused on obstetric applications [32]. Nevertheless, physicians in the field of urogynecology are putting in efforts to perform 3D US in delineating pelvic floor anatomy and for functional study. They are trying to contrast 3D with 2D US, which they think cannot disclose certain images that 3D can. Nowadays, plenty of studies focusing on the urethra [33,34], levator ani complex [35,36], paravaginal supports [37], prolapse [38], and synthetic surgical implants have been published [20,39]. I would like to introduce some useful 3D US clinical applications to readers who are interested in this area.
3D Ultrasound
I prefer the transvaginal approach with the transducer placed in the introital area in a midsagittal plane. A single volume obtained at rest with an acquisition angle of 80° or higher will include the entire pelvis. Usually, imaging obtained from this view will encompass the levator hiatus with symphysis pubis, urethra, paravaginal tissues, vagina, and rectum (Fig. 15).
Identification of anterior vaginal wall defect
The International Continence Society defines anterior vaginal wall defect as descent of the anterior vagina so that the urethrovesical junction or any other point on the anterior vaginal wall is < 3 cm from the hymenal ring [40]. The current designation reflects
Fig. 15. 3D US imaging of pelvic floor structure. U = urethra; V = vaginal wall; R = rectum; PV = levator ani complex.
the actual site of vaginal wall prolapse, rather than the structures underlying it (bladder or urethra), and has replaced previously used terms, such as cysto-cele or urethrocele. 3D US may offer valuable information for pre/postoperative evaluation because pelvic examination is unable to detect the actual size of the cystocele. It is no wonder that traditional cys-tocele repair usually carries a high risk of recurrence.
The urethra
Although 3D US can assess the urethra status, its role remains uncertain. Prior studies [41] suggested that 3D US could measure urethral sphincter volume or investigate Doppler flow in urethral vessels [30]. It would be interesting to know if 3D US can identify paraurethral supporting structures such as the pubourethral ligament that current continence surgeries like the suburethral sling procedure would most likely repair.
The levator ani complex
3D US enables the physician to look at the pelvic floor from a perspective view that is possibly more functional than an anatomic consideration. 3D US is able to take measurements of the levator complex and levator hiatus and define the biometry of the pubovisceral muscle and levator hiatus [35-38,42] whose findings are compatible with those by MRI.
Fig. 16. 3D ultrasound images of surgical implant. U = urethra; R = rectum; TOT = transobturator tape.
The major advantages of 3D US are helping in the understanding of the changes in the pelvic floor before/after childbirth, aging process, surgical condition, and paravaginal supports. The other interesting areas are investigating women suffering from chronic pelvic pain or using 3D US to compare the biometry alteration in the pubovisceral muscle before and after physiotherapy.
Identification of posterior vaginal wall defect
Similarly, 3D US may reveal posterior vaginal defect image such as rectocele, enterocele, or a combined defect and provide valuable clinical information for preoperative assessment.
Identification of surgical implants
A variety of surgical implants have propelled urogynecology surgery into a new era. Continence procedures in Taiwan, especially suburethral sling operations such as TVT, SPARC, TOT, or intravaginal slingplasty (IVS; Tyco Healthcare, Norwalk, CT, USA), have become popular in the last 10 years and become accepted as primary anti-incontinence surgeries. A patient undergoing urogynecology surgery with synthetic material implant can be easily evaluated using 3D US (Fig. 16). There is no doubt that 3D US can trace those implants throughout their entire length. Either 2D or 3D US can tell the
difference between a TOT tape and that of TVT or SPARC.
Since urogynecologists tend to use synthetic mesh as surgical implants during pelvic reconstruction surgery or continence procedure, accompanying complications such as mesh erosion or exposure, undue voiding dysfunction, or even migration are not uncommon [43-45]. 3D US can assist in locating such mesh implants for surgical removal if conservative treatment has proven ineffective. In addition, the outcome of periurethral injection (collagen or dextranomer/hyaluronic acid) for treating stress incontinent women, although relatively uncommon in Taiwan, may be followed up by 3D US. Another interesting idea is to use 3D US to follow up the outcome of dextranomer/hyaluronic acid copolymer management of vesicoureteral reflux; with this technique, we would be able to examine the residual injection volume and clinical response.
Conclusions and Future Investigation
Due to easy handling, wide range of availability, noninvasive nature, and absence of adverse effects, US imaging is currently the most popular diagnostic imaging method in urogynecology. Perineal and introital US are the favorite approaches in 2D
imaging, while the transvaginal approach may be more appropriate in constructing 3D imaging based on current facility. However, diagnostic US is highly operator-dependent and only a well-trained operator can maximize its usefulness to the full. Each urogy-necologist is advised to master the "basic level" of US skill as mentioned above and try to catch up to the advanced level where 3D US imaging predominates.
It is my hope that 3D US imaging will eventually establish its application in assessing childbirth-related pelvic floor injury, the condition of paraurethral supporting tissue (e.g. pubourethral ligament), levator ani complex, pre/postoperation status of synthetic implant placement, periurethral injection, and anti-reflux injection, physiotherapy response and other pelvic pathologies (e.g. chronic pelvic pain or interstitial cystitis), or perhaps in connection with electromyography study to enhance the understanding of pelvic floor muscle activity in response to environmental stimuli.
To sum up, there is an urgent need for establishing a 3D US imaging standardization system to make it easier for physicians and researchers to follow, thus allowing scientific data to be collected without bias. In future, with newer software and more supplicated machine models available, US will enable exploration of new frontiers in urogynecology.
Acknowledgments
The author wishes to thank SD Chang, MD, for advice regarding this manuscript and Miss Tracy Lu, GE representative, for her kind assistance in facilitating 3D pelvic floor US. Thanks are also due to Dr. TS Lo for offering some of the surgical implant images.
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