DOI: 10.1148/rg.264055133
RadioGraphics 2006;26:1135-1149
© RSNA, 2006
MR Imaging of the Female Urethra and Supporting Ligaments in Assessment of Urinary Incontinence: Spectrum of Abnormalities1
Katarzyna J. Macura, MD, PhD,
Rene R. Genadry, MD and
David A. Bluemke, MD, PhD
1 From the Russell H. Morgan Department of Radiology and Radiological Science (K.J.M., D.A.B.) and Department of Obstetrics and Gynecology (R.R.G.), Johns Hopkins Medical Institutions, 600 N Wolfe St, BLA-B 179 RAD, Baltimore, MD 21287. Presented as an education exhibit at the 2004 RSNA Annual Meeting. Received June 17, 2005; revision requested July 15 and received September 7; accepted September 7. K.J.M. supported by an RSNA Research Seed Grant and the Young Investigator Award from the Society of Computed Body Tomography and Magnetic Resonance. The authors discuss an investigational or unlabeled use of a commercial product, device, or pharmaceutical that has not been approved for such purpose by the FDA. D.A.B. receives research support from Surgi-Vision, Columbia, Md; all other authors have no financial relationships to disclose.
Address correspondence to K.J.M. (e-mail: kmacura{at}jhmi.edu).
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Abstract
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The traditional methods for evaluation of urinary incontinence in women include urodynamics, cystourethroscopy, cystourethrography, and ultrasonography. Magnetic resonance (MR) imaging has not played a major role in the assessment of women with urinary incontinence. However, high-resolution MR imaging allows detailed visualization of the urethral sphincter and supporting ligaments in women and may contribute to the diagnosis and staging of sphincteric incompetence related to intrinsic sphincter deficiency or urethral hypermobility. Both the anatomy and the function of the female urethra can be depicted on MR images.
The spectrum of abnormalities detected at MR imaging in women with stress urinary incontinence are classified as (a) findings related to the urethral sphincter deficiency and (b) defects of the urethral support ligaments and urethral hypermobility. These abnormalities include a small urethral sphincter, funneling at the bladder neck, distortion of the urethral support ligaments, cystocele, an asymmetric pubococcygeus muscle, abnormal shape of the vagina, enlargement of the retropubic space, and an increased vesicourethral angle.
© RSNA, 2006
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LEARNING OBJECTIVES
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After reading this article and taking the test, the reader will be able to:- Describe the anatomy of the urethral sphincter and periurethral attachments that promote continence and can be assessed with MR imaging.
- Discuss techniques for the evaluation of urethral morphology and function with MR imaging.
- Identify the MR imaging findings of urinary incontinence in women.
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Introduction
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Urinary incontinence, defined as involuntary leakage of urine, is one of the most common conditions in the female population that causes significant anxiety and negatively affects the quality of life. Urinary incontinence also has a considerable impact on health care costs. This will be increasing with the predicted longer life expectancy of the aging population. Urinary incontinence affects approximately 50% of American women during their lifetimes with an estimated $26.3 billion annually in societal costs (1).
Two generic conditions cause urinary incontinence: urethral sphincter abnormalities and bladder abnormalities (2). There are three main types of urinary incontinence: stress, urge, and overflow. In stress urinary incontinence, there is urine leakage during the sudden increase of abdominal pressure induced by coughing, laughing, sneezing, or exercising. Stress urinary incontinence is a sphincteric type of incontinence. Urge incontinence and overflow incontinence result from bladder abnormalities such as detrusor overactivity and low bladder compliance. In urge incontinence, there is leakage of large amounts of urine at unexpected times, when patients experience a sudden need or urge to urinate, including during sleep. The main cause of urge incontinence is damage to the nervous system leading to bladder instability, common in the elderly; in patients with multiple sclerosis, Parkinson disease, or Alzheimer disease; and after stroke or pelvic injury. In overflow incontinence, there is unexpected frequent leakage of small amounts of urine with an overdistended bladder. This results from weakening of bladder muscles seen in end-stage neurogenic disease or a blocked urethra. Overflow incontinence is rare in women.
Stress urinary incontinence, which is the focus of this article, as a sphincteric type of incontinence is related to intrinsic sphincter deficiency and urethral hypermobility (2). The common causes include loss of urethral compression and support after pelvic surgery, childbirth, and pelvic trauma; lumbosacral neuropathy; chronic intra-abdominal pressure increase from pulmonary disease; vigorous lifting; straining with bowel movement; and aging with hypoestrogenic state.
Intrinsic sphincter deficiency results from inadequate coaptation and compression due to loss of muscle strength and volume.
In intrinsic sphincter deficiency, there is malfunction of the sphincter itself, which leads to an open vesical neck at rest and a low Valsalva leak point pressure (3).
Urethral hypermobility results from weakening of urethrasupporting structures leading to downwad displacement and rotation of the urethra.
Both conditions lead to stress urinary incontinence, which results in leakage of urine with increase in intra-abdominal pressure when the urethra opens concomitantly, such as during a cough, strain, laugh, or exercise.
With its excellent soft-tissue contrast and multiplanar acquisition, magnetic resonance (MR) imaging enhances the ability to visualize the female urethra and periurethral tissues relevant to urinary incontinence. Urethral pathologic conditions have previously been evaluated with MR imaging by using pelvic phased-array coils (4). Intracavitary MR coils, endovaginal (5–7) and endorectal (8), have subsequently allowed urethral MR imaging with both increased spatial resolution and high signal-to-noise ratio. With the advent of the endourethral coil, ultra–high-resolution MR imaging of the female urethra became possible (9).
The traditional methods for evaluation of women with urinary incontinence include urodynamics with intraabdominal, intravesical, and intraurethral pressure measurements and urine flow analysis, cystourethroscopy, cystourethrography, and ultrasonography (US). MR imaging has not been playing a major role in the assessment of women with urinary incontinence. However, MR imaging with its superior soft-tissue contrast and capability for detailed demonstration of the female urethra, sphincter, and supporting ligaments is able to provide valuable information in the assessment of women with sphincteric incontinence. Demonstration of the morphology of the female urethra and periurethral tissues may contribute to understanding of urinary incontinence. The role of MR imaging in the evaluation of patients with urinary incontinence is expected to be increasing in the future.
This article reviews female urethral anatomy and function as depicted at MR imaging in the context of stress urinary incontinence. The spectrum of abnormalities detected at MR imaging in women with sphincteric-type incontinence is discussed. Findings related to the sphincter deficiency as well as defects of the urethral support system are presented.
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Urethral and Periurethral Anatomy
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Anatomic properties of the urethral sphincter that promote continence are coaptation (mucosal seal, inner wall softness); compression (extracellular matrix, collagen, elastin, urethral smooth muscle, and urethral striated muscle); periurethral support; and neural control (2). Coaptation and the status of the mucosa are best assessed with cystourethroscopy. Neural control can be assessed with sphincter electromyography. The muscular layers of the urethral wall contributing to the compression mechanism and periurethral support can be well assessed with MR imaging, best visualized on T2-weighted images. At the midurethral level, where the urethra has a targetlike appearance (Fig 1), the mucosa and submucosal layers are hypointense, the middle smooth muscle layer is hyperintense, and the outer striated muscle layer (urethral rhabdosphincter) is hypointense (10).
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Figure 1a. Intraurethral MR images of an incontinent 72-year-old woman. The images were obtained with a 14-F endourethral coil (*) and the following parameters: repetition time msec/echo time msec = 3400/68, 2.0-mm section thickness, 2.5-mm section spacing, eight signals acquired, 5 x 5-cm field of view. (a) Axial intensity-corrected T2-weighted fast spin-echo image of the mid-urethra shows a multilayered targetlike appearance: The inner smooth muscle layer (white arrow) has higher signal intensity, whereas the outer layer of low-signal-intensity tissue encircling the smooth muscle represents striated urogenital sphincter muscle (black arrow). The periurethral ligament (black arrowheads) is anterior to the urethra, and the pubourethral ligament (white arrowheads) is posterior to the urethra and anterior to the vagina; these ligaments contribute to the hammocklike support of the urethra. Note the reduction of near-field artifact and the good visualization of the dark mucosa and submucosa around the coil on this intensity-corrected image. (b) Axial intensity-corrected T2-weighted fast spin-echo image of the distal urethra shows the pubourethral ligament (arrowheads) posterior to the urethra and anterior to the vagina. Dark striated muscle encircles the urethra. (c) Axial intensity-corrected T2-weighted fast spin-echo image shows the urethra at the level of the compressor urethrae. Note the fanning of the dark striated muscle (arrows) of the urethral sphincter around the urethra and extending toward the anterior vaginal wall.
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Figure 1b. Intraurethral MR images of an incontinent 72-year-old woman. The images were obtained with a 14-F endourethral coil (*) and the following parameters: repetition time msec/echo time msec = 3400/68, 2.0-mm section thickness, 2.5-mm section spacing, eight signals acquired, 5 x 5-cm field of view. (a) Axial intensity-corrected T2-weighted fast spin-echo image of the midurethra shows a multilayered targetlike appearance: The inner smooth muscle layer (white arrow) has higher signal intensity, whereas the outer layer of low-signal-intensity tissue encircling the smooth muscle represents striated urogenital sphincter muscle (black arrow). The periurethral ligament (black arrowheads) is anterior to the urethra, and the pubourethral ligament (white arrowheads) is posterior to the urethra and anterior to the vagina; these ligaments contribute to the hammocklike support of the urethra. Note the reduction of near-field artifact and the good visualization of the dark mucosa and submucosa around the coil on this intensity-corrected image. (b) Axial intensity-corrected T2-weighted fast spin-echo image of the distal urethra shows the pubourethral ligament (arrowheads) posterior to the urethra and anterior to the vagina. Dark striated muscle encircles the urethra. (c) Axial intensity-corrected T2-weighted fast spin-echo image shows the urethra at the level of the compressor urethrae. Note the fanning of the dark striated muscle (arrows) of the urethral sphincter around the urethra and extending toward the anterior vaginal wall.
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Figure 1c. Intraurethral MR images of an incontinent 72-year-old woman. The images were obtained with a 14-F endourethral coil (*) and the following parameters: repetition time msec/echo time msec = 3400/68, 2.0-mm section thickness, 2.5-mm section spacing, eight signals acquired, 5 x 5-cm field of view. (a) Axial intensity-corrected T2-weighted fast spin-echo image of the midurethra shows a multilayered targetlike appearance: The inner smooth muscle layer (white arrow) has higher signal intensity, whereas the outer layer of low-signal-intensity tissue encircling the smooth muscle represents striated urogenital sphincter muscle (black arrow). The periurethral ligament (black arrowheads) is anterior to the urethra, and the pubourethral ligament (white arrowheads) is posterior to the urethra and anterior to the vagina; these ligaments contribute to the hammocklike support of the urethra. Note the reduction of near-field artifact and the good visualization of the dark mucosa and submucosa around the coil on this intensity-corrected image. (b) Axial intensity-corrected T2-weighted fast spin-echo image of the distal urethra shows the pubourethral ligament (arrowheads) posterior to the urethra and anterior to the vagina. Dark striated muscle encircles the urethra. (c) Axial intensity-corrected T2-weighted fast spin-echo image shows the urethra at the level of the compressor urethrae. Note the fanning of the dark striated muscle (arrows) of the urethral sphincter around the urethra and extending toward the anterior vaginal wall.
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The striated urethral sphincter (urogenital sphincter) is divided into three components: (a) the urethral sphincter surrounding the proximal and mid urethra circularly; (b) the urethrovaginal sphincter with fibers surrounding both the urethra and the vagina; and (c) the compressor urethrae with fibers running from the ischiopubic rami and also originating from the urogenital diaphragm itself to the anterior urethra, where they meet fibers from the opposite side, forming a broad arcing muscle (Fig 2) (11).
Functionally, the compressor urethrae can compress the urethra from its ventral position. Because it approaches the urethra parallel to the ischiopubic rami (at an angle of 130° to the urethra), it additionally can have the effect of pulling the urethral meatus caudally. In combination with the action of the pelvic diaphragm, which elevates the bladder, it assists in elongation of the urethra. The urethral elongation has been found important in providing continence (11).
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Figure 2a. Pelvic MR images of a continent 16-year-old girl. Imaging parameters were as follows: 4000/90, 6.0-mm section thickness, 2.0-mm section spacing, four signals acquired, 18 x 18-cm field of view. (a) Axial T2-weighted fast spin-echo fat-saturated image obtained at the level of the mid symphysis pubis shows the dark outer striated urethral sphincter muscle encircling the midurethra (arrow). R = rectum. (b) Axial image obtained at the level of the inferior pubis shows the low-signal-intensity urethrovaginal sphincter (arrowheads) with fibers surrounding both the urethra and vagina.
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Figure 2b. Pelvic MR images of a continent 16-year-old girl. Imaging parameters were as follows: 4000/90, 6.0-mm section thickness, 2.0-mm section spacing, four signals acquired, 18 x 18-cm field of view. (a) Axial T2-weighted fast spin-echo fat-saturated image obtained at the level of the mid symphysis pubis shows the dark outer striated urethral sphincter muscle encircling the midurethra (arrow). R = rectum. (b) Axial image obtained at the level of the inferior pubis shows the low-signal-intensity urethrovaginal sphincter (arrowheads) with fibers surrounding both the urethra and vagina.
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The continuity of the urethrovaginal sphincter with the compressor muscle implies that they complement one another in compression, retraction, and elongation of the urethra. The urethra is inseparable from the anterior vaginal wall for the distal two-thirds of its course. Its sphincteric function depends on the integrity of the mucosa, submucosa, and smooth muscle layers as well as the striated extrinsic sphincter, which is responsible for compressing the urethra directly via its circular fibers (urethral and urethrovaginal portions) and for pulling it deeper into the anterior wall of the vagina through the arcing fibers of its compressor urethra portion.
By detailed visualization of the urethral muscle, the status of the muscle and its volume can be well assessed with MR imaging. Therefore, MR imaging can contribute important information to the diagnosis of urethral sphincter deficiency.
The urethra lies on a supportive layer that is composed of the endopelvic fascia and the anterior vaginal wall, which provide a hammocklike support. This layer gains structural stability through its lateral attachment to the arcus tendineus fascia pelvis and levator ani muscle (12).
The endopelvic fascia forms two transverse layers of fascia, which are attached laterally to the vertical layer of endopelvic fascia. The anterior transverse layer is called the pubocervical fascia and extends from the pubis anteriorly to the cervix posteriorly and is also laterally attached to the arcus tendineus fasciae, which are areas of condensation of the lateral pelvic fascia.
The endopelvic fascia has condensations forming ligaments of the supporting system of the urethra. MR imaging allows visualization of those ligaments (7). Three groups of ligaments supporting the urethra have been described: (a) the periurethral ligament, a thin hypointense structure originating from the medial aspects of the pubococcygeus muscle and coursing ventrally to the urethra; (b) the paraurethral ligament, a slightly oblique hypointense thin structure connecting the lateral wall of the urethra to the periurethral ligament (Fig 3); and (c) the pubourethral ligament, a hypointense structure connecting the lateral aspect of the urethra and the arcus tendineus fasciae (5).
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Figure 3a. Pelvic MR images of a continent 32-year-old woman. Imaging parameters were as follows: 3800/99, 6.0-mm section thickness, 2.0-mm section spacing, four signals acquired, 20 x 20-cm field of view. R = rectum. (a) Axial T2-weighted fast spin-echo image obtained at the level of the upper urethra shows the paraurethral ligament (arrows) extending from the lateral wall of the urethra (U). (b) Axial image obtained at the level of the mid-urethra shows the periurethral ligament (arrows) extending between the medial aspects of the pubococcygeus muscle (arrowheads) and coursing ventrally to the urethra (U).
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Figure 3b. Pelvic MR images of a continent 32-year-old woman. Imaging parameters were as follows: 3800/99, 6.0-mm section thickness, 2.0-mm section spacing, four signals acquired, 20 x 20-cm field of view. R = rectum. (a) Axial T2-weighted fast spin-echo image obtained at the level of the upper urethra shows the paraurethral ligament (arrows) extending from the lateral wall of the urethra (U). (b) Axial image obtained at the level of the mid-urethra shows the periurethral ligament (arrows) extending between the medial aspects of the pubococcygeus muscle (arrowheads) and coursing ventrally to the urethra (U).
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Pathophysiology of Urinary Incontinence
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The dynamics of the intraabdominal cavity during a Valsalva maneuver (eg, abdominal straining or cough) in a patient with a normal pelvic floor and with pelvic floor relaxation differ. When the bladder is properly positioned in the abdominal cavity, both the bladder and the bladder neck are above the pelvic floor. During a Valsalva maneuver, the intraabdominal pressure rises. This rise is reflected in the vesical pressure. If the bladder is properly suspended, the increased intraabdominal pressure is also reflected in the urethra. For a patient to remain dry, the pressure in the urethra should be equal to or greater than the vesical pressure during bladder filling. When the bladder and urethra are in their proper anatomic place, any pressure increases in the abdominal cavity, from strain or any other cause, will also affect the urethra, preventing leakage (Fig 4a, 4b).
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Figure 4a. Drawings show the pressure distribution at rest and during the Valsalva maneuver when the bladder is well supported and when there is pelvic floor laxity. (a) Pabd is the abdominal pressure measured endorectally or endovaginally, Pves is the pressure measured with an intravesical catheter, Pdet (detrusor pressure) is calculated as Pves – Pabd, Pura is the sum of the urethral pressure – Pabd, and Puc (urethral closure pressure) is Pura – Pves. (b) If the bladder is properly suspended, increased intraabdominal pressure (Pabd) is also reflected in the urethra. For the patient to remain dry, the pressure in the urethra (Pura) should be equal to or greater than the vesical pressure during bladder filling. When the bladder and urethra are in their proper anatomic locations, any pressure increases in the abdominal cavity, from straining or any other cause, will also affect the urethra, thus preventing leakage. (c) When there is pelvic floor laxity, the bladder base and bladder neck are displaced below the pelvic floor level. The increase in abdominal pressure during the Valsalva maneuver will lead to higher pressure in the bladder than in the urethra (Pves > Pura), and the urethral closure pressure (Puc) becomes negative, thus resulting in stress incontinence.
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Figure 4b. Drawings show the pressure distribution at rest and during the Valsalva maneuver when the bladder is well supported and when there is pelvic floor laxity. (a) Pabd is the abdominal pressure measured endorectally or endovaginally, Pves is the pressure measured with an intravesical catheter, Pdet (detrusor pressure) is calculated as Pves – Pabd, Pura is the sum of the urethral pressure – Pabd, and Puc (urethral closure pressure) is Pura – Pves. (b) If the bladder is properly suspended, increased intraabdominal pressure (Pabd) is also reflected in the urethra. For the patient to remain dry, the pressure in the urethra (Pura) should be equal to or greater than the vesical pressure during bladder filling. When the bladder and urethra are in their proper anatomic locations, any pressure increases in the abdominal cavity, from straining or any other cause, will also affect the urethra, thus preventing leakage. (c) When there is pelvic floor laxity, the bladder base and bladder neck are displaced below the pelvic floor level. The increase in abdominal pressure during the Valsalva maneuver will lead to higher pressure in the bladder than in the urethra (Pves > Pura), and the urethral closure pressure (Puc) becomes negative, thus resulting in stress incontinence.
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Figure 4c. Drawings show the pressure distribution at rest and during the Valsalva maneuver when the bladder is well supported and when there is pelvic floor laxity. (a) Pabd is the abdominal pressure measured endorectally or endovaginally, Pves is the pressure measured with an intravesical catheter, Pdet (detrusor pressure) is calculated as Pves – Pabd, Pura is the sum of the urethral pressure – Pabd, and Puc (urethral closure pressure) is Pura – Pves. (b) If the bladder is properly suspended, increased intraabdominal pressure (Pabd) is also reflected in the urethra. For the patient to remain dry, the pressure in the urethra (Pura) should be equal to or greater than the vesical pressure during bladder filling. When the bladder and urethra are in their proper anatomic locations, any pressure increases in the abdominal cavity, from straining or any other cause, will also affect the urethra, thus preventing leakage. (c) When there is pelvic floor laxity, the bladder base and bladder neck are displaced below the pelvic floor level. The increase in abdominal pressure during the Valsalva maneuver will lead to higher pressure in the bladder than in the urethra (Pves > Pura), and the urethral closure pressure (Puc) becomes negative, thus resulting in stress incontinence.
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With aging, after childbearing, or after pelvic surgery, female pelvic floor relaxation may cause the base of the bladder and the bladder neck to fall below the pelvic floor level. The increase in abdominal pressure during a Valsalva maneuver will usually lead to pressures in the bladder being higher than in the urethra (Fig 4c), resulting in stress incontinence (2). Also, pelvic floor laxity and defects in the ligaments supporting the urethra lead to inferior translation and rotation of the urethra, and resulting hypermobility causes urine leak with the increase of intraabdominal pressures.
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Imaging Protocols
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To evaluate the urethral sphincter muscle and the status of the urethral ligaments, high-resolution endocavitary imaging with a small field of view and high imaging matrix is the preferable method of imaging. The endocavitary imaging may include placement of the receiver MR coil in the urethra itself (9), in the vagina (7), or in the rectum (8). We obtained informed consent from our patients who underwent endocavitary imaging.
Intraurethral imaging can be performed with a 14-F Intercept urethral internal MR coil (Surgi-Vision, Columbia, Md) (Fig 5), placed by using a sterile technique, like any other urethral catheter. T2-weighted images are obtained in three planes (axial, sagittal, and coronal). T2-weighted fast spin-echo axial image acquisition parameters are as follows: repetition time = 3000–6300 msec, echo time = 60–75 msec, six to 10 signals acquired, echo train length of 16–32, 2.5–3.0-mm section thickness, 0.5–2.0-mm spacing, field of view = 5–6 cm, 256 x 256, average data acquisition duration = 6 minutes 40 seconds.
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Figure 5. Photograph shows the 14-F endourethral MR coil. The imaging part of the receiver coil (arrows) is inserted under sterile conditions, similarly to placement of a regular urethral catheter.
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Endovaginal and endorectal imaging can be performed with the MRInnervu coil (Medrad, Indianola, Pa). We used this endorectal coil in an off-label manner for endovaginal MR imaging in our patients. Our protocol includes fast spin-echo T2-weighted images in the axial, sagittal, and coronal planes; repetition time = 4000 msec, echo time = 70 msec, three or four signals acquired, 3.0-mm section thickness, 1-mm spacing, field of view = 12–14 cm, 256 x 256.
For the dynamic pelvic floor imaging, fast T2-weighted imaging (single-shot fast spin echo, half-Fourier acquisition turbo spin echo) or gradient-echo imaging can be performed during rest and strain. For good visualization of the rectum and vagina, we instill 120–150 mL of US gel endorectally and 20 mL of US gel endovaginally, and we image with the urinary bladder half full. Pelvic phased-array or torso coils can be used. Our standard protocol includes the following: single-shot fast spin-echo imaging, 
/70, section thickness = 6 mm, spacing = 2 mm, field of view = 26–32 cm, 256 x 193. We obtain eight to 10 images during strain in the sagittal plane in the midline section position for cine display of the urethral motion and bladder neck.
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Imaging Findings in Urinary Incontinence
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Imaging findings in the evaluation of female urethral sphincter anatomy and function can be divided into assessment of the status of the urethral sphincter muscle itself and the status of urethral support structures.
Small Urethral Muscle Volume or a Short Urethra
The urethral muscle volume depends on both the thickness of the muscle, both smooth and striated layers, and the length of the sphincter. The mean normal thickness of the urethral sphincter was reported as 4.3 mm ± 0.9 (total striated and smooth muscle thickness anteriorly at the midurethra level), and the length of the urethra has been reported as 38 mm ± 3 (9). With age, the relative volume of connective tissue increases and the volume of striated muscle and vascular tissue decreases. The decrease in the volume of striated fibers in the sphincter may account for a decrease in its functional capacity. Thinning of the striated sphincter muscle has been reported in patients with stress incontinence (13). Global decreased volume of the urethral sphincter has been reported to contribute to intrinsic sphincteric deficiency. Patients with significant loss of sphincteric muscle or with a short urethra (Fig 6) may suffer from intrinsic sphincter deficiency.
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Figure 6a. Intrinsic sphincter deficiency at urodynamics and a short urethral sphincter at MR imaging in a 55-year-old woman. (a) Coronal T2-weighted fast spin-echo image (4000/90) shows a urethra with a length of 2.5 cm between the internal and external meatus (arrowheads). The average length of the urethra in continent women is 38 mm ± 3. (b) Sagittal single-shot fast spin-echo image (/70) obtained during straining shows the short urethra (arrowheads). Note the minimal funneling at the urethrovesical junction. (c) Coronal MR image obtained in a continent patient for comparison with a shows a 3.8-cm-long urethra (arrowheads).
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Figure 6b. Intrinsic sphincter deficiency at urodynamics and a short urethral sphincter at MR imaging in a 55-year-old woman. (a) Coronal T2-weighted fast spin-echo image (4000/90) shows a urethra with a length of 2.5 cm between the internal and external meatus (arrowheads). The average length of the urethra in continent women is 38 mm ± 3. (b) Sagittal single-shot fast spin-echo image (/70) obtained during straining shows the short urethra (arrowheads). Note the minimal funneling at the urethrovesical junction. (c) Coronal MR image obtained in a continent patient for comparison with a shows a 3.8-cm-long urethra (arrowheads).
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Figure 6c. Intrinsic sphincter deficiency at urodynamics and a short urethral sphincter at MR imaging in a 55-year-old woman. (a) Coronal T2-weighted fast spin-echo image (4000/90) shows a urethra with a length of 2.5 cm between the internal and external meatus (arrowheads). The average length of the urethra in continent women is 38 mm ± 3. (b) Sagittal single-shot fast spin-echo image (/70) obtained during straining shows the short urethra (arrowheads). Note the minimal funneling at the urethrovesical junction. (c) Coronal MR image obtained in a continent patient for comparison with a shows a 3.8-cm-long urethra (arrowheads).
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Defects in the Urethral Sphincter
A diverticulum may cause incontinence by weakening the sphincter wall. Urethral diverticulum occurs due to obstruction of the paraurethral glands with subsequent infection. Urethral diverticula usually develop in the dorsolateral aspect of the middle of the urethra and may or may not communicate with the urethral lumen (14). The diverticulum usually has a horseshoe shape, surrounding the urethra in a circular fashion, or may manifest as a lateral outpouching. Visualization of the neck of the diverticulum may not always be possible; however, when the neck is revealed, its location should be reported to aid the surgical management. T2-weighted images show fluid encircling the urethra (Fig 7). The lack of continuity of the sphincter may contribute to loss of the coaptation and compression needed to maintain continence. However, on its own, urethral diverticulum does not have to cause incontinence. Most female patients with urethral diverticula have normal sphincteric function when presenting with dysuria or urinary tract infection; when the sphincter remains intact above the level of the diverticulum, continence is maintained.
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Figure 7. Circumferential urethral diverticulum in a 41-year-old woman. Axial T2-weighted fast spin-echo image (4000/90) shows an area of fluid signal intensity (arrowheads) around the lateral and posterior urethra.
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Funneling at the Bladder Neck
Widening of the proximal urethra at the vesical neck, called funneling, was found to be the common denominator underlying stress incontinence (15). It is thought to result from weakening of the proximal sphincter muscle and has been implicated in the development of intrinsic sphincter deficiency. Funneling can be seen during rest and can also develop during rotational descent of the urethra with strain (Fig 8). Funneling of the urethra can be attributed to gradual loss of urethral tone from a combination of repeated episodes of traction beyond the continence threshold, progressive postmenopausal atrophy, and gradual loss of pudendal nerve function (15) when the intrinsic closure of the urethra begins to weaken. Funneling of the urethra can be occasionally seen in patients who are continent.
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Figure 8. Funneling in a 36-year-old woman with urinary incontinence. Sagittal single-shot fast spin-echo image (/70) obtained during straining shows urethral hypermobility and widening of the proximal urethra at the vesical neck. Funneling (arrowheads) is associated with weakness of the proximal sphincter.
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Distortion of the Urethral Support Ligaments
Three condensations of endopelvic fascia that form the urethral support ligaments are visualized at MR imaging (Fig 3): the periurethral ligament, paraurethral ligament, and pubourethral ligament (5). Normal ligaments are seen as continuous T2 hypointense bands of tissue stretched tight between the points of attachment. Disruption of the urethral ligaments may be complete or partial. In complete disruption, there is discontinuity of the ligament, complete attenuation of a portion of the ligament, or loss of its attachment (Fig 9). In partial disruption, fluttering of the lax ligament or focal thinning or attenuation can be seen (Fig 10). The failure of the urethral ligaments to hold the urethra in its normal anatomic location behind the pubic bone, where the pubourethral ligaments act as a fulcrum between the bladder and the external urethral meatus, may cause stress incontinence (16).
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Figure 9a. Complete disruption of the periurethral ligament in a 54-year-old woman with urethral hypermobility and incontinence. R coil = endorectal coil. (a) Axial T2-weighted fast spin-echo image (4000/90) shows an irregular and discontinuous left periurethral ligament (arrow). Note the loss of the left vaginolevator attachment (black arrowhead). The right vaginolevator attachment and right periurethral ligament attachment are intact (white arrowhead). (b) Axial MR image obtained at the level of the midurethra shows the discontinuous left periurethral ligament (arrow) and the detached left vaginal wall (black arrowhead). White arrowhead = intact right vaginal attachment.
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Figure 9b. Complete disruption of the periurethral ligament in a 54-year-old woman with urethral hypermobility and incontinence. R coil = endorectal coil. (a) Axial T2-weighted fast spin-echo image (4000/90) shows an irregular and discontinuous left periurethral ligament (arrow). Note the loss of the left vaginolevator attachment (black arrowhead). The right vaginolevator attachment and right periurethral ligament attachment are intact (white arrowhead). (b) Axial MR image obtained at the level of the midurethra shows the discontinuous left periurethral ligament (arrow) and the detached left vaginal wall (black arrowhead). White arrowhead = intact right vaginal attachment.
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Figure 10a. Partial disruption of the periurethral ligament in a 53-year-old woman with mixed urinary incontinence, intrinsic sphincter deficiency, and urethral hypermobility. (a) Axial T2-weighted fast spin-echo image (4100/95) obtained with an endovaginal coil (EV) shows mild fluttering and laxity of the right periurethral ligament (arrow) but no discontinuity. Note the intact and taut left periurethral ligament. Also, note the medially displaced right anterior vaginal wall (black arrowhead) and the intact left vaginal attachment (white arrowhead). R = rectum. (b) Sagittal single-shot fast spin-echo image (/70) obtained during straining shows hypermobility of the urethra, which has rotated into the horizontal plane (arrow), and mild funneling at the urethrovesical junction (arrowhead), which is a sign of proximal sphincter weakness.
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Figure 10b. Partial disruption of the periurethral ligament in a 53-year-old woman with mixed urinary incontinence, intrinsic sphincter deficiency, and urethral hypermobility. (a) Axial T2-weighted fast spin-echo image (4100/95) obtained with an endovaginal coil (EV) shows mild fluttering and laxity of the right periurethral ligament (arrow) but no discontinuity. Note the intact and taut left periurethral ligament. Also, note the medially displaced right anterior vaginal wall (black arrowhead) and the intact left vaginal attachment (white arrowhead). R = rectum. (b) Sagittal single-shot fast spin-echo image (/70) obtained during straining shows hypermobility of the urethra, which has rotated into the horizontal plane (arrow), and mild funneling at the urethrovesical junction (arrowhead), which is a sign of proximal sphincter weakness.
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Hypermobility of the Urethra
The urethra exhibits a ventral concavity as it curves behind the pubic bone. In continent patients, the normal position of the urethra has been shown to be virtually entirely retropubic, meaning that the most inferior portion of the muscular urethra is above or at the inferior pubic level (Fig 11) (17). However, in patients with stress incontinence, there is an inferior translation of the urethra, with the lower segment of the urethra lying below the pubis (Fig 12). The larger the infrapubic component, the more extensive is the defect of the urethral support ligaments and paravaginal fascia. It has been shown that patients with urinary incontinence have more than 40% of the urethral length below the inferior border of the pubis in the supine position at rest (17).
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Figure 11. Normal resting position of the urethra in a 53-year-old woman with urinary incontinence. Sagittal T2-weighted fast spin-echo image (4100/95) obtained with an endovaginal coil shows the normal resting position of the urethra, with the most inferior portion of the sphincter (arrowhead) at the level of the inferior pubis (P). Note the narrow hyperintense retropubic space, which is the distance between the posterior pubis and the anterior urethral wall. B = bladder.
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Figure 12. Inferior displacement of the urethra at rest in a 69-year-old woman with urinary incontinence. Sagittal T2-weighted fast spin-echo image (4100/95) obtained with an endovaginal coil shows inferior displacement of the urethra at rest, with the most inferior portion of the sphincter (arrowheads) below the level of the pubis (P). About one-third of the urethral sphincter is inferior to the pubis. More extensive defects of the urethral support ligaments and paravaginal fascia lead to a larger infrapubic component. Note the widened retropubic space compared with that in Figure 11. B = bladder.
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Rotation of the urethra during strain over 30° from its resting axis defines urethral hypermobility (18). It often accompanies moderate to severe bladder descent. Urethral hypermobility results from laxity of the suburethral supporting structures, the posterior pubourethral ligament, leading to urethral axis rotation from vertical to horizontal (Fig 13), so-called rotational descent. Urethral hypermobility is the most common presentation in patients with stress incontinence. It has been shown that the urethra rotates away from the pubis, initially as a single unit (15). At a critical level of descent, the urethra stops rotating as a single unit, with the anterior wall arrested in its rotational descent (the anterior wall is in direct contact with the pubourethral fascial complex) and the posterior wall continuously rotating away from the pubis, frequently resulting in shearing of the posterior wall from the anterior wall leading to the opening of the internal urethral meatus.
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Figure 13. Urethral hypermobility in a 62-year-old woman with pelvic floor laxity. Sagittal single-shot fast spin-echo image (/70) obtained during straining shows hypermobility of the urethra (arrowheads), which has descended and rotated into the horizontal plane.
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Cystocele
Descent of the bladder base below the pubococcygeal line—which extends from the most inferior portion of the symphysis pubis to the last coccygeal joint and defines the level of the pelvic floor—either at rest or during strain is abnormal. The normal vertical distance between the pubococcygeal line and the bladder base at strain is no more than 1 cm below the line (19). Bladder neck descent of 1 cm or more is called hypermobility of the bladder neck. A cystocele forms when the bladder base descends below the pubococcygeal line (Fig 14). Most research has shown that the location of the urethrovesical junction is an important contributing factor to the overall maintenance of continence. However, continent cystoceles with inferior urethral displacement as far as the introitus have been reported (12). Hence, abnormal descent of the urethrovesical junction and formation of a cystocele alone may not be sufficient to account for incontinence.
Asymmetric Pubococcygeus Muscle
The two striated muscle groups that can potentially increase urethral closure pressure during pelvic muscle contraction are the striated urogenital sphincter muscle and the pubococcygeal portion of the levator ani muscle. Whereas the striated urogenital sphincter muscle increases closure pressure by shortening its circumferentially oriented muscle fibers and constricting the lumen (11), the contraction of the pubococcygeus muscle results in urethral compression against adjacent tissues (20). The pubococcygeus muscle can be well evaluated with MR imaging (Fig 15). Loss of the symmetric appearance of the pubococcygeus muscle and lateral deviation and thinning or complete attenuation have been shown in patients with urinary incontinence (Fig 16) (21). Disruption of the pubococcygeus muscle may influence stress continence, as the additional occlusive force on the urethral wall may be lost, particularly during events associated with an increase in intraabdominal pressure.
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Figure 15. Symmetric pubococcygeus muscle in a 38-year-old woman without urinary dysfunction. Axial T2-weighted fast spin-echo image (3800/99) shows a normal symmetric H-shaped vagina (white arrowheads) and an intact symmetric pubococcygeus portion of the levator ani (black arrowheads). R = rectum.
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Figure 16. Disrupted pubococcygeus muscle in a 68-year-old woman with urinary incontinence. Axial T2-weighted fast spin-echo image (3200/100) shows the pubococcygeus muscle (black arrowheads), which is completely disrupted on the right with a large gap (arrows). Note the asymmetric configuration of the vagina (white arrowheads), which is "dropping" on the right. R = rectum.
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Abnormal Shape of the Vagina
The vagina with maintained paravaginal attachments assumes an H-shaped configuration, as seen on axial images (Fig 15). Alteration of the morphologic features of the vagina may be indicative of paravaginal tears. These tears lead to urinary incontinence by weakening the urethral support mechanism provided by the vagina to the middle and distal portions of the urethra embedded in the anterior wall of the vagina (22). With the loss of paravaginal attachments, the vagina has a flattened appearance due to the detached wall of the vagina being displaced posteriorly. The distance between the lateral vaginal wall and pubococcygeus muscle and the pubic bone may increase.
Enlargement of the Retropubic Space
The retropubic space is defined by the distance between the posterior aspect of the symphysis pubis and the anterior urethral wall. It has been shown that the retropubic space may enlarge in incontinent patients (5) (Fig 12). The enlargement of this space is explained as being a result of the damage to the posterior urethral support mechanism, leading to posterior displacement of the urethra.
Increased Vesicourethral Angle
The vesicourethral angle is best evaluated at MR imaging on sagittal images as the angle between the axis of the urethra and the posterior bladder base. An increase in the vesicourethral angle has been reported in patients with urinary incontinence (5). A posterior vesicourethral angle below 115° is considered normal; however, this angle is variable in both the continent and incontinent populations (23) and is not a reliable marker in pelvic floor assessment.
Standard MR Imaging Report
The standard report from MR imaging examination in a patient with urinary incontinence should include a summary of the status of both the urethral sphincter muscle and the urethral support structures. For the urethral sphincter muscle, the following items should be reported: (a) urethral sphincter length (especially if foreshortened), (b) muscle integrity (muscle disruption, diverticulum), and (c) bladder neck competence during strain (especially the presence of funneling). For the urethral support structures, the following items should be reported: (a) an estimate of ligamentous disruption, (b) the presence of detachment of the vaginal fornix, (c) the degree of urethral hypermobility from the resting position, (d) the presence and size of a cystocele, and (e) asymmetry and defects of the pubococcygeus muscle.
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Conclusions
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Traditional imaging methods in the assessment of patients with urinary incontinence include cystourethroscopy, cystourethrography, and US. Cystourethroscopy is used to assess the coaptation and the status of the urethral mucosa. Cystourethrography allows evaluation of the urethral malfunction (hypermobility, bladder neck funneling, cystocele) but does not allow direct visualization of the sphincteric anatomy. In the setting of urinary incontinence, US can be used to assess the urethral mobility and the status of the internal meatus during strain (24), as well as the presence of diverticulum. Three-dimensional US has been used to evaluate the urethral muscle thickness and volume (25), as well as the pelvic floor and endopelvic fascia (26). The advantages of US are low cost and real-time imaging, but the disadvantages are operator dependence as well as limited tissue penetration that does not allow detailed assessment of the urethral support ligaments. MR imaging allows direct visualization and dynamic evaluation of all the morphologic elements of the sphincteric mechanism in a single imaging session.
The female urethra and its supporting structures work in a balanced relationship contributing to the urinary continence mechanism. In the incontinent patient population, the morphologic status of each anatomic component may vary and different combinations of findings can be observed. The cause of the incontinence is usually multifactorial, and the additional information on the status of the urethral sphincter and supporting ligaments provided by high-resolution MR imaging may contribute to the diagnosis and staging of urinary incontinence in the female population. Dynamic evaluation of the urethral sphincter during strain is possible with MR imaging, and simultaneous functional and morphologic assessment may assist in classification of incontinent patients into hypermobility and intrinsic sphincter deficiency categories, which currently is possible only with urodynamic studies.
Treatment of patients with urinary incontinence depends on the type of sphincter abnormality. MR imaging contributes findings that characterize the urethral dysfunction and may guide the choice of therapy and posttreatment follow-up in the future.
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References
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|---|
- Melville JL, Katon W, Delaney K, Newton K. Urinary incontinence in US women: a population-based study. Arch Intern Med 2005;165:537–542.[Abstract/Free Full Text]
- Blaivas JG, Romanzi LJ, Heritz DM. Urinary incontinence: pathophysiology, evaluation, treatment overview, and nonsurgical management. In: Walsh PC, Retik AB, Vaughan ED, Wein AJ, eds. Campbell’s urology. Philadelphia, Pa: Saunders, 1997; 1007–1043.
- McGuire EJ, Fitzpatrick CC, Wan J, et al. Clinical assessment of urethral sphincter function. J Urol 1993;150:1452–1454.[Medline]
- Hricak H, Secaf E, Buckley DW, Brown JJ, Tanagho EA, McAninch JW. Female urethra: MR imaging. Radiology 1991;178:527–535.[Abstract/Free Full Text]
- Kim JK, Kim YJ, Choo MS, Cho KS. The urethra and its supporting structures in women with stress urinary incontinence: MR imaging using an endovaginal coil. AJR Am J Roentgenol 2003;180: 1037–1044.[Abstract/Free Full Text]
- Aronson MP, Bates SM, Jacoby AF, Chelmow D, Sant GR. Periurethral and paravaginal anatomy: an endovaginal magnetic resonance imaging study. Am J Obstet Gynecol 1995;173:1702–1708.[CrossRef][Medline]
- Tan IL, Stoker J, Zwamborn AW, Entius KA, Calame JJ, Lameris JS. Female pelvic floor: endovaginal MR imaging of normal anatomy. Radiology 1998;206:777–783.[Abstract/Free Full Text]
- Nurenberg P, Zimmern PE. Role of MR imaging with transrectal coil in the evaluation of complex urethral abnormalities. AJR Am J Roentgenol 1997;169:1335–1338.[Abstract/Free Full Text]
- Macura KJ, Genadry R, Borman TL, Mostwin JL, Lardo AC, Bluemke DA. Evaluation of the female urethra with intraurethral magnetic resonance imaging. J Magn Reson Imaging 2004;20:153–159.[CrossRef][Medline]
- Strohbehn K, Quint LE, Prince MR, Wojno KJ, Delancey JO. Magnetic resonance imaging anatomy of the female urethra: a direct histologic comparison. Obstet Gynecol 1996;88:750–756.[CrossRef][Medline]
- Oelrich T. The striated urogenital sphincter muscle in the female. Anat Rec 1983;205:223–232.[CrossRef][Medline]
- DeLancey JO. Structural support of the urethra as it relates to stress urinary incontinence: the hammock hypothesis. Am J Obstet Gynecol 1994;170: 1713–1723.[Medline]
- Athanasiou S, Khullar V, Boos K, Salvatore S, Cardozo L. Imaging the urethral sphincter with three-dimensional ultrasound. Obstet Gynecol 1999;94:295–301.[CrossRef][Medline]
- Blander DS, Rovner ES, Schnall MD, et al. Endoluminal magnetic resonance imaging in the evaluation of urethral diverticula in women. Urology 2001;57:660–665.[CrossRef][Medline]
- Mostwin JL, Genadry R, Sanders R, Yang A. Anatomic goals in the correction of female stress urinary incontinence. J Endourol 1996;10:207–212.[Medline]
- Krantz KE. The anatomy of the urethra and anterior vaginal wall. Am J Obstet Gynecol 1951;62: 374–386.[Medline]
- deSouza NM, Daniels JO, Williams AD, Gilderdale DJ, Abel PD. Female urinary genuine stress incontinence: anatomic considerations at MR imaging of the paravaginal fascia and urethra—initial observations. Radiology 2002;225:433–439.[Abstract/Free Full Text]
- Bergman A, McCarthy TA, Ballard CA, Yanai J. Role of the Q-tip test in evaluating stress urinary incontinence. J Reprod Med 1987;32:273–275.[Medline]
- Yang A, Mostwin JL, Rosenshein NB, Zerhouni EA. Pelvic floor descent in women: dynamic evaluation with fast MR imaging and cinematic display. Radiology 1991;179:25–33.[Abstract/Free Full Text]
- DeLancey JO. Structural aspects of the extrinsic continence mechanism. Obstet Gynecol 1988;72: 296–301.[Medline]
- Kirschner-Hermanns R, Wein B, Niehaus S, Schaefer W, Jakse G. The contribution of magnetic resonance imaging of the pelvic floor to the understanding of urinary incontinence. Br J Urol 1993;72:715–718.[Medline]
- Huddleston HT, Dunnihoo DR, Huddleston PM 3rd, Meyers PC Sr. Magnetic resonance imaging of defects in DeLancey’s vaginal support levels I, II, and III. Am J Obstet Gynecol 1995;172:1778–1782.[CrossRef][Medline]
- Stoker J, Halligan S, Bartram CI. Pelvic floor imaging. Radiology 2001;218:621–641.[Abstract/Free Full Text]
- Huang WC, Yang JM. Bladder neck funneling on ultrasound cystourethrography in primary stress urinary incontinence: a sign associated with urethral hypermobility and intrinsic sphincter deficiency. Urology 2003;61:936–941.[CrossRef][Medline]
- Athanasiou S, Khullar V, Boos K, Salvatore S, Cardozo L. Imaging the urethral sphincter with three-dimensional ultrasound. Obstet Gynecol 1999;94(2):295–301.[CrossRef][Medline]
- Dietz HP, Pang S, Korda A, Benness C. Paravaginal defects: a comparison of clinical examination and 2D/3D ultrasound imaging. Aust N Z J Obstet Gynaecol 2005;45(3):187–190.[CrossRef][Medline]
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Abstract
LEARNING OBJECTIVES
