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