2Definition Normal ureteral diameter in children is rarely > 5 mm Ureters > 7 mm are considered MGUsThe dilated ureter or MGU can be classified into one of four groups based on the cause of the dilatation:(1) refluxing(2) obstructed(3) both refluxing and obstructed(4) both nonrefluxing and nonobstructed.
3MegauretersIn one series, MGU comprised 20% of antenatally diagnosed urologic anomalies, much higher than in historical series b/c most were discovered only after they became symptomaticIf left undetected, many MGUs might never become symptomaticAn observation that raises serious questions with regard to treatment
4Primary and Secondary Refluxing Megaureter Primary refluxing megaureters are associated with congenital anomalies of the UVJ where a deficiency of the longitudinal muscle of the intravesical ureter results in an inadequate valvular mechanismSecondary refulxing megaureters are caused by bladder obstruction and the elevated pressures that accompany itExamples include PUV (most common) as well as neurogenic bladders and non-neurogenic neurogenic bladders
5Primary Obstructive Megaureter The cause of primary obstructive MGU typically is an aperistaltic juxtavesical segment 3 to 4 cm long that is unable to propagate urine at acceptable rates of flowTrue stenosis is rare, but histologic disorientation of muscle, muscular hypoplasia, muscular hypertrophy, mural fibrosis and excess collagen deposition have been described
6Primary Obstructive Megaureter Altered peristalsis prevents the free outflow of urineRetrograde regurgitation occurs as urine boluses are unable to fully traverse the aberrant distal segmentResulting ureteral dilatation depends on the amount of urine that is forced to coalesce proximally because of incomplete passage.Other rare causes of primary obstructive MGU include congenital ureteral strictures and ureteral valves
7Secondary Obstructive Megaureter Most commonly occurs with neurogenic and non- neurogenic voiding dysfunction or infravesical obstructions such as PUVThe ureter struggles with propulsion of urine when pressure is > 40 cm H2O across the UVJ.Ureteral dilatation, decompensation of the UVJ, reflux, and renal damage result if pressures continue uncheckedDilatation largely resolves once the elevated intravesical pressures are addressed
8Secondary Obstructive Megaureter Sometimes, the ureter remains dilated due to altered compliance or a damaged peristaltic mechanisms.Transmural scarring from chronic infection is seen in some cases.Obstruction is not truly present but elevated intravesical pressures are projected proximally as a noncompliant columnOther obstructive causes of ureteral dilatation include ureteroceles, ureteral ectopia, bladder diverticula, periureteral postreimplantation fibrosis, neurogenic bladder, and external compression by retroperitoneal tumors, masses, or aberrant vessels
9Primary Nonobstructive, Nonrefluxing Megaureter Once VUR, obstruction, and secondary causes of dilatation have been ruled out diagnosis of primary nonrefluxing, nonobstructive MGUMost newborn MGUs fall in this categoryPossible causes: increased fetal UOP, persistent fetal folds, delayed ureteral patency, immature peristalsis, hyperreflexic bladder of infancy, transient urethral obstruction
10Primary Nonobstructive, Nonrefluxing Megaureter The newborn ureter is a more compliant conduit than that of the adultThe kidneys of newborns are probably better buffered from the pressures of any partial or transient obstructions that might occur early in development than are kidneys obstructed at more proximal levels (UPJ) or at a later age
11Secondary Nonobstructive, Nonrefluxing Megaureter More common than originally thought, and often have an identifiable causeCan result from acute UTI with bacterial endotoxins that inhibit peristalsisResolution with appropriate antibiotic therapyNephropathies and other conditions lead to increased UOP that overwhelm max peristalsis which leads to progressive dilatation
12Secondary Nonobstructive, Nonrefluxing Megaureter These include lithium toxicity, diabetes insipidus or mellitus, sickle cell nephropathy, and psychogenic polydipsiaThe most extreme examples of nonobstructed ureteral dilatations occur with the prune-belly syndrome
13EvaluationUltrasound is the initial study obtained in any child with a suspected urinary abnormalityUsually distinguishes MGU from UPJ as the most common cause of hydronephrosisProvides useful anatomic detail of the renal parenchyma, collecting system, and bladderBaseline standard for the degree of hydroureteronephrosis for serial f/u studies
15Evaluation The presence of ureteral dilatation VCUG to rule out reflux and assess the quality of the bladder and urethraNeurogenic dysfunction or outlet obstruction are common causes of secondary MGUNeed to assess renal function
16EvaluationNRS offers objective, reproducible parameters of function and obstruction99m Tc-DTPA and 99m Tc-Mertiatide (MAG3) are most commonly used assess function and clearance.NRS shortcomings: standardized tracer dosing, timing in diuretic dosing, and patient hydration ensure valid comparison of resultsshould defer the study for 3 months for glomerular maturationScans that evaluate drainage (half-life) alone routinely yield values indicative of obstruction because of the dilatation of the collecting system
17EvaluationNRS can estimate GFR and absolute renal function by measuring the uptake of radionuclide (DTPA) early after its systemic administrationThis may indicate the impact of megaureter on renal parenchymal level, rather than within the collecting system, where slow rates of washout are to be expected because of dilatation
19Recommendations: Primary Refluxing Megaureter Routinely recommending surgery in newborns and infants with grades IV-V reflux is not appropriateMedical management is appropriate during infancy and is continued if a trend to resolution is notedSurgery remains the recommendation for persistent high- grade reflux in older children and adultsIn the rare infant for whom medical management has failed but who is considered too small for reconstructive surgery, distal ureterostomy for unilateral reflux or vesicostomy for bilateral disease provides an ideal temporizing solution
20Recommendations: Secondary Refluxing or Obstructive Megaureter Management of secondary MGUs is directed at their causeReflux and dilatation improve with the ablation of PUV or medical management of neurogenic bladderMGUs from prune-belly syndrome, diabetes insipidus, or infection, require no more than observation aloneSome degree of nonobstructed hydroureteronephrosis usually persists, even after primary or secondary causes have been correctedRe-evaluation is often necessary
21Recommendations: Primary Nonobstructive, Nonrefluxing Megaureter The complication rate of surgery is higher in infantsrepeat surgeries were required for 12% infants operated on before 8 mo in one seriesAs long as renal function is stable and UTIs are not a problem, expectant management is preferredAntibiotic suppression with close radiologic surveillance is appropriate in most casesU/A and RUS every 3 to 6 months during the first year
22Recommendations: Primary Nonobstructive, Nonrefluxing Megaureter Severe hydroureteronephrosis that shows no signs of improvement or the clinical status worsens, correction is undertaken when it is technically feasible, usually between the ages of 1 and 2 years.For the occasional newborn who presents with massive ureteral dilatation or poor renal function (which is rare with MGUs) or develops recurrent infections, distal ureterostomy provides an effective means for poor drainage until the child is old enough to undergo reimplantation.
23Surgical OptionsUreteral tailoring is usually necessary to achieve the proper length-to-diameter ratioNarrowing of the ureter may enable the walls to coapt, leading to more effective peristalsisRevising the distal segment intended for reimplantation is all that is usually requiredThe proximal segments regain tone once they are unobstructed. Kinking is usually nonobstructive and will resolve.Extended stent drainage after tapering decompresses the systemLeads to peristaltic recovery
24Surgical OptionsPlication or infolding is useful for the moderately dilated ureter.Ureteral vascularity is preserved, and the revision can be taken down and redone if vascular compromise is suspectedBulk is a problem with the extremely large ureterExcisional tapering is preferred for the more severely dilatated or thickened ureterPlication of ureters greater than 1.75 cm in diameter experienced more complications in one series
25Surgical OptionsRemodeled MGUs have been generally reimplanted with standard cross-trigonal or Leadbetter-type techniquesExtravesical repairs can also be successfully doneThe success with reimplantation of remodeled MGUs is 90-95% regardless of techniqueCompares to 95-99% of non-megaureter reimplants
26Results and Complications The reimplantation of MGUs has the same complications (i.e., persistent reflux and obstruction) as that of nondilated ureters, but at increased ratesComplications can occur regardless of whether excisional tapering or a folding technique is usedBetter results with obstructive MGU and higher rates of unresolved reflux after tailoring of refluxing variantsHigher incidence of bladder dysfunction associated with the latter and more dramatic abnormalities of their musculature.
27Results and Complications Increased collagen deposition in refluxing MGUs and altered smooth muscle ratiosIn contrast, obstructive MGUs were not found to be statistically different from controlsIncreased levels of type III collagen in refluxing MGUsLeads to an intrinsically stiffer ureter that lessens the surgical success in reimplantationRarely, reflux persists despite adequate ureteral tunnels in both tapered and normal-sized ureters.Leads to intrinsic ureteral dysfunction caused by transmural scarring