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ORIGINAL RESEARCH

Sonographic Evaluation of the Bladder Neck in Continent and Stress-Incontinent Women

SCHAER, GABRIEL N. MD; PERUCCHINI, DANIELE MD; MUNZ, EVA MD; PESCHERS, URSULA MD; KOECHLI, OSSI R. MD; DELANCEY, JOHN O. L. MD

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Although disagreement exists about the clinical importance of funneling in the proximal urethra, to the best of our knowledge, the depth and diameter of funneling during known increases in abdominal pressure have not been measured in stress-continent and -incontinent women. The present study was done to evaluate the feasibility of quantifying diameter of vesical neck dilation during Valsalva and cough maneuvers and to determine to what depth contrast medium can be seen through the urethra in a group of continent and stress-incontinent women.

Materials and Methods

We studied 58 women, 30 of whom had stress urinary incontinence, and 28 of whom were healthy volunteers who had no symptoms of urinary incontinence and were stress continent on urodynamic evaluation. The mean (± standard deviation [SD]) age was 43 ± 14 years (stress urinary incontinence = 50 ± 14 years, continent = 36 ± 9 years). Among incontinent women, two were nulliparous and 28 parous, compared with 15 nulliparous and 13 parous controls. Ultrasound studies are done currently for each woman with incontinence symptoms referred to our urodynamic unit. Each woman diagnosed with urodynamically proven stress incontinence from June to August 1996 was included. Continent women were recruited from our outpatient clinic after completing questionnaires and showing continence during stress cough tests with bladder volumes of at least 250 mL (verified by ultrasound measurement). The study was approved by the local ethical committee, and informed consent was given by the participating women. Women were excluded if they had previous incontinence surgery, congenital anomalies of the lower urinary tract, or causes of urinary incontinence other than stress.

Full urodynamic assessment was done on all women, including history, clinical examination, pad weighing and cough test, water-filling cystometry, and urethral pressure profile at rest and during coughing. Evaluations were done according to recommendations of the International Continence Society.1 Pressure measurements were intraurethral, intravesical, and intrarectal pressure recordings, recorded on a SEDIA SE-8 urodynamic machine (Sedia AG, Givisiez, Switzerland). After history and clinical examination, water-filling cystometry was performed with patients supine, using a no. 10 French Gaeltec microtip transducer catheter (CTU-L2; Gaeltec Ltd., Dunvegan, Scotland). Abdominal pressure was measured with an intrarectal balloon catheter.

Each patient's bladder was filled to capacity with isotonic saline solution at room temperature at an infusion rate of 60 mL/minute. Bladder volume was reduced to 300 mL by catheterization, and urethral pressure profiles at rest and during coughing were measured. The intraurethral pressure catheter was removed, and cough stress tests were done supine and standing. The presence or absence of leakage was recorded. Afterwards, a standard pad-weighing test was conducted. Any increase in pad weight of more than 1 g was significant.

The lower urinary tract in the vesical neck region was assessed by perineal ultrasound with ultrasound contrast medium (Echovist-300; Schering AG, Berlin, Germany), injected transurethrally into the bladder by a single-use catheter, as reported.2,3 Perineal ultrasound was done on upright patients with a 5-MHz curved linear array transducer (Aloka SSD 2000; Aloka Ltd., Tokyo, Japan) placed lightly against the vulva in a sagittal orientation to view the bladder, bladder neck, urethra, and pubis. Incontinent patients were told to push or cough as hard as necessary to produce urinary leakage, whereas the continent subjects were asked to push or cough as hard as possible. The ultrasound video signal was digitized by a frame grabber card and displayed on a computer screen. Intrarectal pressure was superimposed on the ultrasound picture with synchronous data on abdominal pressure and ultrasound signals. These pictures were videotaped for analysis by slow-motion playback. Bladder neck position at rest, during Valsalva, coughing, and pelvic floor contraction was measured with the x, y coordinate system, based on the pubic bone (Figure 1).4 Bladder neck movement was calculated using the formula:

Figure 1
Figure 1:
Measurement of bladder neck movement (bottom right) and width (w) and depth (d) of urethral dilation (bottom left) during coughing and Valsalva. Location was measured relative to a coordinate system based on the longitudinal axis of the pubic bone, and movement was calculated as a vector between the resting, Valsalva, or coughing positions.

where x1 and y1 represent coordinates at rest, and x2 and y2 during coughing or Valsalva.5

Measurements of urethral dilation were made by marking the depth to which the V-shaped wedge of contrast extended along the urethra (Figures 1 and 2). The level of internal urinary meatus was marked at the anterior urethrovesical angle. A line perpendicular to the axis of the urethra from the vertex of the anterior vesical angle to the posterior urethral wall was drawn and measured to assess urethral dilation. The distance from this line and the tip of the V were measured to determine depth.

Figure 2
Figure 2:
Sonographic appearance of bladder neck dilation during Valsalva in a continent (left) and stress urinary incontinent woman (right). The ultrasound contrast medium (UCM) precipitates at the bladder base and bladder neck. The bladder neck was dilated in both cases (upper left corner). Although the incontinent woman had leakage of contrast medium along the entire urethra, only the funnel of the bladder neck was measured. B = urinary bladder; S = symphysis pubis; * = internal urethral meatus; + = external urethral meatus.

Abdominal pressures of the two groups were compared using the Mann-Whitney test.

Results

Abdominal pressure increases measured during Valsalva or cough were not statistically significantly different between the incontinent group and controls. Valsalva pressure (±SD) in the incontinent group was 56 ± 28 cm H2O, and in controls, 43 ± 16 cm H2O. Cough pressure in incontinent women was 85 ± 31 cm H2O, and in controls, 72 ± 20 cm H2O.

Figures 3 (Valsalva) and 4 (coughing) show intrarectal pressures, depth and width of urethral dilation, and bladder neck descent for each of the 58 subjects. Data were arranged by continent or incontinent group, and increasing abdominal pressure values for each group of parity. During Valsalva, all the incontinent and 12 continent women had contrast enter the urethra. During coughing, dilation was visible in 29 incontinent and six continent women. One incontinent woman showed dilation only while performing Valsalva and not during coughing. In the continent group, nulliparous women did not present dilation during Valsalva or coughing.

Figure 3
Figure 3:
Intra-abdominal pressure increase, depth and width of urethral dilation, and bladder neck descent during Valsalva for each of the 30 incontinent and 28 continent subjects. The sorting order depends on increasing intrarectal pressure values and whether the woman belongs to the continent or incontinent group.
Figure 4
Figure 4:
Intra-abdominal pressure increase, depth and width of urethral dilation, and bladder neck descent during coughing for each of the 30 incontinent and 28 continent subjects. The sorting order depends on increasing intrarectal pressure values and whether the woman belongs to the continent or incontinent group.

Bladder neck descent was seen in both groups.

Discussion

Contrast media placed in the urinary bladder can, under certain circumstances, enter the proximal urethra.6 We described a technique that quantifies the depth and diameter of contrast medium visible in the urethra during measured abdominal pressure conditions.

The internal urinary meatus must open for urinary incontinence to occur. The fact that it is pushed open by increases in abdominal pressure does not always mean that urine escapes from the distal urethra. Our findings agree with those of Versi et al,6 who performed video-urethrocystography in climacteric patients and found bladder neck funneling in 51% of the continent women. It is possible for abdominal pressure to open the internal urinary meatus while the distal urethra is held closed. That also was the case in some continent women in our study. In those women, the depth of urethral dilation indicated where along the urethra the pressure was high enough to keep it closed. The range of depth in continent women (between 0 and 19 mm) indicated that continence can be maintained by different structures within the urethra, and that urethral closure is a dynamic process along the urethra.

Anatomic and histologic studies found the different structures contributing to urethral closure, such as the detrusor muscle sling around the proximal urethra, the longitudinal and circular smooth muscle fibers, the striated urethral sphincter, the urethrovaginal sphincter, and the compressor urethrae.7 The first two-thirds of the urethra lie where the urethral support system is most effective.8 Along the urethra, different muscle structures contribute to urethral closure. The integrity and function of those different structures are shown in the findings of our perineal ultrasound assessment. Morphometric studies of striated urethral muscles found that their volume relative to connective tissue decreases with age.9 Histologic observations of striated urethral muscles found striated muscle loss at the bladder neck and along the dorsal wall of the urethra with advancing age.10 Those results might indicate that urethral dilation without incontinence is an abnormal finding, ie, of damage to the striated urethral sphincter, which is compensated for by the distal urethral muscles.

The comparison of urethral dilation between nulliparous and parous continent women provides new information. The fact that no nulliparous, but 12 (Valsalva) and six (coughing) of the 13 parous women presented urethral dilation is a further indication that giving birth might cause pelvic floor defects, and that the structure most vulnerable to damage is the proximal urethra. In the continent women with proximal dilation, the distal urethra was able to compensate for the proximal defect by keeping the urethra closed distally. Because the numbers of parous and nulliparous groups within the continent women were quite small, interpretation of the results has to be made cautiously. However, the positive association between our ultrasound findings and those of urethral anatomy and histology encourages further testing of such hypotheses.

In addition to information on bladder neck dilation, ultrasound provides information on bladder neck movements caused by coughing or Valsalva. Results showed that a certain amount of bladder neck mobility is physiologic and probably helpful in terms of voiding. Those results agreed with the findings of Ala-Ketola,11 which showed significant overlap in urethral mobility between continent and incontinent women.

There are several considerations in determining how to quantify the depth and diameter of urethral dilation. Consistently visible landmarks and measuring strategies that apply to the variety of shapes require a sensible balance between practicability and anatomic purity. The anterior margin of the internal meatus is consistently visible, whereas the posterior margin often flattens out and is not recognizable. Therefore, we chose the anterior margin to determine location of the internal meatus and constructed a line perpendicular to the axis rather than trying to estimate the true posterior position of the internal meatus.

The level at which continence occurs has been controversial. Some authors believe that continence is determined at the internal urinary meatus, whereas others maintain that structures along the urethra contribute to continence. Those favoring the vesical neck as the level of continence point out that in normal women, urine does not enter the urethra during coughing, that the distal urethra can be excised without incontinence, and that urethral support operations cure incontinence without changing urethral function. On the other hand, incontinence occurred in most women undergoing vul-vectomy with excision of the distal urethra,12 and many continent women have urine visible in the urethra.6

Our study defined three groups of women, the first, continent at the vesical neck; the second, with urine traversing the bladder neck during increases in abdominal pressure, but stopping further down the urethral; and the third, with urine traversing the bladder neck and escaping the external meatus. Those observations raised the questions: 1) What structural or functional capabilities of vesical neck or urethral supports differ between groups 1 and 2? 2) Between groups 2 and 3, what structural or functional capabilities determine whether urine is stopped mid-urethra or escapes distally? The key to answering these questions is comparison of observations of continent and incontinent women determination of anatomic structures responsible for those differences. The technique described here, coupled with function assessments and anatomic data, done in a large-scale study of incontinent women, should help get these answers.

References

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© 1999 The American College of Obstetricians and Gynecologists