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Guest Editor: Paddy A. Dewan, MD, FRACS STUDIES OF THE ORIGIN OF SMOOTH AND STRIATED MUSCLES IN THE INTRINSIC URETHRAL SPHINCTER Laurence S. Baskin, MD Sansern Borirakchanyvat, MD ANATOMY OF THE EXTERNAL SPHINCTER Keith W. Kaye, FRCS (SA), FRCS (Edin) Kate E. Creed, BVSc URETHRAL SPHINCTER OF BOYS AS SEEN BY THE PEDIATRIC RADIOLOGIST Robert L Lebowitz, MD URODYNAMIC FUNCTION OF THE EXTERNAL SPHINCTER Kelm Hjalmas, MD, PhD ENDOSCOPIC ANATOMY Paddy A. Dewan, MD, FRACS Editor Richard M. Ehrlich, MD Clinical Professor of Surgery/Urology School of Medicine University of California, Los Angeles Publisher William J. Miller	GUEST EDITOR'S NOTES: The embryology, anatomy, and function of the external urethral sphincter have been studied previously, but not with the degree of sophistication achieved with recent technological advances. The new investigation methods include tissue markers, improved radiology, computer collated urodynamic data, and video recording of urethral endoscopy. Further study is obviously warranted, but the authors have highlighted the important, but less well-known facts that the muscle surrounding the posterior urethra consists of both striated and smooth muscle, the tubular configuration of the external sphincter, and the anatomic relationship of the muscle to the pelvic floor, the prostate, and the verumontanum. The clinical implications of these new perspectives pertain to interpretation of bulbar urethral obstruction and the trans-sphincteric nature of the posterior urethral obstruction which implies that blind disruption of the lesion may damage the sphincter. The challenge remains for the observations of these authors to be confirmed, or refuted by other carefully detailed studies of the anatomy and function of the external sphincter at all stages of development All possible modalities, including others not mentioned here such as 3-D reconstruction of computerized histological sections, should be used to further our understanding of this important structure. Paddy A. Dewan, MD, FRACS
SUBJECT OF CONTROVERSY: EXTERNAL SPHINCTER LAURENCE S. BASKIN, MD Assistant Professor, Pediatric Urology Service, University of California, San Francisco SANSERN BORIRAKCHANYVAT, MD Resident in Urology, University of California, San Francisco Studies on the Origin of Smooth and Striated Muscle Cells in the Intrinsic Urethral Sphincter The embryology of the intrinsic urethral sphincter is poorly understood. The intrinsic urethral sphincter represents a rare anatomical arrangement of striated muscle fibers intimately associated within the wall of a predominantly smooth muscle viscus. Anatomically, the urethral sphincter can be divided into an extrinsic component and an intrinsic component. By definition, the extrinsic urethral sphincter is the striated levator ani muscles that surround the urethra In contrast, the intrinsic urethral sphincter contains both smooth and striated muscle components. The smooth muscle of the urethra is continuous with the smooth muscle of the bladder neck. The origin of the striated component of the intrinsic urethral sphincter, however, is unclear. One intriguing hypothesis which can explain the presence of striated muscle within the intrinsic urethral sphincter involves transdifferentiation of the smooth muscle-like periurethral mesenchyme into striated myotubes. Recent evidence has shown that cells which we previously thought to be terminally differentiated may in fact change their phenotype. The most impressive example of this phenomena exist in the esophagus where smooth muscle cells transdifferentiate to a striated phenotype. An alternative hypothesis may be that the striated component of the urethral sphincter is not from transdifferentiation of smooth muscle cells but results from the lateral migration of precursor stem cells that in turn differentiate into striated myotubes. The striated muscle cells in the intrinsic sphincter are anatomically distinct from other striated muscle groups of the region such as the striated muscle in the extrinsic sphincter. To study the development of the intrinsic urinary sphincter, we performed a careful immunohistochemical analysis of the developing sphincter in the embryonic and postnatal rat Immunohistochemical identification of muscle cell types within the urethra was performed using muscle marker specific monoclonal antibodies. Smooth muscle development within the urethra was studied using anti-a-smooth muscle actin antibody. Striated muscle development was studied using anti-sarcomeric actin antibody and anti-striated myosin heavy chain antibody (MF-20). The development of the intrinsic urethral sphincter in the rat can be detected as early as day 14 of gestation (E14 - Table 1). The urethral sphincter is identified as a oval arrangement of mesenchymal cells. Using hematoxylin and eosin staining, the striated and	Table 1 Expression of Muscle Markers in the Intrinsic Urethral Sphincter of the Rat Age: E14 E16 E18 Day 1 Adult Visible Striated Myotubes - - - + ++ a - Smooth Musche Actin ++ ++ ++ ++ -* a - Striated Sarcomeric Actin - - - + ++ Striated Myosin Heavy Chain - - - - ++ * a-smooth muscle actin is expressed only by the mature smooth muscle of the urethra. The striated muscle component does not express a-smooth muscle actin.   smooth muscle component of the urethra cannot be distinguished at this stage. At E14, E16, and E18, serial sections of the urethra failed to demonstrate a visible striated muscle component within the urethra In contrast the surrounding levator ani muscles can be seen to acquire a striated phenotype as early as day 16 of gestation. When examined with hematoxylin and eosin, striated myotubules were not identified within the urethra until postnatal day 1 (PN1). Immunohistochemical staining using specific smooth and striated muscle marker antibodies demonstrated a specific sequential activation of these markers within the urethral sphincter. The earliest marker expressed in the developing urethral sphincter was a smooth muscle actin which was identified as early as day 14 of gestation and identified through adulthood. In the embryonic and neonatal animals, a smooth muscle actin was detected throughout the developing sphincter mesenchyme. In the adult animal, however, a smooth muscle actin expression was confined to the smooth muscle layer of the urethral sphincter and was not expressed in the striated component. At PN1, the striated component of the intrinsic urethral sphincter is first identified histologically by the presence of striated myotubes. In the neonate, the striated component of the intrinsic urethral sphincter demonstrated immunohistochemical evidence of both smooth and striated muscle markers. The striated myotubes of the developing urethral sphincter in the neonatal animals (PN1) simultaneously expressed a smooth muscle actin and a (sarcomeric) striated muscle actin, although a smooth muscle actin predominates. Striated myosin heavy chain protein, on the other hand, is not expressed in the striated myotubes of the neonate animals, but is strongly expressed in the adult urethral sphincter. Mature smooth and striated muscle components are most readily distinguishable in the adult intrinsic urethral sphincter. Expression of the
smooth muscle actin protein by the striated component of the intrinsic urethral sphincter is lost; a-smooth muscle actin expression is confined to the smooth muscle component of the intrinsic urethral sphincter. Conversely, the mature striated component of the intrinsic urethral sphincter coexpress only the striated muscle markers, a-sarcomeric actin, and striated heavy chain myosin. In conclusion, development of the intrinsic urethral sphincter is characterized by a sequential expression of well-characterized muscle marker proteins. The coexpression of smooth and striated muscle markers by the developing sphincter myotubes suggests that transdifferentiation of smooth to striated muscle occurs in the developing genitourinary tract. This work emphasizes the need for more definitive studies into the embryologic origin of the urethral sphincter. An understanding of the mechanisms that cause smooth and striated muscle differentiation in the urinary tract may lead to new therapeutic strategies for the treatment of urinary incontinence.	descriptions by Henle in 1873 and Holl in 1897 who reported a M. sphincter urethrae and a M. transversus perinei profundus separated from the prostate by a superior aponeurosis. Oelrich, in his classic paper of 1980, clearly demonstrates that there is no such structure as a superior aponeurosis and there is no urogenital diaphragm. We have confirmed this in a recent study. Oelrich also points out that embryologically the primordium of the striated external sphincter is laid down around the urethra, prior to development of the prostate. This primordium extends anteriorly from the perineal membrane (immediately above the corpus spongiosum and bulbospongiosus muscle) to the bladder, and posteriorly from the perineal membrane to the mesonephric ducts (which become the ejaculatory ducts). Subsequently, the prostate, which develops as a posterolateral diverticulum from the urethra, grows into the developing sphincter and causes it to become attenuated in all areas where the prostate develops. At term, because the prostate has not yet surrounded the anterior part of the urethra, the sphincter still extends on its anterior aspect from perineal membrane to bladder. Laterally, the fibers cover the prostate to its posterolateral border, and below the prostate the fibers are sphincteric and completely surround the urethra, being thickest anteriorly. The sphincter reaches the peak of its development between birth and puberty before pubertal growth of the prostate results in destruction of much of the muscle. By puberty, the prostate has developed laterally. It then begins to fuse anteriorly to cover the urethra to varying degrees. As Myers has so well demonstrated, at times the prostate tissue may only fuse anteriorly over the urethra for a fairly short distance resulting in a prostate with a short anterior commissure and a prominent anterior notch, whereas in other individuals the prostate fuses along the length of the urethra anteriorly as far as the prostate extends posteriorly and there is a long anterior commissure and no anterior notch (Figure 1). As the prostate extends anteriorly it grows into the sphincter. A small amount of this may become incorporated into the prostate, where it overlaps the prostate and forms part of the anterior fibromuscular stroma, extending from the sphincter distally to the bladder proximally. Oelrich has also demonstrated that the striated muscle fibers of the sphincter are surrounded by a significant quantity of connective tissue and, as men age, the sphincter atrophies and becomes progressively invaded by extensive vascular and connective tissue, producing an appearance similar to cavernous tissue. It can be seen, therefore, that the final extent and appearance of the striated external sphincter depends
KEITH W. KAYE, FRCS Professor, Urological Research Centre, University of Western Australia, Nedlands KATE E. CREED, BVSC School of Veterinary Studies, Murdoch University, Perth, Western Australia Anatomy and Innervation of the External Urethral Sphincter The success of any surgical procedure depends upon a full understanding of the anatomical structures involved. The external urethral sphincter consists of an inner smooth and an outer striated muscle, surrounding the membranous urethra. The smooth muscle forms a longitudinal layer around the membranous urethra clearly seen on histological studies. The striated muscle, which is thicker anteriorly, is a circumferential cylinder surrounding the smooth muscle and extending from the perineal membrane at the base of the penis to the prostate apex. Unfortunately, even the latest textbooks vary tremendously in their description of the external urethral sphincter, most even neglecting to state that it consists of an inner smooth and outer striated muscle layer. The most accepted concept has been of a "urogenital diaphragm" upon which rests the prostate. The inferior layer of the "diaphragm" is the perineal membrane. This perineal membrane is, in fact, well documented and may clearly be seen during perineal operations which expose the bulb of the penis, such as in total penectomy. The concept of a "superior layer of a urogenital diaphragm," however, arose from
Perineal membrane Figure 1: Striated external urethral sphincter (SEUS). Prostate with short anterior commissure and prominent apical notch. Lateral view. Note SEUS extending to bladder as part of anterior fibromuscular stroma (AFS). MU is the membranous urethra. (Aust NZ J Surg,with permission).
both on the age of the individual and the extent of fusion of the prostate anteriorly over the urethra. The concept of a "urogenital diaphragm" is a myth. There is no such structure and no superior layer of fascia which could be forming such a structure. The term "urogenital diaphragm" should no longer be used. The striated external urethral sphincter is a circumferential cylinder of muscle extending from the perineal membrane above the bulb of the penis and bulbospongiosus muscle to cover all parts of the membranous urethra. Furthermore, in the older adult it extends proximally over the prostate as an attenuated layer being part of the anterior fibromuscular stroma often up to the bladder. The innervation of the external sphincter has also been controversial, many maintaining that the striated component is unique amongst mammalian muscles, having both a somatic and an autonomic supply. We have demonstrated recently that stimulation of the pudendal nerve in dogs produces contraction of the striated component that is completely blocked by curare, and that the pudendal nerve has branches which run into the muscle from its penile end, similar to the human. Additionally, stimulation of the pelvic nerve (parasympathetic) produces a slow pressure rise in the dog postprostatic urethra typical of smooth muscle. We also found branches from the pelvic nerve entering the striated muscle but passing through it to the underlying smooth muscle. Thus the striated component of the external sphincter, certainly in the dog, has a somatic motor innervation from the pudendal nerve only, whereas the smooth muscle has an autonomic supply from the pelvic nerve. There is accumulating evidence that the nerve bundles in the human which originate from the pelvic plexus (combined sympathetic and parasympathetic nervous systems which run in the groove between prostate and rectum to provide for penile erection) also send branches to the smooth muscle component of the external sphincter. This is from findings that when the neurovascular bundles are removed with radical	prostatectomy for prostate cancer there is a reduced rate of urinary continence compared to when the bundles are preserved. Both the striated muscle component, with its slow twitch fibers, and the smooth muscle play roles in urinary continence. It would appear the longitudinal smooth muscle shortens the membranous urethra, thus permitting the more substantial circumferential striated muscle to exert a greater compressive effect Levator ani contains some fast-twitch fibers which supplement the external sphincter under stress conditions. In summary, it is now apparent that the external urethral sphincter consists of an inner longitudinal smooth muscle layer and an outer circumferential striated muscle layer extending from the perineal membrane to the prostate apex and continuing over the anterior aspect of the prostate as part of the anterior fibromuscular stroma. In addition, in keeping with innervation of other muscles in the body, it appears as if the striated component is innervated by the somatic pudendal nerve and the smooth muscle component by autonomic nerves, probably from branches of the nerves which pass to the penis for erection. ROBERT L. LEBOWITZ, MD Professor of Radiology, Boston Childrens" Hospital, Boston Urethral Sphincter in Boys as Seen by the Pediatric Radiologist The urinary continence "mechanism" in the boy, as seen by the pediatric radiologist, consists of two components: the bladder neck (also called the internal sphincter) and the urethral sphincter (also called the external sphincter or simply the sphincter). Both the bladder neck and the sphincter are closed at rest in normal boys, providing continence of urine. During voiding, the bladder neck and the sphincter open synchronously, one immediately after the other, the
	resulting pressure in the posterior urethra above the closed sphincter results in the characteristic findings: the posterior urethra becomes dilated above the closed sphincter, the body of the bladder becomes trabeculated, and there may begin to be reflux into the prostatic ducts, the ejaculatory ducts, or the prostatic utricle (Figure 2). These findings worsen with time and if the degree of dyssynergy increases. In the boy with posterior urethral obstruction, the obstruction cannot be seen on VCUG unless the sphincter is open (and the boy is voiding), since valves emanate from the distal end of the verumonantum, which is well below the cephalad.
	KELM HJALMAS, MD, PhD Associate Professor of Pediatric Surgery, University of Gothenberg, Sweden Urodynamic Function of the External Sphincter In urodynamic studies of external sphincter behavior, we are privileged in not having to consider in depth the much discussed issues of anatomy and innervation. We are only concerned with the dynamic, that is, hydrodynamic effects of a structure located somewhere around the urethral flow channel, a structure able to close or open more or less intermittently, in harmony with or antagonizing, respectively, the actions of the detrusor muscle pump. Urodynamics cannot contribute much knowledge about the composition, location, and innervation of the external sphincter, but it is satisfied by studying its clinically important effects on bladder behavior and urinary flow. Some initial statements need to be made about urodynamics of the external sphincter in children, especially that: • Urodynamic data about sphincter behavior often are misleading; and, • Noninvasive investigation with uroflow most often yields the best information about sphincter function in children. The background for these statements is the unique innerration of the lower urinary tract, the only interior organ system in the body to which all three major nerve systems converge: the two autonomic and the somatic. Somatovisceral integration is therefore essential for normal continence and evacuation of the lower urinary tract, including proper sphincter action. The bladder sends signals to the sensory cortex about increasing tension in its wall. When the bladder reaches its functional capacity, a desire to void is elicited in the cortex, leading to a series of conscious actions such as searching out a proper place to void, and arranging the clothing appropriately for the act of micturition. The final conscious decision is to start the voiding by ordering the sphincter to relax (and, to
Figure 2: Diagramatic representation of the external sphincter as seen radiologically. bladder neck first (During ejaculation, the bladder neck remains closed while the sphincter opens so that the ejaculate can pass out the urethra and not back into the bladder.) Pediatric radiologists, while performing fluoroscopically monitored voiding cystourethrography (VCUG), can see this normal synchronous opening of first the bladder neck and then the sphincter on almost every study. Yet, like other things regularly observed (the daily sunrise, for example), the phenomenon often begins to be taken for granted. At times, we might even fail to appreciate the remarkable nature of the event. Retrograde urethrography (RUG) shows the effect of the closed sphincter on the urethra. During VCUG in the normal boy, the bladder neck is closed during filling. As voiding begins, the bladder neck opens and the sphincter remains closed for a very short time, sometimes less than a second (Figure 2). When the sphincter opens, a notch can often be seen on the anterior surface of the urethra, just opposite the middle of the verumonantum, called the intermuscular incisura (Figure 2, arrow). It marks the cephalad extent of the now-open sphincter. On RUG, since the boy is not voiding during the study, the end of the column of contrast material shows the caudal end of the sphincter. Where the closed sphincter constricts the lumen, the urethra appears "steepled" or pointed (Figure 2). This tapered region has been called the cone of the bulbous urethra. By combining the two images, one from VCUG and one from RUG, we can determine both the cephalad and the caudal limits of the sphincter, and hence its length. In the boy with bladder-sphincter dyssynergy (from meylomeningocele, for example), as the bladder contracts to expel urine, the bladder neck opens but the sphincter does not relax appropriately. The
SUBJECT OF CONTROVERSY: EXTERNAL SPHINCTER some extent, ordering the detrusor to contract) which will allow urine to enter the posterior urethra, eliciting the micturition reflex. When the viscerosomatic coordination functions properly, the micturition reflex will sustain detrusor contraction and sphincter relaxation, respectively, until the bladder is emptied completely. After voiding, the reverse will be true. The strong cortical control of the lower urinary tract is both the enemy and the friend of urodynamic investigations. In the mature and cooperative patient, bladder function can be scrutinized by interviewing the patient about bladder sensation at different degrees of filling and asking the patient to stop micturition in midlfow, etc. The child between two and six or seven years of age, however, is not readily motivated to participate in an invasive examination. Information on why it is necessary to go through with the investigation is received by the child with suspicion, which sometimes is well founded. Signals of danger and imminent discomfort reach the child's cortex from the more primitive thalamic parts of the brain, creating tension and anxiety. Even in a child with perfectly normal bladder and urethra function, this state of mind creates these exact signs of dysfunction: hyperactivity of both detrusor and sphincter and imperfect coordination between the two. The presence of a transurethral catheter may increase the risk of overdiagnosing bladder and urethral dysfunction, since contact between the catheter and the urethral mucosa may set up a segmental medullary reflect over the sacral micturition center, also creating detrusor/sphincter hyperactivity and inco-ordination. It is quite obvious, therefore, that a completely non-invasive procedure holds the best chance to reveal true dysfunction of the external sphincter in a child. So, what is true sphincter dysfunction? Sphincter contraction during an unstable detrusor contraction during bladder filling is not a pathological phenomenon; it is a physiological response to an increase in bladder pressure, aimed at preserving continence. By contrast, sphincter contraction is pathological when it counteracts evacuation of urine from the bladder. Unstable sphincter relaxation during bladder filling is also pathological since it gives rise to incontinence. The latter condition, unstable urethra, is, however, much debated and very difficult to demonstrate. Once the child becomes confident that urofiow investigation just means voiding in a pot, the noninvasive urofiow/residual urine measurement is the superior way to look at sphincter behaviour in a child. The normal, coordinated flow curve is even and bell-shaped (Figure 3). The micturition most often does not leave any residual urine, meaning less than 5 ml in a child. By contrast, dysfunctional voiding with sphincter activity during micturition results in a ragged curve shape, the so-called staccato or irregular curve
	Figure 4: Dysfunctional voiding with sphincter activity during micturition results in a ragged curve shape, the so-called staccato or irregular curve.
	(Figure 4). There is often more than 5 ml of residual left behind because the voiding was partly obstructed. Even if the flow curve does not give direct evidence of sphincter hyperactivity, the sharp dips in the flow curve cannot be explained in any other way, provided the child was in a reasonably happy mood during the investigation. In order to sort out minor irregularities in the curve shape, it is our practice only to accept curve indentations deeper than the square root of the maximum flow rate (in mis) as signs of rebellious sphincter contraction. By contrast, the fractionated flow curve (Figure 5) is not a sign of sphincter hyperactivity. Rather, it denotes an insufficient detrusor contraction assisted by straining with the abdominal muscles. The external sphincter during cystometry. Compared to urofiow, cystometry puts much greater demands on the laboratory to handle the child with patience and tenderness. Even so, the presence of the catheter in the bladder gives a much increased risk for artifacts. We, therefore, never perform cystometry without a preceding uroflow. Signs of sphincter hyperactivity in the cystometrogram, such as a sudden steep rise of detrusor pressure, should be looked on as artifacts if there were normal curve shapes during urofiow.
Fractionated	structural infravesical obstruction. However, the present state of urodynamics does not allow us to identify smooth muscle dyscoordination with any precision. Regarding the bladder neck, it is our opinion that this structure does not contribute much to the sphincter function. A true sphincter is able both to relax and to contract by its own muscle action. The bladder neck seems to open passively through the "suspender action" of the detrusor contraction during micturition, and only contracts during ejaculation. Conclusion. We want to issue a warning against evaluating urethral sphincter action in children based on the results of cystometry, sphincer EMG or urethral pressure profile. The good news here is that the non-invasive, repeated uroflow in a confident, relaxed child gives reliable and reproducible information about the functional status of that particular child's sphincter. The prerequisite is that the uroflow examination be performed by personnel who like children, who understand their special needs, and who are able to perform the examination with tenderness in the child's own place.
Figure 5: The fractionated flow curve is not a sign of sphincter hyperactivity, but an insufficient detrusor contraction assisted by straining with the abdominal muscles. Sphincter EMG. With the exception of a few complicated neuropathic disorders, sphincter EMG has only a limited use in pediatric urodynamics. We routinely use perianal cutaneous electrodes during cystometry, and sometimes also at uroflow, but we are seldom any the wiser after collating these data. In rare instances, however, the cutaneous sphincter EMG may be able to discriminate structural urethral obstruction from that rebellious sphincter contraction. A reliable sphincter EMG requires the use of percutaneously placed electrodes, but this technique is impossible in the small child since the correct placement of the electrode tip demands that a patient be awake and cooperative during the insertion. In a child with neuorgenic bladder, leak point pressure gives a better estimate of sphincter activity, ie, the degree of dyssynergia rather than the notoriously unreliable cutaneous electrode. Urethral pressure profile. What has been said already about artifacts induced by a catheter residing in the urethra of a child is true also for examination of urethral pressure whether performed with a fluid-filled system or with microtip transducers. We have not received much relevant clinical information from doing pressure profiles. The exception is the odd patient with an artificial urinary sphincter where the urethral pressure profile may tell us whether the periurethral cuff exercises adequate compressive pressure on the urethra. Hyperactivity of the smooth muscle sphincter? So far, we have been talking only about the urodynamics of the striated sphincter. It is perfectly possible, indeed probable, that the smooth muscle sphincter also may show the features of hyperactivity and uncoordination. The contraction speed of smooth muscle dyscoordination would not be evidence of sudden changes of urinary flow rate. Rather, a smooth muscle sphincter dysfunction might manifest itself as a long waiting time before micturition can be initiated, or as a restricted flow rate throughout voiding, imitating a
	PADDY A. DEWAN, MD, FRACS Associate Professor, Urology Unit, Royal Children's Hospital, Parkville, Victoria, Australia Endoscopic Anatomy Keith Kaye has highlighted the findings from detailed dissections of the urethral sphincter at various ages, concluding that the sphincter is a continuous tube of muscle from the bladder to the perineal membrane, with a relative condensation of fibers caused by the growth of the prostate gland. It has been suggested that the continuous tube of striated muscle forms a "muscle complex", not too dissimilar to the muscle complex associated with the lower bowel. The predominance of the striated muscle fibers in the anterior wall of the urethra, just distal to the verumontanum, may represent the most physiologically active component of the external sphincter as seen endoscopically. This would fit with the impression from the published findings of Bradford Young and from 87 video recorded endoscopies of normal male urethras I have performed over a five-year period. The urethra was considered normal if the sphincter could be seen to come to rest at the lower edge of the verumontanum when the bladder was empty. This positioning of the sphincter could obviously not be confirmed historically, but it concurs with the endoscopic descriptions of others. The greater degree of activity of the muscle fibers located just beyond the prostate may be similar to the lower end sphincter in the esophagus, and explain why the sphincter has been considered to be a ring-like structure endoscopically. Work by Hendren in 1971 demonstrated a spectrum of obstruction of the posterior urethra which supported
SUBJECT OF CONTROVERSY: EXTERNAL SPHINCTER Young's classification. He studied the relationship between the obstruction and the urethral sphincter, concluding that the urethral sphincter is the more distal, which is a crenated ring-like structure. However, from the endoscopic procedures videorecorded over a five-year period in 42 boys, part of the sphincter was seen to be proximal to the obstructing membrane. Thirty-eight of the boys had a cystogram prior to their endoscopy. Twenty-two of them with a congenital obstructive posterior urethral membrane (COPUM) were truly obstructive, 14 were less obstructive and six were minor incidental membranes, but were more than prominent folds from the verumontanum. In 36 cases, the cranial extent of the external sphincter was identified proximal to the posterior urethral membrane with good correlation with the radiologic cystograms. Hendren's conclusion that the sphincter was below the obstruction may be due to the distal end of the sphincter being prominent in many of his 182 cases. This would be regarded as Cobb's collar or Moormann's ring by others and it would appear to represent the distal end of the external sphincter which is located at the level of the bulbar urethra. Over the same five-year period mentioned above, 66 boys were found to have narrowing in the bulbar with either a muscular or a fibrous appearance (Table 2). Congenital narrowing of the bulbar urethra has not often been discussed in the literature, possibly because insertion of the cystoscope, while visualizing the urethra, will often show the presence of a ring narrowing of the bulbar urethra which has had little documentation and therefore is little understood. Also, there has not previously been attempts to correlate endoscopic video findings with radiological images. In my patients such a narrowing was found in only 66 of the boys in whom there was an adequate recording of the bulbar urethra. Forty-six of these were thought to be muscular in nature (Table 2); it would seem that narrowing in the bulbar urethra is often congenital and, when muscular, represents the distal end of the external sphincter complex. Stephens, Gibbons and associates, and Currarino suggested, from cystogram studies, that the muscular, variable constriction of the bulb is due to contraction of the separate striated muscle of the bulbospongiosus contraction. The endoscopic view shows the constriction to be circumferential and both endoscopic and radiologic views in Moormann's series, plus the late age of presentation, fit with the constriction being at the lower end of the external sphincter. Patients with a congenital narrowing in the bulbar urethra have often been grouped with boys who have traumatic or iatrogenic strictures, leading Harshman and colleagues to conclude that the term congenital stricture should be avoided. Nevertheless, congenital narrowing has been seen in our study and in the six cases reported by Currarino and Stephens where	Table 2 Bulbar Urethral Abnormalities Grouped by Type and Degree Muscular Membranous     Unk     Total Minimal 15 0               12        27 Moderate 19 5 0         24 Severe 2 3 0          5 Total 46 8               12        66
	cystograms similar to our cases were shown. The presence of a membranous lesion in our case where the diagnosis of hydronephrosis was made prenatally, and the young age of most of the boys, supports the notion that these lesions are congenital. This is also suggested in other studies where young boys have presented with upper tract changes with an obstructing membrane in the bulbar urethra. In contrast, Cobb and associates thought the lesion could not be muscle since the 26 children he recorded had a narrowing which was not affected by succinylcholine. The boys and older men who present have a normal stream, a completly obstructed urethra on urethrogram, but an easily traversed, crenated region in the bulbar urethra are the extreme end of the spectrum of spasm at the lower end of the external sphincter complex, of which there were two in 46 with a muscular lesion. These findings would fit with the older age of Moormann's patients and the finding of similar changes in a father and son, and in brothers.
	EDITOR'S COMMENTS: This is a unique issue that, once more, demonstrates the versatility of Dialogues, which is a solid tribute to our Guest Editors and their coauthors. Australia's Paddy Dewan has assembled an outstanding cast of contributors who give our readers a host of important observations and clinical experiences. Our hat's off to Paddy Dewan and his coauthors for providing us with this treasure of up-to-date perspectives. Richard M. Ehrlich, MD Opinions expressed in this publication are the sole responsibility of the individuals named and do not necessarily reflect the opinions of the editorial board or the publisher and members of this organization. Copyright © 1997 by William J. Miller Associates, Inc. All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying recording or by any information retrieval system, without written permission from the publisher.