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Published online before print September 19, 2002, 10.1148/radiol.2252011347
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(Radiology 2002;225:433-439.)
© RSNA, 2002

Genitourinary Imaging

Female Urinary Genuine Stress Incontinence: Anatomic Considerations at MR Imaging of the Paravaginal Fascia and Urethra—Initial Observations1

Nandita M. deSouza, FRCR2, O. Joseph Daniels, MS, Andreanna D. Williams, MSc, David J. Gilderdale, PhD and Paul D. Abel, FRCS

1 From the Robert Steiner MRI Unit (N.M.d.S., O.J.D., A.D.W., D.J.G.) and Academic Section of Urology in the Department of Surgery (O.J.D., P.D.A.), Faculty of Medicine, Imperial College of Science, Technology and Medicine, Hammersmith Hospital Campus, DuCane Rd, London W12 0HS, England. From the 2001 RSNA scientific assembly. Received August 8, 2001; revision requested September 28; final revision received May 2, 2002; accepted May 14. Supported by Marconi Medical Systems. Address correspondence to N.M.d.S. (e-mail: n.desouza@ic.ac.uk).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
PURPOSE: To compare, on high-spatial-resolution magnetic resonance (MR) images, the presence and distribution of the paravaginal fascia in continent women and in those with genuine stress incontinence (GSI) to establish its role in the pathophysiology of GSI.

MATERIALS AND METHODS: Eleven continent reference subjects and 10 GSI patients underwent MR imaging with a specifically designed endovaginal receiver coil. A urinary continence questionnaire and urogynecologic clinical examination had been completed. GSI was diagnosed with urodynamic tests. Paravaginal fascial tissue distribution was determined, and the paravaginal fascial volume (PFV) anteriorly associated with the urethra was measured. Retropubic urethral length (UL) in the supine position at rest was compared with its total length and expressed as a percentage ratio. Comparisons of urethral PFV and retropubic UL between reference subjects and the GSI patients were performed by means of two-sample t tests with unequal variances because data were parametric by means of the Shapiro-Francia W' test for normal data.

RESULTS: The paravaginal fascia (connective tissue that contained venous plexus) was a consistent MR imaging feature in all women. Mean urethral PFV was 5.3 cm3 ± 0.6 (SD) in reference subjects compared with 3.5 cm3 ± 2.0 in GSI patients (P = .017). The ratio of the retropubic UL to its total length was 82.6% ± 7.4 in reference subjects compared with 57.4% ± 9.8 in GSI patients (P < .001). There was a weak correlation between urethral PFV and retropubic UL (r = 0.46).

CONCLUSION: There is a significant association between urethral PFV and continence status. GSI patients have a reduced urethral PFV, and greater than 40% of their urethral length lies below the pubis in the supine position at rest. However, the effects of age and hormonal status on urethral PFV remain to be evaluated.

© RSNA, 2002

Index terms: Magnetic resonance (MR), intracavitary coils, 85.121411 • Pelvic organs, 85.92 • Pelvic organs, MR, 85.121411 • Urethra, 851.121411, 851.92 • Vagina, 855, 121411, 855.92


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
Urinary incontinence is a social and hygienic problem that causes embarrassment and anxiety, with serious detrimental effects on the quality of life of many women. It affects at least 3.5 million women in the United Kingdom (1) (14% of women older than 30 years) and about 10 million women in the United States (2). Vaginal childbirth strongly predisposes a patient to urinary incontinence, and menopause is associated with increased frequency (1). As average longevity increases, urinary incontinence will become an increasingly major health-related economic problem.

The main causes of urinary incontinence are genuine stress incontinence (GSI), detrusor instability, and overflow incontinence, or a combination of these factors. GSI is the involuntary loss of urine when intraabdominal (and therefore intravesical) pressure is elevated in the absence of detrusor contraction (3). It is exacerbated by chronically raised intraabdominal pressure, as in overweight individuals and in those with chronic bronchitis and chronic constipation, and it is responsible for about 50%–60% of female urinary incontinence (1).

Currently, the two major theories about the pathophysiology of GSI differ in that the hammock hypothesis emphasizes the role of vaginal supports and fascia in the maintenance of continence whereas the pressure transmission theory omits a role for these supporting tissues. Magnetic resonance (MR) imaging, with its superior soft-tissue contrast, is the ideal imaging modality for demonstrating the fascial tissues that support the urethra. Previous MR imaging studies of GSI relate to pelvic floor musculature and supporting ligaments (4–11) and are largely limited to patients with paravaginal defects (12–14). Other studies that focus on urethral anatomy have shown the urethra to lie more inferiorly in patients with GSI (15). To our knowledge, however, there is no MR description of the fascial supporting tissue of the urethra and anterior vaginal wall because MR imaging with an external phased-array coil lacks sufficient resolution. Commercially available inflatable endovaginal devices (12) cause compression and distortion of the immediately surrounding tissues and therefore are unsuitable.

The goal of this pilot study was to compare, on high-spatial-resolution MR images, the presence and distribution of the paravaginal fascia in continent individuals and in women with GSI to establish its role in the pathophysiology of GSI.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
 REFERENCES
 
The study population of 21 female volunteers (age range, 23–68 years; mean age, 47.4 years) comprised 11 continent subjects and 10 GSI patients. In all symptomatic patients, GSI was diagnosed by means of standardized dual-channel urodynamic tests as a prerequisite for inclusion in the study. Exclusion criteria were those for MR imaging (presence of metal, claustrophobia, pregnancy), detrusor instability, vaginal wall prolapse, previous pelvic floor surgery or irradiation, and neurologic problems that affect bladder and lower limb function. Approval for this study was given by the local research ethics committee, and all individuals gave written informed consent before investigation.

All asymptomatic and symptomatic individuals underwent detailed clinical assessment, including relevant medical, gynecologic, and surgical histories. Standardized reproductive and urinary continence questionnaires (16,17) were used that also noted parity and use of hormone-based preparations (oral contraceptive pill and hormone replacement therapy). Before imaging, digital pelvic examination was performed by a urologist to exclude prolapse. Clinical characteristics of the study population are shown in Table 1. It was difficult to match the continent and incontinent women for age, parity, or menstrual or hormonal status because nearly all parous postmenopausal individuals interrogated for possible recruitment to the study admitted to some degree of incontinence. The asymptomatic subjects therefore were used as a reference group.


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  		TABLE 1. Clinical Characteristics of Study Group

 
Imaging with Endovaginal Coil
A specifically designed rectangular (80-mm-long x 35-mm-wide) receiver coil mounted on an acetal homopolymer (Delrin; DuPont de Nemours, Dordrecht, the Netherlands) solid matrix (Fig 1) was positioned in the longitudinal axis of the vagina after digital pelvic examination. Although the coil was rigid, it was 8 mm thick to avoid a compressive effect on the anterior and posterior vaginal walls and to limit tissue distortion. The coil was attached to a 10-cm-long tubular acetal homopolymer handle, which was immobilized in an external clamp stand with its base positioned under the patients’ thighs (18). Patients indicated only minor discomfort during coil insertion and removal while the coil was passing through the introitus, but once in place it was well tolerated even in sexually inactive postmenopausal women.



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  		Figure 1. Endovaginal coil.

 
Patients were encouraged to avoid caffeinated beverages from 2 hours before imaging to reduce diuresis and were asked to empty their bladder immediately before imaging. Imaging was performed with the patient supine with a 0.5-T MR imager (Apollo; Marconi Medical Systems, Highland Heights, Ohio). MR imaging was performed with the following pulse sequences: T1-weighted spin echo (840/20 [repetition time msec/echo time msec]), T2-weighted fast spin-echo (4,000/88 [effective], echo train length of 16), and short inversion time inversion-recovery (2,000/30/107 [inversion time msec]). For T1-weighted sequences, an echo time of 840 msec was required to image the entire length of the vagina in transverse sections. Transverse 3.5-mm-thick contiguous sections with a 12-cm field of view were obtained with a 128–192 x 256 matrix and one to two signals acquired. Additional sagittal and coronal T2-weighted fast spin-echo images were obtained as necessary.

The endovaginal coil (Fig 1) allowed acquisition of high-spatial-resolution MR images (pixel size, 0.6 x 0.5 mm) with high soft-tissue contrast (contrast-to-noise ratio for urethral PFV on short inversion time inversion-recovery images, 16.0 ± 4.5 [mean ± SD]) for assessment and measurement of PFV and urethral length. The short inversion time inversion-recovery acquisitions ensured that extrafascial adipose tissue was not included in the measurements.

Image Analysis
Images were evaluated by an experienced radiologist (N.M.d.S.). Layers of differing signal intensity of the vaginal wall and urethra were identified on T2-weighted images and compared with previously published data (8). The presence of high-signal-intensity tissue and its extent in relation to the urethra (enveloping or extending lateral to urethra) were documented. All measurements involving paravaginal fascial tissue (comprising connective tissue containing a venous plexus) were made on transverse short inversion time inversion-recovery images, while those involving urethral length (UL) were performed on T2-weighted sagittal fast spin-echo images. Images acquired in the coronal plane were used to corroborate the presence and distribution of varying structures.

On T2-weighted images, a high-signal-intensity layer of mucus or secretion was seen immediately surrounding the endovaginal coil. Surrounding this, from internal to external, three vaginal wall layers could be identified: a low-signal-intensity inner layer, an intermediate-signal-intensity middle layer, and a low-signal-intensity outer layer. These correspond to layers of squamous keratinized epithelium, lamina propria (submucosa) of loose connective tissue, and a muscular layer, respectively (8).

Paravaginal fascial volumes related to the bladder neck and urethra (urethral PFV) were measured from the level of the bladder neck (urethrovesical junction) to the level of the external urethral meatus. Regions of interest were drawn around the high-signal-intensity fascial tissue associated with the anterior vaginal wall (anterior to a coronal section centrally through the vaginal lumen) and the urethra (Fig 2a). Area on each section was computed with the computer software and multiplied by section thickness to obtain volume. Images were analyzed by two independent observers (one experienced radiologist [N.M.d.S.] and one surgical resident [O.J.D.]) who were blinded as to whether images were from a reference or symptomatic subject, and interobserver variability was calculated. The results of measurements by the experienced observer were used for statistical analysis.



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  		Figure 2a. Quantification of PFV and urethral position. (a) Transverse short inversion time inversion-recovery MR image (2,000/30/107) through the level of the bladder neck shows demarcated regions of interest around the high-signal-intensity fascia anteriorly and laterally. (b, c) Sagittal T2-weighted fast spin-echo (4,000/88 [effective], echo train length of 16) midline MR images. Total UL is measured from bladder neck to level of urethral meatus (arrows). In b, a line from the posterior inferior point of the pubis perpendicular to the long axis of the retropubic urethra demarcates the length of the retropubic urethra. In c, a line from the posterior inferior point of the pubis was drawn through the curved urethra such that the anterior and posterior ULs were equal below the line. A = anterior, P = posterior.

 


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  		Figure 2b. Quantification of PFV and urethral position. (a) Transverse short inversion time inversion-recovery MR image (2,000/30/107) through the level of the bladder neck shows demarcated regions of interest around the high-signal-intensity fascia anteriorly and laterally. (b, c) Sagittal T2-weighted fast spin-echo (4,000/88 [effective], echo train length of 16) midline MR images. Total UL is measured from bladder neck to level of urethral meatus (arrows). In b, a line from the posterior inferior point of the pubis perpendicular to the long axis of the retropubic urethra demarcates the length of the retropubic urethra. In c, a line from the posterior inferior point of the pubis was drawn through the curved urethra such that the anterior and posterior ULs were equal below the line. A = anterior, P = posterior.

 


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  		Figure 2c. Quantification of PFV and urethral position. (a) Transverse short inversion time inversion-recovery MR image (2,000/30/107) through the level of the bladder neck shows demarcated regions of interest around the high-signal-intensity fascia anteriorly and laterally. (b, c) Sagittal T2-weighted fast spin-echo (4,000/88 [effective], echo train length of 16) midline MR images. Total UL is measured from bladder neck to level of urethral meatus (arrows). In b, a line from the posterior inferior point of the pubis perpendicular to the long axis of the retropubic urethra demarcates the length of the retropubic urethra. In c, a line from the posterior inferior point of the pubis was drawn through the curved urethra such that the anterior and posterior ULs were equal below the line. A = anterior, P = posterior.

 
On transverse T2-weighted MR images, the urethra appeared as a discrete structure with a characteristic targetlike appearance. We identified the following layers on MR images that have been previously correlated with histologic findings (8): a central high-signal-intensity fluid that demarcated the lumen and mucosa was surrounded by a hypointense inner zone (submucosa), a relatively thick hyperintense middle ring (longitudinal and circular smooth muscle), and a thinner hypointense outer ring (striated urogenital sphincter muscle) (8).

With use of a midsagittal section, a line from the most posterior inferior point of the pubis perpendicular to the long axis of the retropubic urethra was drawn through the urethra (Fig 2b). In cases where there was substantial curvature of the urethra, a line was drawn from the posterior inferior point of the pubis through the urethra such that anterior and posterior urethral lengths were equal below the line (Fig 2c). Retropubic UL was measured from the urethrovesical junction to this line and expressed as a percentage ratio to the total UL (measured from the urethrovesical junction to the external urethral meatus).

Statistical Analysis
A statistical software package (Unistat, version 4.53; Unistat, London, England) was used for analyses. Comparisons of urethral PFV and retropubic UL between the reference subjects and GSI patients were performed with two-sample t tests with unequal variances because both sets of data were found to be parametric by means of the Shapiro-Francia W' test for normal data. Bland-Altman analysis was performed to detect significant interobserver variability. A P value less than .05 was considered to indicate a statistically significant difference. Another statistical software package (SPSS, version 10; SPSS, Chicago, Ill) was used to compute the Bland-Altman scatterplot with corresponding 95% limits of agreement.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
Paravaginal Fascia: Volume and Distribution
On both T2-weighted and short inversion time inversion-recovery MR images, the paravaginal fascia (connective tissue containing venous plexus) was identified as a hyperintense structure surrounding the vaginal wall anteriorly, laterally, and posteriorly with variable thickness. The high signal intensity of this tissue was likely a result of its vascularity.

The presence of paravaginal fascia was a consistent MR imaging feature in all women, regardless of age, parity, body mass index, hysterectomy, hormonal use, or reproductive or continence status. Its distribution was variable and appeared to be bulkier around the upper third of the vagina.

The paravaginal fascia extended anteriorly to envelope the urethra totally in 73% (eight of 11) of reference subjects and 20% (two of 10) of GSI patients or laterally in 27% (three of 11) of reference subjects and 30% (three of 10) of GSI patients. Thus, extension of paravaginal fascia either totally or laterally around the urethra was present in all reference subjects but in only 50% (five of 10) of GSI patients (Fig 3). The mean urethral PFV was reduced in GSI patients (3.5 cm3 ± 2.0) compared with that in reference subjects (5.3 cm3 ± 0.6, P = .017) (Table 2, Fig 4).



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  		Figure 3a. Distribution of urethral PFV in reference subjects and GSI patients. Transverse short inversion time inversion-recovery MR images (2,000/30/107) through the middle of the urethra in (a, b) two reference subjects and (c) a patient with GSI show the targetlike appearance of the urethra (arrowheads) in cross section. c = coil, r = rectum. The paravaginal fascia (arrows) surrounds the urethra in a and extends laterally around the urethra in b. In c, there is no substantial fascia in relation to the urethra.

 


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  		Figure 3b. Distribution of urethral PFV in reference subjects and GSI patients. Transverse short inversion time inversion-recovery MR images (2,000/30/107) through the middle of the urethra in (a, b) two reference subjects and (c) a patient with GSI show the targetlike appearance of the urethra (arrowheads) in cross section. c = coil, r = rectum. The paravaginal fascia (arrows) surrounds the urethra in a and extends laterally around the urethra in b. In c, there is no substantial fascia in relation to the urethra.

 


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  		Figure 3c. Distribution of urethral PFV in reference subjects and GSI patients. Transverse short inversion time inversion-recovery MR images (2,000/30/107) through the middle of the urethra in (a, b) two reference subjects and (c) a patient with GSI show the targetlike appearance of the urethra (arrowheads) in cross section. c = coil, r = rectum. The paravaginal fascia (arrows) surrounds the urethra in a and extends laterally around the urethra in b. In c, there is no substantial fascia in relation to the urethra.

 

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  		TABLE 2. Urethral PFV in Study Population

 


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  		Figure 4. Box plot shows median (middle line of box), quartiles (top and bottom lines of box), upper adjacent value (upper whisker), and lower adjacent value (lower whisker) for urethral PFV (uPFV) in reference subjects compared with GSI patients. Note that the upper adjacent value is equal to the minimum of the (a) upper quartile plus 1.5 times the interquartile range and (b) maximum observation. The lower adjacent value is equal to the maximum of the (a) lower quartile minus 1.5 times the interquartile range and (b) minimum observation.

 
Results of Bland-Altman analysis to evaluate interobserver variability between the urethral PFV measurements of the experienced radiologist (observer 1) and the nonradiologist (observer 2) indicated no significant difference (P = 0.19 [paired t test comparing the differences between the measurements of each observer]). The findings with this analysis are shown in Table 3 and Figure 5.


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  		TABLE 3. Bland-Altman Analysis of Urethral PFV Measurements

 


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  		Figure 5. Bland-Altman scatterplot for interobserver variability in measurements of urethral PFV. Interobserver differences in urethral PFV plotted against average urethral PFV for observer 1 (Obs1) and observer 2 (Obs2) do not show significant variability.

 
In the reference group, there was a significant difference in urethral PFV between nulliparous and parous individuals (5.8 cm3 ± 0.5 and 5.0 cm3 ± 0.7, respectively; P = .049). There were no differences in urethral PFV between reference subjects being treated with oral contraceptive pills and those who were not (P = .42) or between GSI patients being treated with hormone replacement therapy and those who were not (P = .62). Also, there were no differences between GSI patients who had undergone hysterectomy and those who had not (P = .87). However, the number of women in each group was small (Table 1).

Urethra
Sagittal MR images showed the urethra throughout its entire length. The mean UL on MR images was 3.0 cm ± 0.4 for the two groups individually. However, there was a significant difference in retropubic UL between the two groups (reference subjects, 82.6% ± 7.4; GSI patients, 57.4% ± 9.8; P < .001) (Table 4; Figs 6, 7).


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  		TABLE 4. Percentage Ratio of Retropubic UL to Total UL in Study Population

 


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  		Figure 6. Box plot shows median (middle line of box), quartiles (top and bottom lines of box), upper adjacent value (upper whisker), and lower adjacent value (lower whisker) for percentage ratio of retropubic UL to total UL in reference subjects compared with GSI patients. Note that the upper adjacent value is equal to the minimum of the (a) upper quartile plus 1.5 times the interquartile range and (b) maximum observation. Lower adjacent value is equal to the maximum of the (a) lower quartile minus 1.5 times the interquartile range and (b) minimum observation.

 


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  		Figure 7a. Sagittal T2-weighted fast spin-echo (4,000/88 [effective], echo train length of 16) midline MR images depict urethral position in (a) a reference subject and (b) a GSI patient. In a, the urethra is virtually entirely retropubic in position. In b, the lower segment of the urethra lies below the pubis. A = anterior, P = posterior, b = bladder, c = coil, r = rectum, s = symphysis pubis. Arrows denote the position of the external urethral meatus.

 


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  		Figure 7b. Sagittal T2-weighted fast spin-echo (4,000/88 [effective], echo train length of 16) midline MR images depict urethral position in (a) a reference subject and (b) a GSI patient. In a, the urethra is virtually entirely retropubic in position. In b, the lower segment of the urethra lies below the pubis. A = anterior, P = posterior, b = bladder, c = coil, r = rectum, s = symphysis pubis. Arrows denote the position of the external urethral meatus.

 
There was no significant difference in retropubic UL between nulliparous and parous reference subjects (81.8% ± 8.4 vs 83.1% ± 7.5, respectively; P = .79) or between GSI patients with and those without hysterectomy (57.8% ± 4.5 vs 57.0% ± 13.9, respectively; P = .91) (Table 4). For the entire cohort, there was a weak positive correlation between urethral PFV and retropubic UL (Pearson correlation coefficient r = 0.46, P = .02).


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
REFERENCES
 
Findings in this study demonstrate that GSI patients have a significant reduction in volume of the fascial tissues of the anterior vaginal wall related to the urethra. The inferior displacement of the urethra in relation to the vagina may in part be responsible for these differences, resulting in less fascial support to the urethra. These findings are consistent with the hammock hypothesis (19–21) of female urinary continence: Support of the bladder neck and urethra is critical in maintaining continence, particularly during periods of raised intraabdominal pressure. The structures responsible for this are held together by a connective tissue "glue" that plays a vital role (22). The paravaginal fascia is likely to contribute to this adhesive glue function.

Support for the bladder neck and urethra is also provided by the pubovesical and pubourethral ligaments, which maintain the proximal two-thirds of the urethra in an intraabdominal position. The pressure transmission theory is that continence during exertion depends on the correct position of the proximal urethra together with an intact urethral sphincter mechanism. Any increase in intraabdominal pressure is transmitted concurrently to the bladder and the proximal urethra, which normally lie above the pelvic floor, to prevent leakage. However, this theory does not take into account the supporting role of the fascial tissues in maintaining urethral position.

Parturition causes damage to and tearing of paravaginal connective tissue along with muscular and neuromuscular injuries (23). These result in fascial defects, and incontinence develops through loss of anterior vaginal wall support for the bladder neck (20,24). This finding was substantiated in the current study by the significant difference in urethral PFV between nulliparous and parous reference subjects. It is also likely that there is a major effect of aging on the parameters measured, but it was not possible to separate this effect because of the age bias of the GSI patients.

A comparison between the MR imaging appearances of the paravaginal tissues and histologic findings in patients undergoing radical hysterectomy shows that the high-signal-intensity layer on T2-weighted MR images reflects connective tissue and smooth muscle cells in a highly collagenized vascular matrix (25 and our unpublished observations). The nature of periurethral connective tissue has been shown previously (26) to be different in continent and incontinent individuals. Premenopausal nulliparous women with GSI have substantially less collagen in their periurethral tissues and a decrease in the ratio of type I (the predominant type) to type III collagen compared with that in continent control subjects (26). Sayer et al (27) found abnormal cross linking of collagen fibrils in the pubocervical fascia of women with GSI, which suggested it was weak. An effect of aging on collagen is also likely (28).

Apart from vaginal supports, the hammock hypothesis refers to the urethral sphincter mechanism as consisting of "internal" and "external" sphincters. The internal sphincter lies at the level of the urethrovesical junction, where closure is determined by the detrusor loop. The external sphincter consists of three elements. The proximal part is a circular band of muscle. It attaches distally to the vaginal wall as the urethrovaginal sphincter. The most distal part attaches to the perineal membrane as the compressor urethrae. The pressure transmission hypothesis of female urinary continence (19) is that the urethral sphincter is divided into "intrinsic" and "extrinsic" portions. The intrinsic part consists of epithelial, vascular, connective, and muscular elements. On T2-weighted MR images, we recognized the bulk of the urethra as a homogeneous hyperintense band of smooth muscle around the central lumen. The low-signal-intensity layer that surrounds this smooth muscle layer represents outer circular striated muscle in a dense connective tissue. This finding confirms the findings of others (6,8,15); the internal-external or extrinsic-intrinsic terminology represent arbitrary divisions.

MR imaging offers new prospects for improving understanding of pelvic support, but imaging with the patient in the supine position introduces changes from the normal upright position because of lack of gravitational effects. In this series, the average UL (3.1 cm) is less than that generally reported in textbooks of anatomy, gynecology, or urology, or in the literature (4 cm). This discrepancy may be due to its slight anterior curvature on MR images and the straightening and elongation of the urethra that occurs during surgical and cadaveric measurements.

Women with GSI are said to have hypermobility of the urethra and bladder neck that is demonstrable clinically. Fielding et al (3) compared MR images of women in sitting and supine positions. They reported that with a Valsalva maneuver in GSI patients, the average descent of the bladder neck was 2.2 cm below the pubococcygeal line (an arbitrary line from the inferior border of the pubic symphysis to the tip of the coccyx) in the sitting position versus 1.6 cm in the supine position. In continent women, the pelvic floor was much more stable; average descent of the bladder neck was 0.8 cm in the sitting position and 0.24 cm in the supine position. This implies a laxity of the pelvic floor in women with GSI. Although our study was performed with patients in the supine position at rest without a Valsalva maneuver, our results showed a highly significant difference between GSI patients and reference subjects in urethral position relative to the pubis and the important role of urethral support in the continence mechanism. As in other studies (3,29), parity and hysterectomy status in our study population did not significantly affect urethral position.

A major limitation of our study is the use of a reference group that is not age matched so that no true "control subjects" were available. Continence status is closely linked to age, and recruitment of age-matched continent control subjects proved difficult. It is therefore not possible to separate the effects of age and hormonal status on the basis of these preliminary data; our findings could be due to either of these factors, both of which are linked to continence. Also, the supine position induces compression of the glutei, ischiorectal fat, and levator ani muscles. By using different imaging positions and straining tests, these distortions may be minimized but not eliminated (5).

An endovaginal technique may obscure defects because the mass of the endovaginal coil acts as a pessary and supports the anterior vaginal wall. The transverse dimension of the coil that expands the vaginal lumen may tend to minimize the appearance of lateral defects by displacing the vaginal sidewalls laterally (12). In addition, if the coil is connected to a handle, it may act as a lever arm to support and distort the anatomy being studied. The support handle of the coil used in our study was constructed to be as slim as possible to avoid this possibility. However, endovaginal MR imaging provides high-spatial-resolution images that clearly depict the layers of fascia and muscle being studied. It allows a multiplanar capability and is well tolerated by patients.

With use of a specifically designed endovaginal receiver coil, we have shown that GSI patients have a reduced urethral PFV and more than 40% of UL below the inferior border of the pubis in the supine position at rest compared with data in continent premenopausal women. These initial data support the hypothesis that paravaginal fascia plays a key role in the maintenance of continence. However, larger studies with separated effects of aging, parity, and hormonal status would provide further insight into the causes of GSI in women.


   FOOTNOTES
 
2 Current address: Department of Imaging, Hammersmith Hospital, London, England. Back

Abbreviations: GSI = genuine stress incontinence, PFV = paravaginal fascial volume, UL = urethral length

Author contributions: Guarantor of integrity of entire study, N.M.d.S.; study concepts, N.M.d.S., O.J.D.; study design, N.M.d.S., O.J.D., P.D.A.; literature research, A.D.W., N.M.d.S.; clinical studies, N.M.d.S., A.D.W.; experimental studies, D.J.G.; data acquisition, A.D.W., O.J.D.; data analysis/interpretation, O.J.D., N.M.d.S.; statistical analysis, O.J.D., N.M.d.S.; manuscript preparation, N.M.d.S., P.D.A.; manuscript definition of intellectual content, N.M.d.S., O.J.D., P.D.A.; manuscript editing and revision/review, A.D.W., D.J.G.; manuscript final version approval, N.M.d.S., P.D.A.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 

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K. J. Macura, R. R. Genadry, and D. A. Bluemke
MR Imaging of the Female Urethra and Supporting Ligaments in Assessment of Urinary Incontinence: Spectrum of Abnormalities.
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