0022-534 7/90 /1433-0563$02.00 /0 Vol. 143, March

THE JOURNAL OF UROLOGY

Printed in U.S.A.

Copyright© 1990 by AMERICAN UROLOGICAL ASSOCIATlON, INC.

Urological Neurology and Urodynamics THE ANATOMY OF STRESS INCONTINENCE: MAGNETIC RESONANCE IMAGING OF THE FEMALE BLADDER NECK AND URETHRA CARL KLUTKE, JACOB GOLOMB, ZORAN BARBARIC

AND

SHLOMO RAZ

From the Departments of Surgery (Division of Urology) and Radiology, UCLA School of Medicine, Los Angeles, California

ABSTRACT

Clinical, urodynamic, radiological and endoscopic evaluations as well as operative results on more than 800 cases of stress incontinence treated at our medical center have led to a better understanding of the pathophysiology of female stress incontinence. We attempt to correlate these physiological concepts with information obtained from magnetic resonance images of the paraurethral and bladder neck areas in patients with known stress incontinence and normal controls. All magnetic resonance images were compared to cadaver step sections of the female pelvis. Normal controls without stress incontinence were used to define normal anatomy by magnetic resonance imaging. Etiology of incontinence was divided into either intrinsic urethral damage or anatomical malposition of an intact sphincteric unit. Our findings not only provide valuable support to basic concepts of the pathophysiology of stress incontinence but also help to establish normal findings of female paraurethral and bladder neck anatomy as seen by magnetic resonance imaging. (J. Ural., 143: 563-566, 1990) Magnetic resonance imaging rapidly is becoming a major diagnostic tool in the assessment of internal pathological conditions. Its greatest value presently in the evaluation of the pelvis has been visualization and accurate staging of tumors. Since the noninvasive, nonionizing, multi-planer imaging capabilities offer distinct advantages over computerized tomography (CT) and since it has greater accuracy over ultrasound in the detection of discrete structures, it rapidly is becoming an accepted modality for the evaluation and detection of varied pelvic pathological conditions, such as prostatic tumor extension and undescended testis. 1 We have been interested in the use of this new modality towards a better understanding of female stress incontinence. Stress urinary incontinence, or the involuntary loss of urine through the intact urethra without a detrusor contraction and which is a social or hygienic problem to the patient, is the result of a deficient urinary control system. Failure of this system results in intra -abdominal pressure exceeding the resistance produced by the bladder outlet closure mechanism. Normally, anatomical support of the bladder neck and proximal urethra allows for through transmission of intra-abdominal pressure increases to this area of continence, and together with an intrinsically intact urethra with its coapting mucosa! surface leakage does not occur. Leakage can occur as a result of failure at either or both of these 2 points. The anatomical basis of these pathophysiological concepts is an area of confusion and controversy, and yet only through a clear conceptual understanding of the anatomy involved can rational treatment be given. Our purpose is to relieve some of the confusion surrounding the anatomy of continence by analyzing magnetic resonance images of the bladder neck and proximal urethral area, and comparing them to pelvic step sections to determine those structures important to normal continence as well as stress urinary loss. Accepted for publication September 12, 1989. 563

MATERIALS AND METHODS

Axial step-sections of the female pelvis were used in combination with magnetic resonance images of the bladder neck and periurethral area. Step-sections were taken of the pelvis of a human female cadaver with no known history of urinary incontinence. These were performed with a heavy duty cryomicrotome at an operating temperature of -20C. 2 A total of 50 patients 30 to 73 years old was studied with magnetic resonance imaging. Five patients were without symptoms of urinary incontinence and 45 were diagnosed with genuine stress incontinence. The diagnostic criteria for genuine stress incontinence included history, physical examination, and radiographic and urodynamic findings consistent with standard criteria. 3 Patients with genuine stress incontinence were categorized further into those with incontinence due to anatomical descent of an intact sphincter unit and to an intrinsically damaged urethra.4 Thus, 42 patients could be classified as having anatomical and 3 as having intrinsic damage incontinence. Magnetic resonance imaging was performed with a 0.3 Tesla permanent magnet with a belt type surface coil placed around the patient at the level of the symphysis pubis. Axial contiguous images (7 mm.) were obtained with T2-weighted spin-echo sequence (repetition time 2,000 msec., echo delay time 85 msec.) on a 256 X 256 matrix and 20 cm. field of view. On this imaging sequence muscles and connective fibrous tissues appear to be hypointense (darker) compared to surrounding high signal intensity fat and bone marrow. RESULTS

Beginning our examinations with the cadaver step-sections (fig. 1, B), we could follow the bony pelvic scaffolding to the pelvic musculature that attaches to it and supports the pelvic viscera. The obturator internis is visualized clearly lateral to the viscera, and the levator muscle is seen drawing its support from the so-called arcuate line of obturator fascia. The levator from these origins extends down, beneath and around the pelvic

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FIG. 1. A, axial magnetic resonance image at level of bladder neck in well supported continent woman shows urethropelvic ligaments (arrows,

UPL) supporting bladder neck. B, corresponding step-section at same level shows urethropelvic ligaments attaching to levator (arrows) at level of arcus tendineous.

viscera (urethra, vagina and rectum) as it unites with the fibers from the opposite side. Thus, the levator fibers hold the intrapelvic organs like a hammock, providing support as well as stabilization during increases in intra-abdominal pressure. Further examination reveals direct medial extensions off the levator to the bladder neck and urethra. The fibers extending onto the bladder neck and proximal urethra are seen to extend from the levator at the point of origin from the obturator internis. We refer to these extensions originating at the levator muscle

from the arcuate line to the bladder neck and proximal urethra as the urethropelvic ligaments. Magnetic resonance images of the well supported female pelvis without stress incontinence corroborate these medial extensions off the levator to the area of the proximal urethra and bladder neck. Figure 1, A exemplifies the features seen in patients studied without stress incontinence. The magnetic resonance spin coefficient allows us to characterize these structures as musculofascial in content. No other structures can be seen on magnetic resonance images

Pubic syrnphysis

Levator sling

FIG. 2. Axial magnetic resonance section at level of bladder neck in patient with genuine stress urinary incontinence. Bladder neck descent can be seen by increased distance between it and pubic symphysis. UPL, urethropelvic ligaments.

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m.

Levotor sling

FIG. 3. Axial magnetic resonance image at level of proximal urethra in patient who presented after numerous unsuccessful operations for severe stress incontinence. Arrow shows deficient area in surrounding smooth muscle capsule. Note high retropubic position of urethra resulting from previous bladder neck suspensions.

attaching to the bladder neck with as much compositional strength. Note the normal H configuration of the vagina in cross-section as the anterior vaginal wall conforms to and reflects the well supported bladder neck and proximal urethral area. Characteristics of good bladder neck support seen on magnetic resonance imaging in an overview of our continent patients studied included tight, nearly horizontal urethropelvic ligaments on an axial scan, a bladder neck positioned close to the pubic symphysis and a vaginal lumen with a widened H appearance in cross-section. Figure 2, A is a preoperative magnetic resonance image taken at the level of the bladder neck and proximal urethra, with typical features seen in patients with stress urinary incontinence. In this image at the level of the bladder neck and proximal urethra, the urethropelvic ligaments are seen to extend downward (dorsally) in an oblique course to the main body of the levator sling-no longer the discrete horizontally extending structures seen in the previous images. Furthermore, anterior vaginal wall prolapse may be inferred by the inverted U configuration of the vagina, When attention is turned to the urethra itself, some important information may be elucidated further on magnetic resonance images. The urethra consists largely of a richly vascular a coat of smooth muscle, 5 fibroelastic sponge surrounded Built up of loosely woven connective tissue scattered throughout by tiny smooth muscle bundles and an elaborate vascular plexus, the submucosa creates the thick round (whiter) structure seen on magnetic resonance images. The surrounding smooth muscle coat is in sharp contrast with its blacker (hypointense) consistency on the image. Figure 3, A shows a pathological condition of this structure, A patient with a history of multiple anterior vaginal wall and periurethral operations presented with severe stress incontinence but with a clinically and radiologically well supported bladder neck and proximal urethra, Magnetic resonance imaging at the level of the proximal urethra near the bladder neck revealed the surrounding smooth muscular coat to be deficient in its most dorsal aspect where it abuts the vagina, consistent with a history and symptomatology of intrinsic urethral damage secondary to surgical trauma. The patient subsequently underwent a vaginal sling procedure with complete cure of the stress incontinence. DISCUSSION

We can summarize our study of urethral and bladder neck support by highlighting the presence of the direct musculo-

fascia! attachments originating from the levator muscle at the tendinous arc to the bladder neck and proximal urethra. We have referred to these structures as the urethropelvic ligaments and they can be visualized clearly on magnetic resonance images at the level of the bladder neck and proximal urethra. Characterized as musculofascial according to the spin coefficient of magnetic resonance, these urethropelvic ligaments in effect attach the bladder neck and proximal urethra not only to the levator muscle, thereby elevating and compressing the urethra during reflex levator contraction such as at times of sudden increases in intra-abdominal pressure, but to the pelvic wall via the obturator internis allowing for stability and support of the proximal urethra and bladder neck. Correlating these anatomical findings with our current concept of stress incontinence pathophysiology, relaxation of these ligaments as with the generalized pelvic relaxation after childbirth and aging would allow for posterior and downward rotation of the proximal urethra and bladder neck, placing these structures out of the realm of effective intra-abdominal pressure transmission and potentiating incontinence, The various types of bladder neck suspension procedures all share the objective of replacement of the bladder neck and proximal urethra into a high fixed position. As one gains a better view of the supporting structures it becomes clear that what structures are resuspended more importantly, where they are on the eventual outcome. VI/hen the dangers of obstruction and 1acroe'en urethral damage are present, When too distal to the bladder neck and urethra insufficient suspension of the continence mechanism occurs and no improvement in symptoms will be achieved. The Raz bladder neck suspension 6 breaks the lateral attachment of the endopelvic fascia to provide not only mobility of the anterior vaginal wall but also proper access to the urethropelvic ligament. Fundamental to this suspension is the precise placement of anchoring sutures so as to include the vaginal wall and urethropelvic ligament as lateral as possible to achieve strong support of the bladder neck without interference with the normal mobility of the urethra. Of no less importance to an understanding of stress urinary incontinence is knowledge of the intrinsic urethral component. The loosely woven connective tissue of the submucosa with its elaborate plexus of vascular spaces creates the so-called washer effect for the continence mechanism. Functionally, the surrounding smooth muscle coat maintains this mechanism by directing submucosal expansile pressures inward towards the

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mucosa. This highly efficient mucosal seal is a major contributor to the closure mechanism of the urethra and, as such, an important area of evaluation in the patient with stress urinary loss. Multiple operations, trauma and radiation can affect the ability to achieve a perfect urethral seal and when this mechanism is lost stress incontinence of intrinsic damage results. Simple bladder neck and proximal urethral suspension in this case will be insufficient to achieve continence (indeed it may be entirely unnecessary) and treatment must be aimed at providing the missing element (urethral coaptation and compression). Magnetic resonance imaging appears to be the first cross-sectional imaging modality able to demonstrate visually and clearly, and evaluate this important area of continence. The advantage over CT and ultrasound lies in its ability to provide good soft tissue differentiation, and allow the examiner to distinguish muscular sheath from submucosa and evaluate the integrity of both structures. With a relatively small, selected patient population studied, our magnetic resonance imaging results certainly must still be viewed as preliminary and prospective studies are in order. Further experience with this modality may confirm or refute our findings and further define its diagnostic usefulness outside the research setting. Presently, magnetic resonance imaging of the periurethral and bladder neck areas cannot be considered a practical aid in the evaluation of female incontinence. However, our anatomical findings coupled with our pathophysiological understanding helps us to divide genuine stress urinary incontinence into that due to anatomical malposition of an intact sphincteric unit on one hand and incontinence secondary to insufficiency of the urethral closing mechanism or intrinsic urethral damage on the other. While we believe the goal of an

operation for anatomical incontinence is to elevate and support the bladder neck in a high fixed retropubic position by resuspension of the urethropelvic ligaments, the goal of an operation in patients with intrinsic urethral damage should be to provide coaptation and compression of the urethra to restore its sealing function. Of course, female stress continence depends upon numerous other factors, including the proper hormonal milieu, the proper reflex contracture of pelvic muscles at the time of suddenly increased intra-abdominal pressure and a host of other even less well understood aspects. Although anatomy is not the only factor involved in stress incontinence, its importance to the urologist lies in its being the only surgically correctable factor. Thus, only through a better anatomical understanding of the structures involved with continence can the proper diagnosis be made and proper surgical treatment be rendered. REFERENCES

1. Fritzsche, P. J. and Smith, D.: MRI's role in male pelvis includes

staging of tumors. Diag. Imag., 10: 114, 1988. 2. Holliday, J., Saxon, R., Lufkin, R. B., Rauschning, W., Reicher, M., Bassett, L., Hanafee, W., Barbaric, Z., Sarti, D. and Glenn, W., Jr.: Anatomic correlations of magnetic resonance images with cadaver cryosections. Radiographies, 5: 887, 1985. 3. Massey, A. and Abrams, P.: Urodynamics of the female lower urinary tract. Urol. Clin. N. Amer., 12: 231, 1985. 4. Raz, S., Siegel, A. L., Short, J. L. and Snyder, J. A.: Vaginal wall sling. J. Urol., 141: 43, 1989. 5. Huisman, A. B.: Aspects on the anatomy of the female urethra with special relation to urinary continence. Contrib. Gynec. Obst., 10: 1, 1983. 6. Raz, S.: Modified bladder neck suspension for female stress incontinence. Urology, 17: 82, 1981.

The anatomy of stress incontinence: magnetic resonance imaging of the female bladder neck and urethra.

Clinical, urodynamic, radiological and endoscopic evaluations as well as operative results on more than 800 cases of stress incontinence treated at ou...
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