Primary non-refluxing megaureters

Journal of Pediatric Urology (2005) 1, 409e417

EDUCATION ARTICLE

Primary non-refluxing megaureters E. Merlini*, P. Spina Department of Paediatric Surgery, ‘‘Ospedale Maggiore della Carita`’’ Hospital, Corso Mazzini 18, 28100 Novara, Italy Received 26 February 2005; accepted 18 April 2005 Available online 5 July 2005

KEYWORDS Megaureter; Hydroureter; Obstructive uropathy

Abstract Megaureters may be primary or secondary, and the dilatation may be due to obstruction or reflux, or both or neither. The cause of primary obstructed megaureter is the aperistaltic and narrowed pre-vesical portion of the ureter. The inner sheath of the terminal ureter generally shows a reduced amount of longitudinal smooth muscle bundles and an increased amount of collagen. Primary non-refluxing megaureters represent 23% of all prenatal diagnoses of hydronephrosis. They are more common in males and on the left side, and in 25% are bilateral. In older children they may become symptomatic. The diagnostic work up should include an ultrasound, a micturating cystourethrogram and an isotopic renogram. Most primary megaureters regress spontaneously or remain stable without compromising renal function, but 10e25% require surgery because of a progressive reduction in renal function or increasing dilatation, or because they become symptomatic. The basic principles of surgical repair include: resection of the obstructing segment, reduction in size of the dilated ureter, and re-implantation into the bladder using an anti-reflux technique. ª 2005 Journal of Pediatric Urology Company. Published by Elsevier Ltd. All rights reserved.

Introduction and classification The word megaureter is a descriptive term for ‘dilated or larger than normal ureter’ and it is synonymous with ‘wide ureter’, ‘hydroureter’ and ‘megaloureter’.

* Corresponding author. Tel.: C39 3213733497; fax: C39 3213733997. E-mail address: [email protected] (E. Merlini).

Cussen in 1971 [1] and Hellstrom et al. in 1986 [2] demonstrated that in normal children the ureteral diameter rarely exceeds 5 mm, and therefore a larger ureter can be defined as a ‘megaureter’. In 1977 Smith [34] proposed a classification of megaureters that was largely accepted and later modified by King in 1980 [3] who added the ‘refluxing and obstructed megaureter’. Megaureters are divided into:  non-obstructed/non-refluxing,  obstructed,

1477-5131/$30 ª 2005 Journal of Pediatric Urology Company. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.jpurol.2005.04.007

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 refluxing, and  obstructed and refluxing. Each group can be further subdivided into primary and secondary megaureters. The causes of secondary megaureters are:     

infection, diabetes insipidus, external obstruction, neuropathic bladder, and posterior urethral valves.

Here we will be discussing about primary obstructed and non-obstructed megaureters.

Primary non-refluxing megaureters Demographics A primary non-refluxing megaureter is a common cause of hydronephrosis among neonates: it is identified in approximately 23% of neonates with prenatally detected dilatation of the urinary tract. Primary non-refluxing megaureter is four times more common in males than in females. The left ureter is affected 1.6e4.5 times more frequently than the right, and in approximately 25% of cases both sides are involved. Children presenting before the age of 1 year are more likely to be bilaterally affected than older children. The kidney contralateral to a primary non-refluxing megaureter is either absent or dysplastic in 10e15% of patients. The condition is not hereditary, even when more cases in the same family have been described [4].

Primary non-obstructed megaureters Most primary megaureters detected in neonates fall into this category, where there is neither demonstrable obstruction at the vesico-ureteral junction (VUJ) nor reflux, but nevertheless the extravesical ureter is dilated. This phenomenon is not completely understood and different explanations have been proposed. In the third trimester foetal urine production is four to six times greater than after delivery. This phenomenon is due to differences in vascular resistance, glomerular filtration rate (GFR) and concentrating ability. This large amount of fluid may challenge the immature VUJ and dilate the ureter, in much the same way as is observed in diabetes insipidus. The foetal and neonatal ureters are also more compliant due to

the difference in the deposition of collagen III, elastin and matrix proteins. The most widely accepted hypothesis for non-obstructive, temporary dilatation of the neonatal ureter is that the VUJ may suffer from a delay in establishing valid peristalsis due to a transitory delay in maturation. Also, persistent foetal ureteral folds may account for transient mild obstructive uropathy. Primary non-obstructive, non-refluxing megaureters generally return to normal in the first 2 years of life.

Primary obstructive megaureters Aetiology and pathology The cause of a primary obstructive megaureter (POM) is still a matter of speculation. There is general agreement that in most cases there is no true narrowing at the VUJ, but a functional obstruction arising from an aperistaltic, juxtavesical segment 0.5e4 cm long, that is unable to transport urine at an acceptable rate. Endoscopically, the obstructed ureteral orifice has a normal appearance and inserts in a normal position on the trigone in the majority of cases. Occasionally, a true stenosis of the distal ureter can be demonstrated, while in other cases the ureter may terminate ectopically in a more distal position. Swenson in 1952 [5] hypothesized that a POM could be caused by the absence of intramural nerve ganglia as in Hirschsprung’s disease, but accurate histological examination of specimens taken from the distal, obstructing ureter showed a normal distribution of ganglia. Several authors have focused their attention on the histology of the aperistaltic, distal, ureteral segment. In 1970, Tanagho et al. [6] found that in their autopsy cases the obstructing effect was due to a circular rather than longitudinal orientation of muscle fibres, and the degree of obstruction was related to the number of circular fibres. These authors also pointed out that the terminal ureter is the last portion to develop its muscular coat that is primarily circular in orientation. Gregoir and Debled [7] found contrary evidence in their study of 30 primary megaureters. Functionally obstructing segments were divided into four categories: in 60% of cases dense collagen infiltration in the terminal 3e4 cm of distal ureter was found; in the remaining 40% circular muscle hypertrophy of the ureteral orifice, fibroepithelial embryonal dysplasia and complete embryonal dysplasia were described. McLaughlin et al. in 1973 [8] reported an accurate histological analysis of the obstructing segments in

Primary non-refluxing megaureters 32 patients. The findings were divided into four categories: normal ureters in five cases, abnormal orientation of muscle bundles in two cases, mural fibrosis with little or no muscle fibres in three cases, and in 22 specimens muscle atrophy with wide separation of muscle bundles that appeared to be pulled apart by fibrosis. This last finding was commonly observed in the distal ureters resected in the present study (Figs. 1 and 2). Electron microscopy has further elucidated the pathologic process of primary megaureter. Hanna et al. [9] described: ‘‘excessive collagen fibres between and around muscle cells and a group of compromised muscle cells proximal to a collagenous segment. These findings are responsible for the functional discontinuity and the indistensibility of the pathologic areas’’. Segmental changes of muscle cells in the adynamic segment were also highlighted by Nicotina et al. [10], who reported atrophy of the inner longitudinal muscle that conducts the peristaltic wave and hypertrophy of the outer circular layer which causes obstruction. Other investigators have confirmed these findings, which are limited to the distal obstructing portion of the ureter. Recently, Lee and co-workers [11] have analysed the amount and subtypes of collagen in primary megaureter and found no difference in normal controls. The collagen was predominantly type I and the tissue matrix ratio of collagen to muscle was not statistically different from normal controls. Dixon and associates [12] showed another cause of POM. They reported on three cases of primary obstructed ectopic megaureters, where they found that the distal ureter was encircled by a dense coat of smooth muscle, separated from the normal, longitudinally oriented, ureteral muscle bundles

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Figure 2 Transverse section of the aperistaltic portion of a POM. Immunohistochemical staining for actin filaments shows sparse and reduced smooth muscle bundles in the inner muscular sheath of the ureteral wall.

by loose connective tissue. This muscle layer showed dense noradrenergic innervation that might cause it to constrict inappropriately, impeding urinary flow and, ultimately, leading to the development of megaureter. Nicotina et al. [10] hypothesize on the possible pathogenic role of transforming growth factor (TGF b) which has been shown to effect maturation of smooth muscle cells. TGF b delays muscle cell differentiation and is detectable in the foetal ureter from 11 to 21 weeks, but not thereafter. These authors found TGF b in resected specimens of the VUJ of children with obstructed ureters who were under the age of 2 years, but not in older children operated on for non-obstructive reasons. They postulate that the progressive decrease of TGF b in the first 2 years may correlate with the spontaneous improvement of primary megaureter. Regardless of the cause, the aperistaltic segment prevents urine draining normally into the bladder, and urine collects cranial to the aperistaltic segment leading to ureteric dilatation. The dilated ureter is a larger and more compliant reservoir than the pelvis and, consequently, the pressure inside the dilated ureter is less elevated than that recordable in the pelvis in the case of pelvi-ureteral junction (PUJ) obstruction; therefore, it would be less likely for the dilatation caused by VUJ obstruction to transmit damaging pressure to the kidneys.

Clinical presentation Figure 1 Transverse view of the aperistaltic portion of a POM (stain: Mallory Azan ! 100). The abundant collagen (stained green) separates the smooth muscular bundles (purple red) that are reduced in number.

Currently, about half of the megaureters diagnosed are asymptomatic and identified on a prenatal ultrasound. Foetal sonography has increased the number of megaureters that are identified in

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utero. Brown and co-workers [13] have shown that before the prenatal ultrasound era clinically significant megaureters accounted for 10% of all hydronephroses, preceded by PUJ obstructions (22%), posterior urethral valves (19%) and ureteroceles (14%). Since the widespread use of foetal ultrasound, megaureters are reported to occur in 23% of neonates with prenatal hydroureteronephrosis, which makes VUJ obstruction the second most common obstructive uropathy after PUJ, which occurs in approximately 41%. The presenting postnatal symptoms of megaureters are febrile urinary tract symptoms which may be provoked by urinary stasis or stone disease.

Diagnosis Ultrasound is the initial procedure performed in a child suspected of having a urinary tract abnormality. The dilated ureter can be traced from the renal pelvis to its entry into the bladder; it is often tortuous and peristaltic, and antiperistaltic waves are frequently seen. The ureter is visualized behind the bladder as it terminates with a large, bulbous ending changing abruptly to the thin aperistaltic segment (Fig. 3). In transverse scans the dilated ureter appears as a round transonic image behind the bladder (Fig. 4). Echography can also help in differential diagnosis as it may show the ureter ending ectopically or in a ureterocele. The pelvis and calyces can be hydronephrotic with cortical thinning, but usually the ureter is more prominently dilated than the calyces and pelvis. Sometimes dilatation is limited to the distal

Figure 3 Ultrasound: longitudinal scan of the bladder. Behind the bladder the bulbous distal portion of a megaureter is visible (arrow).

Figure 4 Ultrasound: transverse scan of the bladder. Behind the bladder the dilated ureter is seen as a round transonic image (arrow).

third of the ureter and the remaining ureter and pelvis are normal. Ultrasound is also a useful tool for the follow up of megaureters treated expectantly, because it can measure precisely the dimensions of the retrovesical ureter and pelvis. After a megaureter is identified, the second investigation should be a voiding cystourethrogram (VCUG), which helps to distinguish between a non-refluxing and refluxing megaureter. This procedure is also invaluable in showing a possible cause of secondary megaureter such as posterior urethral valves or a neuropathic bladder, which may be strongly suspected from the views of the bladder seen on a VCUG. Once it is clear that we are dealing with a primary non-refluxing megaureter, the next and most difficult step is to diagnose the presence of obstruction. In the last 20 years it has become clear that urinary tract dilatation does not necessarily mean obstruction. A practical definition of partial urinary tract obstruction was given by Koff in 1987 [14] who stated: ‘‘.obstruction is any restriction to urinary flow that, if left untreated, will damage kidney function.’’. This definition clearly implies that there is no method that can ‘measure’ directly the degree of obstruction, and that can reliably assess the existence of a significant impairment of the urinary flow before it has caused damage to renal function. Of course, waiting until permanent damage has occurred to the kidney is not an acceptable procedure. Therefore, all efforts have been focused on obtaining a reliable method of diagnosing partial obstruction to urinary flow before it damages the kidney. An intravenous pyelogram (IVP) is

Primary non-refluxing megaureters not a good diagnostic test as it gives poor information about the existence of a restriction of urinary flow, it does not provide any measurement of renal function, especially in neonates and infants and when renal function is decreased, and anatomical details are poorly defined. Isotopic renography is probably the most widely used test to assess obstruction as it offers anatomical details and allows a functional evaluation of the kidney. The most commonly used radiopharmaceuticals are Tc99-DTPA, which is a purely glomerular agent, and Tc99-MAG3, which is extracted by the kidney and whose clearance is dependent on renal plasma flow and not on GFR. Due to the low neonatal GFR and the presence of artefacts secondary to the high background activity, DTPA is less useful in neonates than MAG3, which is now the most widely employed radiopharmaceutical. To assess obstruction a renogram may be used in different ways, the most common of which is the diuretic renogram. The evaluation of different parameters, including differential renal uptake, time to peak activity, and time to half peak after frusemide washout, taken all together, allows a reliable assessment of a partial obstruction to the urinary flow. In the case of a megaureter, the test must be performed following a strict protocol. The child has to be well hydrated and the bladder must be emptied to avoid the obscuring effect of the full bladder on the distal ureter. In selected cases, when spontaneous voiding is not possible, a catheter should be placed in the bladder and left on drainage during the test. When assessing the megaureter for an obstructive pattern it is necessary to create two areas of interest and two curves, one over the kidney and the second over the terminal ureter. A drainage curve created only over the kidney may give the false appearance of a non-obstructed pattern, because the dilated ureter may act as a large compliant reservoir accommodating the urine coming from the kidney but without delivering it to the bladder. In addition, several studies have reported that, especially in the newborn and infant, many kidneys show stasis and a prolonged T½ even when subsequent follow up demonstrates adequate growth of the kidney and no functional damage. Many technical refinements have been proposed to ameliorate the reliability of the diuretic renogram in assessing obstruction; English et al. [15] described a modified method in which the diuretic is administered 15 min before the isotope injection rather than 20 min later, as in the standard procedure. This technique is reported to decrease the rate of false positive renograms in patients with massively dilated ureters.

413 Because real obstruction causes kidney damage, in 1990 Ransley et al. [16] suggested using singlekidney GFR as a method of detecting obstruction. They suggested that any hydronephrotic kidney whose individual GFR was less than 40% was probably obstructed; others have proposed figures as low as 35% or even 30% (normal values being 50 G 5%). These authors had the great merit of focusing on separate function rather than the drainage curve. This has largely been accepted, and a reduction in single-kidney GFR of more than 10% in follow-up diuretic renograms is a definite indication for shifting from conservative treatment to surgery. Other procedures that have not gained widespread popularity are the deconvolutional analysis of the renogram with the assessment of parenchymal transit time, and the extraction factor (EF) described by Heyman and Duckett [17]. The first technique is complex and time consuming, and probably not superior to the standard renogram in defining obstructed patients. The EF is defined as the percentage uptake of radioisotope by the kidneys 2e3 min after injection with radionuclide. The normal mean value in the newborn is 1.5% by each kidney, which increases to 2.5% at the end of the first year. The correlation coefficient with GFR is 0.92. If the EF is normal and equal to the contralateral EF the dilated unit is considered to be not obstructed. Doppler ultrasonography with measurement of resistive index (RI) has recently been proposed as a non-invasive method to diagnose obstructive uropathy. An RI of 0.70 is generally accepted as an upper level of normal in adults, but it has been shown that RI is age dependent and it generally is O0.70 in healthy infants. An RI threshold of 0.70 gave a sensitivity of 82%, a specificity of 62% and an overall accuracy of 76% in detecting obstruction. To increase both sensitivity and specificity of RI, it may be useful to hydrate the patient before the test and give intravenous frusemide, thus lowering the resistive index in the normal kidney and increasing it in the obstructed one. The Whitaker [18] test is an invasive test that measures the pelvic pressure while saline at 10 ml/ min is infused into the collecting system; a pressure exceeding 22 cm H2O is considered to be significant for obstruction. This test is invasive and nonphysiological in children because saline is infused at a fixed rate, irrespective of the age of the patient, and the pressure values have not been validated for the paediatric population; therefore, it has been abandoned. Recently, Fung and associates [19] have modified the Whitaker test to make it more physiological

414 and adapted to use in the paediatric population. Pelvic pressure was assessed while simultaneously documenting the passage of contrast material from the ureter into the bladder; the infusion rate was individually calculated to keep it within a physiological range. In this setting, a pressure elevation of 14 cm H2O was considered to be indicative of obstruction. These modifications have made the test more physiological, but it still requires the establishment of a nephrostomy and its invasiveness has precluded its widespread use in children.

Treatment The treatment of an unobstructed non-refluxing megaureter is straightforward; these patients are generally asymptomatic with normal kidneys and, with expectant management, most do not experience a problem at any stage in their lives. More controversial is the management of POM. Some reports, dating back more than 10 years, described good results from early surgery. Both Peters et al. [20] and Mollard and Paillot [21] reported on two series of patients affected by POM and operated on in the first months of life with low morbidity and good overall results. These two papers have been criticised because both relied on IVP and drainage curves for assessing obstruction, and because it was not clear whether the reported improvement in kidney function observed during the follow up was the result of surgery or represented the natural improvement in function that usually occurs in postnatal life. Furthermore, the complication rate was rather high, in Peters’ series the reoperation rate being 12% [20]. In the last 15 years there has been an increasing move toward conservative management in asymptomatic cases discovered after prenatal sonography. There is no doubt that symptomatic megaureters, causing colicky pain, haematuria, febrile urinary tract infection etc., need prompt surgical treatment. Problems arise when we are confronted with a completely asymptomatic megaureter in a thriving infant without any sign of progressive kidney damage; these cases are becoming more and more frequent with the widespread use of prenatal ultrasound. Keating et al. [22] were the first, in 1989, to report on the non-operative management of 20 megaureters out of 23 diagnosed prenatally. Non-surgical management was selected on the basis of a normal extraction factor at DTPA renography. During the observation period, improved dilatation was observed in 15 and none showed signs of functional deterioration. Similar findings were reported by

E. Merlini, P. Spina Rickwood et al. [23], a few years later, who confirmed the safety of expectant management in prenatally diagnosed megaureters even if, according to renographic criteria, they appeared to be obstructed. Baskin et al. [24] published the results of a long follow up on the patients initially reported by Keating. After 7.3 years of observation, no patient showed increased dilatation or reduced function, and dilatation was reduced in 66.6% and stable in 33.3%. A more homogeneous series of 67 megaureters, all detected prenatally and managed conservatively, was reported by Liu and co-workers [25] from the Great Ormond Street Hospital. In this group, after 3.1 years’ follow up, 17% needed surgery for infection or deteriorating renal function, 49% remained stable and 34% resolved spontaneously. In these authors’ experience a ureteral diameter above 10 mm and slow drainage on DTPA scan were predictors of poor outcome. The same topic was recently addressed by McLellan et al. [26] who reported on the results and predictors of outcome for 69 prenatally detected megaureters. Among these, 10 (18.5%) underwent surgical repair because of severe hydroureteronephrosis and decreasing function, 39 (72%) returned to a normal size and five (9.5%) were unchanged. Megaureters whose diameter was less than 1 cm resolved more easily and quickly than those whose diameter was above 1 cm. Hydronephrosis was a good predictor of outcome. Grades 1e3 (according to the classification of the Society for Fetal Urology) tended to resolve between 12 and 36 months, while in children with grade 4 or 5 hydronephrosis or a larger than 1 cm retrovesical ureter the condition took longer to resolve or needed surgery. Recently, Stehr et al. [27] have reported that only 11.9% of 42 paediatric patients affected by POM and followed from 5 to 48 months required surgery because of impaired function at onset or deterioration of either function or urine drainage during follow up. All patients with a megaureter on expectant management should take antibiotic prophylaxis. The present authors have followed conservatively 29 neonatal megaureters for 5 years: of these 20.6% resolved, 34.4% showed improved dilatation, 34.4% were unchanged and 10.3% worsened, requiring surgery. All the published series of patients show that expectant management of prenatally detected megaureters is a safe practice, and that the operation rate in these patients ranges from 10 to 20%. The main criterion adopted by the different authors to change treatment and submit a patient to surgery is reduced renal function at onset or during follow up, but the degree of separate renal

Primary non-refluxing megaureters function for which a patient is shifted to surgery is still largely a personal choice. An increase in size of the ureter is a phenomenon that often precedes functional decline, as does the onset of symptoms such as pain, haematuria, urinary tract infections and the presence of calculi in the ureter. In the present authors’ view also a ‘giant’ megaureter, whose diameter exceeds 3 cm, is worth treating surgically after at least 2 years of conservative treatment.

Temporizing procedures In a newborn or infant it is probably unsafe to embark on an extensive operation such as tapering and re-implanting the ureters, because in most cases expectant therapy is sufficient. In rare cases, when a surgical approach is warranted because of increasing ureteral dimensions or of rapidly declining renal function, some form of ureteral diversion is needed [28,29]. A cutaneous ureterostomy is safe and easy to perform, but recently Ransley et al. [16] have proposed inserting a JJ stent in the megaureter to bypass the obstruction. The JJ may be introduced endoscopically or, more easily, through a small open cystotomy. This technique, even if not widely adopted, has some advantages over ureterostomy, as it avoids an external stoma, allows a free flow of urine to the bladder, and often reduces the megaureter diameter, making ureteral tapering at definitive surgery unnecessary.

Definitive procedures The surgical treatment of POM should allow the aperistaltic, narrow segment to be excised, and the ureter re-implanted in the bladder with an anti-reflux technique creating a tunnel whose length should be at least five times the ureteral diameter. In order to obtain such a ratio when the ureter’s calibre is wider than 10 mm, the last 10e 12 cm of ureter need to be tapered. Sometimes it is necessary to hitch the bladder to the psoas muscle in order to obtain a sufficiently long tunnel with a fixed entry point for the ureter. Three procedures have been reported for reducing the urethral calibre, described as follows. Excisional tapering of the ureter as described by Hendren [30] is accomplished by removing a longitudinal strip of the distal portion of the ureter. Only the ureter that will be accommodated in the submucosal tunnel and a few centimetres proximally need to be reduced in calibre. The transition from the dilated part to the tapered one must be

415 gradual and smooth to avoid kinking of the ureter. An 8e10-Fr. Jacques catheter is inserted into the ureter and held in place with some Babcock or Hendren clamps. The redundant part of the ureter on the less vascularized side is removed, and the ureter is sutured in two layers and then reimplanted into the bladder according to the LeadbetterePolitano or Cohen techniques. The ureters are generally left stented for 7e10 days. When the ureter is not excessively dilated, i.e. no more than 10e12 mm in diameter, a folding technique as described by Starr [32] or Kalicinski et al. [31] can be carried out. Kalicinski et al. were the first to report, in 1977, the technique of ureteral folding, later modified by Starr. The lateral, avascular side of the ureter is excluded from the lumen of the ureter by a running longitudinal suture, and then is folded posteriorly and secured with multiple sutures. The ureter is then re-implanted into the bladder following one of the usual procedures. Starr modified this procedure, introducing many interrupted Lembert sutures that folded the ureteral wall inward. The folding techniques have the advantage of preserving the blood supply of the ureter but the disadvantage that the plicated segment of ureter is often quite bulky and stiff. This may make subsequent ureteroneocystostomy cumbersome. Stents are optional, but we prefer to leave a ureteral catheter for at least 2 days. Our favourite techniques are the Starr folding procedure for ureters less than 10 mm wide, and a variation of the ureteral tapering procedure for larger ureters (Fig. 5) described as follows. The ureter is approached extravesically in the paravesical space, then it is detached from the bladder and the hiatus is closed with a stitch. All the bands that kink the distal third of the ureter are removed, being careful not to jeopardize the blood supply, a thin catheter is introduced into the aperistaltic segment, a ligature is tied around the distal end of the ureter, and saline is injected to blow up the ureter. Once the ureter is distended, a longitudinal incision is made that cuts only through the adventitia in the least vascularized portion, and the adventitia is then detached from the muscularis with great care in order to preserve all the blood vessels. When a triangular segment of the ureteral wall with a proximally oriented apex of sufficient length and width has been denuded of adventitia, it is resected. The two mucosal and muscular edges of the ureteral wall are approximated with a running locked suture, generally in 6/0 polydioxanone over a 10-Fr. Jacques catheter. The adventitia with the blood vessels is wrapped around the ureter to cover the first suture line and closed with a second running

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Figure 5

Surgical technique: ureteral tapering.

suture. The running suture must be stopped 2 or 3 cm before reaching the end of the ureter, and only interrupted sutures should be used distally in order to avoid the risk of jeopardizing the running suture if the ureter’s length is excessive and the distal end should be resected. The bladder is then opened, and the bladder wall is secured to the psoas muscle with a few 3/0 polydioxanone stitches in order to obtain a long and fixed area of the posterior bladder wall in which to place the ureter. A long and straight submucosal tunnel is developed from the stitched point to immediately above the bladder neck, and the ureter is re-implanted according to Paquin within this long submucosal tunnel [33]. This procedure allows the ureter to be placed in a very long tunnel without the risk of kinking it. The extravesical approach to the ureter enables the submucosal tunnel to be prepared in an untouched bladder, without excessive bleeding or mucosal oedema. Reported results of POM surgery are generally very satisfactory with a success rate of almost 90%.

References [1] Cussen LJ. The morphology of congenital dilation of the ureter: intrinsic ureteral lesions. Aust NZ J Surg 1971;31: 185. [2] Hellstrom M, Hjalmas K, Jacobsson B, Jodal U. Ureteral diameter in low-risk vesicoureteral reflux in infancy and childhood. Acta Radiol Diagn (Stockh) 1986;27:77e83. [3] King LR. Megaloureter: definition, diagnosis and management. J Urol 1980;123:222e3. [4] Shokeir AA, Nijman RJ. Primary megaureter: current trends in diagnosis and treatment. BJU Int 2000;86:861e8. [5] Swenson O. A new concept of the pathology of megaloureters. Surgery 1952;32:367e71. [6] Tanagho EA, Smith DR, Guthrie TH. Pathophysiology of functional ureteral obstruction. J Urol 1970;104:73e88.

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