Imaging currently plays a limited role in the investigation of pelvic floor disorders. It is obvious that magnetic resonance imaging has limitations in urogynecology and female urology at present due to cost and access limitations and due to the fact that it is generally a static, not a dynamic, method. However, none of those limitations apply to sonography, a diagnostic method that is very much part of general practice in obstetrics and gynecology. Translabial or transperineal ultrasound is helpful in determining residual urine; detrusor wall thickness; bladder neck mobility; urethral integrity; anterior, central, and posterior compartment prolapse; and levator anatomy and function. It is at least equivalent to other imaging methods in visualizing such diverse conditions as urethral diverticula, rectal intussusception, mesh dislodgment, and avulsion of the puborectalis muscle. Ultrasound is the only imaging method able to visualize modern mesh slings and implants and may predict who actually needs such implants. Delivery-related levator trauma is the most important known etiologic factor for pelvic organ prolapse and not difficult to diagnose on 3-/4-dimensional and even on 2-dimensional pelvic floor ultrasound. It is likely that this will be an important driver behind the universal use of this technology. This review gives an overview of the method and its main current uses in clinical assessment and research.
It has taken more than 2 decades for imaging to develop as a mainstream diagnostic tool in the investigation of female pelvic organ prolapse, urinary and fecal incontinence, and defecation disorders. Physicians have been slow in realizing that clinical assessment alone is a poor tool to assess pelvic floor function and anatomy. Our examination skills are quite simply inadequate, focusing on surface anatomy rather than true structural abnormalities. Because the best procedure in the hands of a highly competent surgeon will be a failure if performed on the wrong patient, it is not at all surprising that recurrence after pelvic reconstructive surgery is common. The problem is not poor treatment–it is poor diagnostics. Sonography is an accepted component of any clinical assessment in both obstetrics and in gynecology–so why should it be any different in urogynecology and female urology?
Imaging techniques can provide immediate objective confirmation of findings obtained on examination. In some instances this can lead to markedly enhanced clinical assessment skills. To give just one example: the missing link between vaginal childbirth and prolapse (major levator trauma in the form of avulsion of the anteromedial aspects of the puborectalis muscle off the pelvic sidewall ) is palpable, but palpation of levator trauma requires considerable skill and teaching, preferably with imaging confirmation. Certainly, diagnosis by imaging is more reproducible than diagnosis by palpation, and it is easier to teach. After all, vision is our primary sensory organ. And suspected levator trauma or abnormal distensibility (ballooning) of the hiatus is by no means the only reason to perform pelvic floor imaging ( Table ).
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Equipment and examination technique
This review will be limited to translabial/transperineal ultrasound, and this is reflected in the following comments on equipment and examination technique. However, many clinical questions can be answered just as well by what some investigators call “introital ultrasound,” a technique that is generally understood to involve the use of front-firing vaginal endoprobes placed in the introitus. Although such probes can provide higher resolutions, there are obvious downsides to their use, especially when it comes to assessing the effect of maneuvers and imaging of the levator ani, and this technique will not be discussed further in this review.
Standard requirements for basic 2-dimensional (2D) translabial pelvic floor ultrasound include a B-mode capable 2D ultrasound system with cineloop function, a 3.5- to 6-MHz curved array transducer and a monochrome videoprinter. In essence, any setup used for imaging of the fetus (or a child’s or adult’s kidney) will be appropriate. We obtain a midsagittal view by placing a transducer (usually a curved array with frequencies between 3.5-6 MHz) on the perineum ( Figure 1 , A) after covering the transducer with a nonpowdered glove, condom, or thin plastic wrap. Powdered gloves should be avoided as they can substantially impair imaging quality due to reverberations. Alcohol wipes are usually considered sufficient for transducer cleaning after removal of gel and debris.
Imaging is performed in dorsal lithotomy position, with the hips flexed and slightly abducted, or in the standing position. Requiring the patient to place her heels close to the buttocks will often result in an improved pelvic tilt. Bladder filling should be specified; usually prior voiding is preferable. The presence of a full rectum may impair diagnostic accuracy and sometimes necessitates a repeat assessment after bowel emptying–especially if there is a degree of fecal impaction. Parting of the labia can improve image quality. The latter will also depend on the hydration state of tissues, which generally is best in pregnancy and poorest in elderly women with marked atrophy. Vaginal scar tissue can also reduce visibility, especially in the posterior compartment, but obesity virtually never seems to be a problem.
The transducer can be placed firmly against the symphysis pubis without causing significant discomfort, unless there is marked atrophy. A cough will part the labia, expel air bubbles and detritus, and ensure good contact between the transducer and tissues. It is essential to not exert undue pressure on the perineum so as to allow full development of pelvic organ descent. The standard midsagittal view includes the symphysis anteriorly, the urethra and bladder neck, the vagina, cervix, rectum, and anal canal ( Figure 1 , B). Posterior to the anorectal junction a hyperechogenic area indicates the central portion of the levator plate. The cul-de-sac may also be seen, filled with a small amount of fluid, echogenic fat, or bowel. Parasagittal or transverse views often yield additional information, eg, confirming urethral integrity, enabling assessment of the puborectalis muscle, and for imaging of mesh implants.
There is no agreement on image orientation, and the published literature contains at least 3 different options. The first published translabial images were either obtained with the perineum at the top and the symphysis pubis on the left or the same rotated by 180 degrees. Other authors have used mirrored versions of the same. The author of this review prefers the original orientation as on conventional transvaginal ultrasound (cranioventral aspects to the left, dorsocaudal to the right). This orientation is very convenient when using 3-dimensional (3D)/4-dimensional (4D) systems as shown in Figure 2 , a representation of a 3D volume of the pelvic floor. The top left represents the midsagittal plane, with the bottom left an axial-plane slice, and the bottom right representing a rendered volume showing the levator hiatus.
In the following paragraphs, I’ll describe the main clinical applications of translabial ultrasound in urogynecologic imaging.
Anterior compartment
As clinicians, we say “cystocele” when we really mean “anterior vaginal wall descent.” Of course, anterior vaginal wall descent usually implies descent of the bladder, ie, a “cystocele,” but behind this term there may hide a number of different conditions. Ultrasound can be very helpful in determining whether it is really the bladder that is descending and in ascertaining the configuration of urethra and bladder neck. The original indication for pelvic floor ultrasound, however, is the assessment of bladder neck mobility and funneling of the internal urethral meatus, both of which are important in women with urinary incontinence. Figure 3 shows the standard orientation used to describe bladder neck mobility. The position of the bladder neck is determined relative to the inferoposterior margin of the symphysis pubis or relative to a system of coordinates based on the central axis of the symphysis pubis. Measurements are taken at rest and on maximal Valsalva, and the difference yields a numerical value for bladder neck descent. Comparative studies have shown good correlations with radiological methods. The reproducibility of measurements of bladder neck mobility are high.
On Valsalva, the proximal urethra will be seen to rotate in a posteroinferior direction to a greater or lesser degree, due to the fact that the urethra and anterior vaginal wall are tethered to the symphysis pubis and the pelvic sidewall. Incidentally, this rotation markedly changes the echogenicity of the longitudinal smooth muscle of the urethra, which becomes isoechoic and less easy to identify, as evident in Figure 3 . Proximal urethral rotation can be measured by comparing the angle of inclination between the proximal urethra and any other fixed axis. Some investigators measure the retrovesical angle (or posterior urethrovesical angle) between proximal urethra and trigone, others determine the angle γ between the central axis of the symphysis pubis and a line from the inferior symphyseal margin to the bladder neck.
There is no definition of normal for bladder neck descent although cutoffs of 20, 25, and 30 mm have been proposed to define hypermobility. Bladder filling, patient position, and catheterization all have been shown to influence measurements and it can occasionally be quite difficult to obtain an effective Valsalva maneuver, especially in nulliparous women who frequently coactivate the levator muscle. Perhaps not surprisingly, publications to date have presented widely differing reference measurements in nulliparous women. I have obtained measurements of 1.2-40.2 mm (mean, 17.3 mm) in a group of 106 stress-continent nulligravid young women of 18-23 years of age. It is likely that methodologic differences account for the above discrepancies, with all known confounders tending to reduce descent.
The etiology of increased bladder neck descent is likely to be multifactorial. The wide range of values obtained in young nulliparous women suggests a congenital component. Vaginal childbirth is probably the most significant environmental factor, with a long second stage of labor and vaginal operative delivery associated with increased postpartum descent. This association between increased bladder descent and vaginal parity is also evident in older women with symptoms of pelvic floor dysfunction.
In patients with stress incontinence, but also in asymptomatic women, funneling of the internal urethral meatus may be observed on Valsalva and sometimes even at rest. Funneling is often (but not necessarily) associated with leakage. Marked funneling has been shown to be associated with poor urethral closure pressures. Other indirect signs of urine leakage on B-mode real-time imaging are weak gray-scale echoes (streaming) and the appearance of 2 linear (specular) echoes defining the lumen of a fluid-filled urethra. Color Doppler ultrasound can directly demonstrate urine leakage on Valsalva maneuver or coughing, if this is desired. Agreement between color Doppler and fluoroscopy was high in a controlled group with indwelling catheters and identical bladder volumes. Color Doppler imaging may also facilitate the documentation of leak point pressures.
Clinical examination is limited to grading anterior compartment prolapse, which we call “cystocele.” In fact, imaging will identify a number of anatomic situations that are difficult, if not impossible, to distinguish clinically. There are at least 2 types of cystoceles with very different functional implications ( Figure 4 ), which were first described in this Journal in the 1970s. A cystourethrocele is associated with above-average flow rates and urodynamic stress incontinence whereas a cystocele with intact retrovesical angle is generally associated with voiding dysfunction and a low likelihood of stress incontinence.
Occasionally, a cystocele will turn out to be due to a urethral diverticulum ( Figure 5 , for a 3D representation of an unusual anterior urethral diverticulum), a Gartner duct cyst, or an anterior enterocele. Urethral diverticula are often overlooked for years in women with recurrent bladder infections and symptoms of frequency, urgency, and pain or burning on voiding, until imaging is undertaken. Urethral structure and spatial relationships are much better appreciated in the axial plane ( Figure 5 ), which is particularly useful in the differential diagnosis of Gartner cyst and urethral diverticulum.
Finally, translabial ultrasound may detect foreign bodies or bladder tumors and can be used to determine residual urine, using a formula originally developed for transvaginal ultrasound. Although detrusor wall thickness has probably been overrated as a diagnostic tool in the context of detrusor overactivity, increased detrusor wall thickness seems associated with symptoms of the overactive bladder, and may be a predictor of postoperative de novo urge incontinence and/or detrusor overactivity after anti-incontinence procedures. As opposed to the situation in men, detrusor wall thickness in women is not predictive of voiding dysfunction.
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