Megaureter

1. Megaureter Stephen Confer, M.D. Pediatrics Didactic Presentation July 25, 2006

2. Definition • Normal ureteral diameter in children is rarely > 5 mm • Ureters > 7 mm are considered MGUs • The 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.

3. Megaureters • In 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 symptomatic • If left undetected, many MGUs might never become symptomatic • An observation that raises serious questions with regard to treatment

4. Primary 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 mechanism • Secondary refulxing megaureters are caused by bladder obstruction and the elevated pressures that accompany it • Examples include PUV (most common) as well as neurogenic bladders and non-neurogenic neurogenic bladders

5. Primary 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 flow • True stenosis is rare, but histologic disorientation of muscle, muscular hypoplasia, muscular hypertrophy, mural fibrosis and excess collagen deposition have been described

6. Primary Obstructive Megaureter • Altered peristalsis prevents the free outflow of urine • Retrograde regurgitation occurs as urine boluses are unable to fully traverse the aberrant distal segment • Resulting 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

7. Secondary Obstructive Megaureter • Most commonly occurs with neurogenic and non-neurogenic voiding dysfunction or infravesical obstructions such as PUV • The 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 unchecked • Dilatation largely resolves once the elevated intravesical pressures are addressed

8. Secondary 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 column • Other 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

9. Primary Nonobstructive, Nonrefluxing Megaureter • Once VUR, obstruction, and secondary causes of dilatation have been ruled out diagnosis of primary nonrefluxing, nonobstructive MGU • Most newborn MGUs fall in this category • Possible causes: increased fetal UOP, persistent fetal folds, delayed ureteral patency, immature peristalsis, hyperreflexic bladder of infancy, transient urethral obstruction

10. Primary Nonobstructive, Nonrefluxing Megaureter • The newborn ureter is a more compliant conduit than that of the adult • The 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

11. Secondary Nonobstructive, Nonrefluxing Megaureter • More common than originally thought, and often have an identifiable cause • Can result from acute UTI with bacterial endotoxins that inhibit peristalsis • Resolution with appropriate antibiotic therapy • Nephropathies and other conditions lead to increased UOP that overwhelm max peristalsis which leads to progressive dilatation

12. Secondary Nonobstructive, Nonrefluxing Megaureter • These include lithium toxicity, diabetes insipidus or mellitus, sickle cell nephropathy, and psychogenic polydipsia • The most extreme examples of nonobstructed ureteral dilatations occur with the prune-belly syndrome

13. Evaluation • Ultrasound is the initial study obtained in any child with a suspected urinary abnormality • Usually distinguishes MGU from UPJ as the most common cause of hydronephrosis • Provides useful anatomic detail of the renal parenchyma, collecting system, and bladder • Baseline standard for the degree of hydroureteronephrosis for serial f/u studies

15. Evaluation • The presence of ureteral dilatation • VCUG to rule out reflux and assess the quality of the bladder and urethra • Neurogenic dysfunction or outlet obstruction are common causes of secondary MGU • Need to assess renal function

16. Evaluation • NRS offers objective, reproducible parameters of function and obstruction • 99m 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 results • should defer the study for 3 months for glomerular maturation • Scans that evaluate drainage (half-life) alone routinely yield values indicative of obstruction because of the dilatation of the collecting system

17. Evaluation • NRS can estimate GFR and absolute renal function by measuring the uptake of radionuclide (DTPA) early after its systemic administration • This 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

19. Recommendations: Primary Refluxing Megaureter • Routinely recommending surgery in newborns and infants with grades IV-V reflux is not appropriate • Medical management is appropriate during infancy and is continued if a trend to resolution is noted • Surgery remains the recommendation for persistent high-grade reflux in older children and adults • In 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

20. Recommendations: Secondary Refluxing or Obstructive Megaureter • Management of secondary MGUs is directed at their cause • Reflux and dilatation improve with the ablation of PUV or medical management of neurogenic bladder • MGUs from prune-belly syndrome, diabetes insipidus, or infection, require no more than observation alone • Some degree of nonobstructed hydroureteronephrosis usually persists, even after primary or secondary causes have been corrected • Re-evaluation is often necessary

21. Recommendations: Primary Nonobstructive, Nonrefluxing Megaureter • The complication rate of surgery is higher in infants • repeat surgeries were required for 12% infants operated on before 8 mo in one series • As long as renal function is stable and UTIs are not a problem, expectant management is preferred • Antibiotic suppression with close radiologic surveillance is appropriate in most cases • U/A and RUS every 3 to 6 months during the first year

22. Recommendations: 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.

23. Surgical Options • Ureteral tailoring is usually necessary to achieve the proper length-to-diameter ratio • Narrowing of the ureter may enable the walls to coapt, leading to more effective peristalsis • Revising the distal segment intended for reimplantation is all that is usually required • The proximal segments regain tone once they are unobstructed. Kinking is usually nonobstructive and will resolve. • Extended stent drainage after tapering decompresses the system • Leads to peristaltic recovery

24. Surgical Options • Plication 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 suspected • Bulk is a problem with the extremely large ureter • Excisional tapering is preferred for the more severely dilatated or thickened ureter • Plication of ureters greater than 1.75 cm in diameter experienced more complications in one series

25. Surgical Options • Remodeled MGUs have been generally reimplanted with standard cross-trigonal or Leadbetter-type techniques • Extravesical repairs can also be successfully done • The success with reimplantation of remodeled MGUs is 90-95% regardless of technique • Compares to 95-99% of non-megaureter reimplants

26. Results and Complications • The reimplantation of MGUs has the same complications (i.e., persistent reflux and obstruction) as that of nondilated ureters, but at increased rates • Complications can occur regardless of whether excisional tapering or a folding technique is used • Better results with obstructive MGU and higher rates of unresolved reflux after tailoring of refluxing variants • Higher incidence of bladder dysfunction associated with the latter and more dramatic abnormalities of their musculature.

27. Results and Complications • Increased collagen deposition in refluxing MGUs and altered smooth muscle ratios • In contrast, obstructive MGUs were not found to be statistically different from controls • Increased levels of type III collagen in refluxing MGUs • Leads to an intrinsically stiffer ureter that lessens the surgical success in reimplantation • Rarely, reflux persists despite adequate ureteral tunnels in both tapered and normal-sized ureters. • Leads to intrinsic ureteral dysfunction caused by transmural scarring