Some Aspects of Striated Urethral Sphincter Structure and Function

Some Aspects of Striated Urethral Sphincter Structure and Function

0022-534 7/94/1526-2321$03.00/0 Vol. 152, 2321-2323, December 1994 THE JOURNAL OF UROLOGY Copyright © 1994 by AMERICAN Printed in U.SA. UROLOGICAL...

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0022-534 7/94/1526-2321$03.00/0 Vol. 152, 2321-2323, December 1994

THE JOURNAL OF UROLOGY

Copyright © 1994 by AMERICAN

Printed in U.SA.

UROLOGICAL AssoCIATION, INC.

Urological Neurology and Urodynamics SOME ASPECTS OF STRIATED URETHRAL SPHINCTER STRUCTURE AND FUNCTION JOHN B. NANNINGA From the Department of Urology, Northwestern University Medical School, Chicago, Illinois

ABSTRACT

During the last 2 decades various routes of investigation have enhanced our knowledge of the striated urethral sphincter. Anatomic and neurophysiological studies as well as clinical evaluation in the form of urodynamic studies have demonstrated the components of the sphincter and its function. This information has provided the urologist with greater understanding of problems related to striated sphincter function. KEY WORDS:

urethra, muscles, urinary incontinence

It is an honor to have the opportunity to participate in the Festschrift for Doctor Grayhack. As a former resident and current department member, I have gained immeasurably from his stimulating mind and many contributions to urology. In the last few decades understanding the urethral sphincter mechanism has increased as techniques for investigation have revealed some of the mysteries of urinary continence. Some of the discoveries, advances and reappraisals of striated sphincter anatomy and function are presented in this review. Hopefully, the information presented will stimulate the reader to ponder the behavior of the striated component of the urinary sphincter mechanism and contribute to the treatment of urinary incontinence. During the last 2 decades various routes of investigation, including clinical observations, have enhanced our knowledge of the striated urethral sphincter. The increased use of radical prostatectomy has heightened interest in the exact location and function of this muscle complex. The increased recognition of urinary incontinence in the aging population in both sexes has also been an impetus to our understanding of the mechanisms of urinary continence and the role played by the striated muscle component of the urethral sphincter. In male and female subjects the 2 entities that make up the striated muscle of the sphincter mechanism are the striated urethral sphincter and the levator ani, which provide support and some degree of compressive action. 1- 3 STRUCTURE

the growth of the prostate. 1 • 5 During puberty the growth of the prostate displaces the sphincter distally and incorporates part of it anteriorly. The sphincter shows varying amounts of striated muscle fibers anteriorly and laterally near the junction of the apex of the prostate and membranous urethra. 1 • 5 • 6 Until the membraneous urethra is reached, the sphincter tends to have a horseshoe appearance. 6 There is no clear-cut plane or division between the prostate and urethral sphincter for striated muscle fibers are present within the substance of the prostate. 1 • 5 • 7 As the urethra leaves the apex of the prostate, it travels caudally to and through the perinea! membrane where it is surrounded by striated urethral sphincter fibers and medial fibers of the levator ani musculature. The levator is maintained in proximity to the prostate and membranous urethra by its medial fascia. 6 Structurally, the levator would seem to offer lateral support as well as some degree of compression during active contraction. Myers has indicated that the compressor function of the levator is not homologous with the female compressor urethrae. 6 The striated sphincter has been shown to be composed largely of slow twitch fibers (type I). 8 Such muscle is capable of maintaining tension for a long period. The levator ani, specifically the pubococcygeal component, elevates the urethra so as to compress the urethra when contracted. This muscle is composed of a mixture of slow and fast twitch fibers (type II), and is capable of producing rapid compression of the urethra when the urinary stream is voluntarily interrupted or when sudden elevation in abdominal pressure occurs. 4 • 8 • 9 Thus, the levator actively assists the urethral striated sphincter in responding to sudden intravesical pressure elevation that could cause incontinence. Normally, continence requires an intact internal sphincter (bladder neck) as well as normal positioning of the bladder neck and urethra. 3 The striated sphincter fibers appear to be unique in several ways. 8 • 10 The urethral sphincter and the levator, which is in close proximity to the urethra, demonstrate fibers that are unusually small. No spindles have been found in the striated sphincter and the muscle lacks the septal divisions usually found in other striated muscles of the body. 10

In the female subject striated sphincter fibers surround the urethra over the middle third. This muscle has been termed the sphincter urethrae, or simply urethral sphincter. 2 Moving distally and blending with the sphincter urethrae are striated fibers of the urethrovaginal component of the sphincter. These fibers do not surround the urethra but pass laterally along the urethra and then posteriorly around the vagina. Finally, there is a compressor urethrae, which crosses anterior to the urethra in conjunction with the previously mentioned urethrovaginal component, and inserts in the ischiopubic rami. 2 This muscle serves to compress the urethra anteriorly and can pull the urethral meatus caudally and INNERVATION inferiorly. Taken collectively, these striated muscles comThe motor neurons giving off nerves to the sphincter are prise as much as 80% of the luminal length of the urethra. 3 • 4 located in the area of the sacral cord referred to as Onufs The anatomy of the striated sphincter in the male subject nucleus. 11 By gross anatomical study and histological methis associated with the presence of the prostate and altered by ods, the ventral horn of 82 and S3 levels appears to be 2321

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STRIATED URETHRAL SPHINCTER STRUCTURE AND FUNCTION

the origin of the pudendal nerve component traveling to the striated sphincter. 12 In careful dissection of the pelvic plexus a few somatic fibers from the anterior root have been found to run close to the autonomic pelvic plexus, which has been interpreted as suggesting that the innervation of the striated sphincter may be somatic and autonomic. Of interest are the findings that diseases affecting the skeletal muscles, such as amyotrophic lateral sclerosis, spare the sphincter, while diseases involving the autonomic nervous system may produce abnormalities in Onufs nucleus. 10 • 13 An exception would be certain distal autonomic neuropathies that appear to spare the urethral sphincter. 14 Studies on animals indicate that the sacral nucleus of the striated sphincter and the bulbocavernosus muscle is sexually dimorphic. 15 Male subjects have a greater number of motor neurons because of a greater bulk of target muscles. The dimorphism is due to the influence of androgens during development. 16 It is interesting to speculate that some loss of sphincter control in the elderly woman may relate to relatively fewer motor neurons for the striated sphincter as well as changes associated with aging. Higher centers that control the sphincter are located in the pons and cerebral cortex. Specifically, the lateral part of the pontine tegmentum sends fibers to the nucleus of Onuf. 17- 19 This center is responsible for the resting tone as well as the reflex relaxation that occurs in the sphincter during voiding. In the brain there are areas that when stimulated contract the sphincter or inhibit the pontine detrusor center. Experimentally, the medial aspect of the motor cortex contains cells that cause contraction of the sphincter on stimulation. 20 Laboratory studies have also shown that an area of the amygdala will cause a contraction of the sphincter. 21 In the human damage to the medial aspect of the premotor cortex causes decreased bladder capacity, suggesting loss of a bladder control center. 22 Thus, the supraspinal centers allow coordination of the sphincter with bladder expulsive function as well as voluntary contraction of the sphincter. Pharmacological studies have shown that the sphincter complex is affected by drugs that alter the sympathetic nervous system. a-Adrenergic blocking drugs decrease the urethral pressure peak in the region of the striated sphincter, although the effect may be documented all along the urethra. 23- 25 Based on various studies, the effect of norepinephrine on sphincter activity would seem to be central rather than peripheral. 26 • 27 Clinically, the smooth muscle of the bladder neck and proximal urethra as well as the striated sphincter appear to be influenced by sympathetic agents, the result of sympathetic block being to reduce striated muscle activity. EVALUATION

There are many techniques with which the urologist can evaluate striated sphincter function. Whether the patient can retain urine and start and stop the urinary stream comprises a gross estimation of the contractile ability of the sphincter. However, it should be recalled that the striated sphincter is only 1 component of the continence mechanism. The bladder neck and supporting structures also contribute to the prevention of incontinence. Evaluation of the striated urethral sphincter is often guided by the disease process that has initiated the need for evaluation. Incontinence after radical prostatectomy focuses attention on the bladder as well as the striated sphincter. Assuming that detrusor instability has been ruled out by cystometry, then the evaluation centers on the distal sphincter mechanism. Endoscopy provides a visual appearance of the anastomotic site of the bladder neck and the membranous urethra containing striated muscle. The operator can visualize whether the sphincter moves and closes with voluntary contraction. Radiological evaluation offers an effective method of documenting closure of the sphincter. 6 • 28 • 29 Oblique or lateral

films with contrast material in the bladder and urethra will provide an estimate as to the length of the membranous urethra and whether the urethra coapts. Hutch measured the length of the vesicourethral junction in patients after radical prostatectomy and found the average length in continent patients to be 2.8 cm. (range 2.3 to 3.4), while the average length in incontinent patients was 1.2 cm. (range 0. 7 to 1.6). 28 Myers indicated that a urethral length of 1.5 cm. or less could be considered a short urethral package and, while not definitely predisposing to incontinence, does suggest that steps taken at surgery to gain maximum length of the urethra when resecting the apex of the prostate may well improve chances of continence postoperatively. 6 In female patients radiological evaluation either with standard x-ray or fluoroscopic visualization provides a valuable tool with which to diagnose closure, movement and position of the bladder and urethra. 30 - 32 When the diagnosis of stress incontinence seems likely, the lateral radiograph will demonstrate the relationship of the urethra to the bladder. Asking the patient to bear down and taking a film will define the effectiveness of the sphincter mechanism and its supports in maintaining continence. Fluoroscopy allows the operator to see the actual movement of the bladder and urethra during coughing or straining. Combining fluoroscopy with the measurement of detrusor pressure and sphincter electromyography (video urodynamics) provides the best means of defining detrusor function along with visualizing the sphincter mechanism so as to arrive at a diagnosis. With this information treatment can be directed at the exact cause of the bladder and/or urethral dysfunction. Recently, magnetic resonance imaging has been used in the diagnosis of incontinence. 33 • 34 It has been effective in defining the relationship of the supporting mechanism to the bladder and urethra, and showing loss of levator muscle composition. This technique has also demonstrated loss of the intrinsic, smooth muscle component of the sphincter mechanism and aided in planning surgical correction ofincontinence. 33 When neurological causes may have a role in abnormal voiding or incontinence, electromyography of the sphincter will aid in defining function in the striated muscle and whether sphincter function is coordinated with bladder function. 35· 36 As a screening study, surface electrodes are suitable for noting any changes in sphincter activity occurring with bladder pressure changes. 37 If denervation is suspected, needle electrodes will detect the typical changes of denervation, such as fibrillation potentials and positive sharp waves. 36 • 38 In the female subject the needle (coaxial or bipolar) is placed alongside the urethra to a depth of 1 to 1.5 cm., noting the appearance of action potentials on the oscilloscope. In the male subject the needle is guided up to the membranous urethra. The apex of the prostate serves as a convenient target for the tip of the needle. The oscilloscope shows the typical pattern when striated muscle fibers are encountered. If stimulation equipment is available a so-called sacral latency can be performed. This study involves stimulating the glans penis or clitoris and noting the appearance of action potentials on the screen. The normal latency is about 35 msec. 39 Delay in the appearance of the signal and/or abnormal action potentials indicates an abnormality in the sacral cord or in the peripheral nerves. 38 • 39 The urethral pressure profile is a study that has been used to document pressure along the urethra. The purpose is to document any deficiencies along the urethral closure mechanism and try to correlate these findings with the clinical status. Perfusion and withdrawal of the catheter is 1 method by which to document various pressure changes. 23 • 40 The technique is not easily applied to situations when the patient changes position in an effort to show leakage, coughs or strains. Consequently, pressure sensitive tip catheters have been developed, which can be moved proximally or distally and which allow the patient to perform maneuvers that du-

STRIATED URETHRAL SPHINCTER STRUCTURE AND FUNCTION

plicate conditions causing incontinence. 29 • 41 • 42 Any pressure changes can be documented and areas of deficiency noted. Difficulty in interpretation occurs because movement artifact or torsion of the catheter and excessive wall contact may cause abnormally high pressures. Also, it is difficult to define any 1 number above or below which incontinence does or does not occur. Often the x-ray demonstration provides a more easily interpretable study with which to document urethral sphincter abnormalities. 31 • 32 In summary, the striated sphincter serves to provide a constant retentive function as well as capability of quick contraction so as to prevent leakage of urine when abdominal pressure increases suddenly. A variety of tests are available to evaluate sphincter function. Much remains to be elucidated about the striated sphincter function in terms of innervation, anatomical support and aging. Also, new knowledge of sphincter physiology may point the way to drugs that will strengthen the sphincter or provide appropriate relaxation to facilitate emptying. REFERENCES 1. Oelrich, T. M.: The striated urethral sphincter muscle in the male. Amer. J. Anat., 158: 229, 1980. 2. Oelrich, T. M.: The striated urogenital sphincter muscle in the female. Anat. Rec., 205: 223, 1983. 3. DeLancey, J. 0. L.: Functional anatomy of the female pelvis. In: Female Urology. Edited by E. D. Kursh and E. J. McGuire. Philadelphia: J.B. Lippincott Co., chapt. 1, pp. 3-16, 1994. 4. DeLancey, J. 0. L.: Anatomy and physiology of urinary incontinence. Clin. Obst. Gynec., 33: 298, 1990. 5. Beneventi, F. and Marshall, V. F.: Some studies of urinary incontinence in men. J. Urol., 75: 273, 1956. 6. Myers, R. P.: Male urethral sphincteric anatomy and radical prostatectomy. Urol. Clin. N. Amer., 18: 211, 1991. 7. Nanninga, J., Rosen, J. and O'Conor, V. J., Jr.: Experience with transurethral external sphincterotomy in patients with spinal cord injury. J. Urol., 112: 72, 1974. 8. Gosling, J., Dixon, J., Critchley, H. and Thompson, S.: A comparative study of the human external sphincter and periurethral levator ani muscle. Brit. J. Urol., 53: 35, 1981. 9. Schroder, H. D. and Reske-Nielsen, E.: Fiber type in the striated urethral and anal sphincters. Acta Neuropath., 60: 278, 1983. 10. Schroder, H. D.: Anatomical and pathoanatomical studies on the spinal efferent systems innervating pelvic structures. J. Autonom. Nerv. Syst., 14: 22, 1985. 11. Onuf, B.: On the arrangement and function of the cell groups of the sacral region of the spinal cord in man. Arch. Neurol. Psychopath., 3: 387, 1901. 12. Junemann, K.-P., Schmidt, R., Melchior, H. and Tanagho, E.: Neuroanatomy and clinical significance of the external urethral sphincter. Urol. Int., 42: 132, 1987. 13. Gibson, S. J., Polak, J., Katagiri, T., Su, H., Weller, R., Brownell, D., Holland, S., Hughes, J., Kikuyama, S., Ball, J., Bloom, S., Steiner, T., de Belleroche, J. and Rose, F. C.: A comparison of the distributions of eight peptides in spinal cord from normal controls and cases of motor neuron disease with special reference to Onufs nucleus. Brain Res., 474: 255, 1988. 14. Kirby, R., Fowler, C., Gosling, J. and Bannister, R.: Bladder dysfunction in distal autonomic neuropathy of acute onset. J. Neurol. Neurosurg. Psychiat., 48: 762, 1985. 15. Breedlove, S. M. and Arnold, A. P.: Hormone accumulation in a sexually dimorphic motor nucleus of the rat spinal cord. Science, 210: 564, 1980. 16. Goldstein, L. and Sengelaub, D.: Timing and duration of dihydrotestosterone treatment affect the development of motorneuron number and morphology in a sexually dimorphic rat spinal nucleus. J. Comp. Neurol., 326: 147, 1992. 17. Holstege, G., Griffiths, D., de Wall, H. and Dalm, E.: Anatomical and physiological observations on supraspinal control of bladder and urethral sphincter muscles in the cat. J. Comp. Neurol., 250: 449, 1986. 18. de Groat, W. C. and Ryall, R.: Reflexes to sacral preganglionic parasympathetic neurons concerned with micturition in the cat. J. Physiol., 200: 87, 1969. 19. Noto, H., Roppolo, J., Steers, W. and de Groat, W. C.: Excitatory

20. 21.

22. 23. 24. 25.

26.

27.

28. 29. 30. 31. 32. 33. 34.

35. 36.

37.

38. 39. 40. 41. 42.

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and inhibitory influences on bladder activity elicited by electrical stimulation of the pontine micturition center in the rat. Brain Res., 492: 99, 1989. Fukuda, H. and Koga, T.: Stimulation of three areas of the primary motor cortex interrupts micturition in dogs. J. Autonom. Nerv. Syst., 38: 177, 1992. Koyama, K.: Effects of amygdaloid and olfactory tubercle stimulation on efferent activities of the vesical branch of the pelvic nerve and the urethral branch of the pudenda! nerve in dogs. Urol. Int., suppl., 47: 23, 1991. Andrew, J. and Nathan, P.: Lesions of the anterior frontal lobes and disturbances of micturition and defaecation. Brain, 87: 233, 1964. Donker, P. J., Ivanovici, F. and Noach, E.: Analysis of the urethral pressure profile by means of electromyography and the administration of drugs. Brit. J. Urol., 44: 180, 1972. Nordling, J., Meyhoff, H. and Hald, T.: Sympatholytic effect on striated urethral sphincter. Scand. J. Urol. Nephrol., 15: 173, 1981. Thind, P., Lose, G., Colstrup, H., and Andersson, K.-E.: The effect of a-adrenocepter stimulation and blockade on the static urethral sphincter function in healthy females. Scand. J. Urol. Nephrol., 26: 219, 1992. Gajewski, J., Downie, J. and Awad, S.: Experimental evidence for a central nervous system site of action in the effect of alpha-adrenergic blockers on the external urinary sphincter. J. Urol., 133: 403, 1984. Rajaofetra, N., Passaglia, J.-G., Marlier, L., Poulat, P., Pellas, F., Sandillon, F., Verschuere, B., Gouy, D., Geffard, M. and Privat, A.: Serotoninergic, noradrenergic and peptidergic innervation of Onufs nucleus of normal and transected spinal cords of baboons (papio papio). J. Comp. Neurol., 318: 1, 1992. Hutch, J.: Anatomy and Physiology of the Bladder, Trigone and Urethra. New York: Appleton-Century-Crofts, pp. 128-129 and 168-169, 1972. Presti, J., Schmidt, R., Narayan, P., Carroll, P. and Tanagho, E.: Pathophysiology of urinary incontinence after radical prostatectomy. J. Urol., 143: 975, 1990. Stamey, T., Schaeffer, A. and Condy, M.: Clinical and roentgenographic evaluation of endoscopic suspension of the vesical neck for urinary incontinence. Surg., Gynec. & Obst., 140: 355, 1975. McGuire, E. and Woodside, J.: Diagnostic advantages of fluoroscopic monitoring during urodynamic evaluation. J. Urol., 125: 830, 1981. Blaivas, J.: Videourodynamics. In: Clinical Neuro-Urology. Edited by R. J. Krane and M. R. Siroky. Boston: Little, Brown & Co., chapt. 14, pp. 265-273, 1991. Klutke, C., Golomb, J., Barbaric, Z. and Raz, S.: The anatomy of stress incontinence: magnetic resonance imaging of the female bladder neck and urethra. J. Urol., 143: 563, 1990. Kirschner-Hermanns, R., Wein, B., Niehaus, S., Schaeffer, W. and Jakse, G.: The contribution of magnetic resonance imaging of the pelvic floor to the understanding of urinary incontinence. Brit. J. Urol., 72: 715, 1993. Diokno, A., Koff, S. and Bender, L.: Periurethral striated muscle activity in neurogenic bladder dysfunction. J. Urol., 112: 743, 1974. Chantraine, A.: EMG examination of the anal and urethral sphincters. In: New Developments in Electromyography and Clinical Neurophysiology. Edited by J. E. Desmedt. Basel: Karger, vol. 2, pp. 421-432, 1973. Siroky, M.: Electromyography of the perineal striated muscles. In: Clinical Neuro-Urology. Edited by R. J. Krane and M. B. Siroky. Boston: Little, Brown & Co., chapt. 12, pp. 245-247, 1991. Ertekin, C., Reel, F., Mutlu, R. and Kerkuku, I.: Bulbocavernosus reflex in patients with conus medularis and cauda equina lesions. J. Neurol. Sci., 41: 175, 1979. Krane, R. and Siroky, M.: Studies on sacral evoked potentials. J. Urol., 124: 872, 1980. Abrams, P., Martin, S. and Griffiths, D. J.: The measurement and interpretation of urethral pressure obtained by the method of Brown and Wickham. Brit. J. Urol., 50: 33, 1978. Constantinou, C.: Resting and stress urethral pressures as a clinical guide to the mechanism of continence in the female patient. Urol. Clin. N. Amer., 12: 247, 1985. Hilton, P. and Stanton, S.: Urethral pressure measurement by microtransducer. Brit. J. Obst. Gynaec., 90: 919, 1983.