Megaureter in Children: Causes, Diagnosis & Treatment Options

What is a Megaureter?

Mega + Ureter means megaureter, as the name defines it, is an enlarged ureter condition. 

• The normal ureteral diameter in children is rarely > 5 mm. A megaureter is defined as a ureter with a diameter greater than 7 mm. The dilated ureter, or MGU, can be classified into one of four groups based on the cause of the dilatation:
  • Refluxing
  • Obstructed
  • Both refluxing and obstructed
  • Both non-refluxing and non-obstructed
• The incidence of megaureter in antenatally diagnosed urological anomalies is around 20%, which is much higher than in the historical series because most were discovered only after they become symptomatic.
• However, if left undetected, many cases might never become symptomatic, which raises serious questions with regard to treatment.

Common Clinical Findings in Neonates 

• The common findings in neonates are referred for urological evaluation.
• Prenatal USG series suggest UVJ obstruction in up to 23% of patients with urinary tract dilatation
• Primary MGU is two to four times more common in boys than girls, has a slight prediction (1.6 to 4.5 times) for the left side, and is bilateral in app. 25% of patients.
• In up to 10% to 15% of children, the contralateral kidney may be absent or dysplastic, and concomitant obstruction of the ipsilateral UPJ area has been described on rare occasions.
• No clear evidence of hereditary predisposition.
• Clinically, patients have UTIs, PAIN, or HEMATURIA.

Pathophysiology 

• The distal end of the ureter, as it becomes intramural and subsequently sub-mucosal, rearranges the muscular layers in\ its wall.
• All layers become longitudinally oriented, and the ureter adventitia fuses to the bladder, triggered by attachment to Waldyer's sheath.
• Sympathetic and parasympathetic innervations to the distal ureter and UVJ area is believed to modulate primarily ureteral peristalsis; however, its exact role in regulating urine transport is unclear
• Peristalsis initiated by interstitial cells of Cajal in the minor calyx is the main mechanism of urinary transport in the ureter.
• Ureterovesical junction obstruction can occur in up to 23% of cases with ureteral dilatation on prenatal ultrasound.

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How Can We Classify a Megaureter?

Primary Refluxing Megaureter 

• Primary refluxing megaureter is associated with congenital anomalies and deficiency of longitudinal muscles of the intravesical ureter, causing inadequate valve mechanisms and urine reflux.
• The cause of primary obstructive MGU typically is an aperistaltic juxta vesical 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 (Type 1) have been described.
• 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.
• The most common cause of primary obstructive megaureter is aperistaltic segment 3-4 cm in the distal part of the ureter, leading to accumulation of urine in the ureter and then dilatation.

Secondary Obstructive Megaureter

• Secondary refluxing megaureter is caused by bladder obstruction or elevated pressure that accompany it.
  • Examples include PUV (most common) as well as neurogenic bladders and non-neurogenic bladders and Prune Belly.
• Most commonly occurs with neurogenic and non neurogenic voiding dysfunction or intravesical 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 of the ureter is reversible once the elevated intravesical pressure is relieved.
• Altered compliance or damaged peristaltic mechanisms can cause the ureter to remain dilated.
• 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 post-reimplantation fibrosis, neurogenic bladder, and external compression by retroperitoneal tumors, masses, or aberrant vessels.

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Primary Non-Obstructive Non-Refluxing Megaureter

• Once VUR, obstruction, and secondary causes of dilatation have been ruled out diagnosis of primary non-refluxing, 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
• The newborn ureter is a more compliant conduit than that of the adult.
• The kidneys of a newborn are probably better buffered from the pressure 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.

Secondary Nonobstructive, Non-Refluxing Megaureter

• Non-obstructive, non-reflexive megaureter is more common than originally thought and can result from acute UTI with bacterial endotoxins that inhibit peristalsis. (Resolution with appropriate antibiotic therapy)
• Nephropathies and other conditions lead to increased UOP (urine output production) that overwhelms max peristalsis, which leads to progressive dilation.
• These include lithium toxicity, diabetes insipidus or mellitus, sickle cell nephropathy, and psychogenic polydipsia.
• The most extreme example of non-obstructive megaureter occurs with Prune Belly syndrome.

Prevalence 

• Clinically significant megaureter accounts for 8% of children with urological problems, with UPJO being the most common problem.
• Prevalence of megaureter is around 20%, but clinically significant incidence is only 8%.
• MGU are reported to occur in approx. 23% of neonates noted to have antenatal hydroureteronephrosis
• Megaureter is more common in boys and on the left side.
• Ranking 2nd in D/D of neonates with hydronephrosis after UP obstruction.

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Investigation of Megaureter in Children?

• Ultrasound is the initial investigation for any child with a suspected urinary abnormality.
• It distinguishes the MGU from the UPJ as the most common cause of hydronephrosis.
• Ultrasound distinguishes between hydronephrosis and hydroureteronephrosis, which can help diagnose the underlying condition.
• If it was just hydronephrosis, probably it is UPJ. But if it was hydroureteronephrosis, then definitely it is MGU.
• Ultrasound provides useful anatomical information about renal parenchyma and collecting system bladder.
• It also gives a baseline standard for the degree of hydroureteronephrosis for future studies.
• If there is ureteral dilation, a VCUG should be performed to rule out reflux and assess the quality of the bladder and urethra.
• In MGU, one needs to look for whether the reflux is occurring or not, whether the bladder is compliant or not, and whether there is any distal obstruction or not.
• Neurogenic dysfunction and outer obstruction are common causes of secondary mechanisms, and renal function needs to be assessed.
• 99m Tc-DTPA and 99m Tc-Mertiatide (MAG3) are most commonly used to assess function and clearance.

Shortcoming of the Renal Scan

• Standardized tracer dosing as different kinds of centers might give different doses of this particular radioisotope.
• Renal scan offers an objective, reproducible parameter of the function and obstruction.
• Renal scans should be performed after three months for glomerular maturation.
• Scans that evaluate drainage that is a half life alone routinely yield a value indicative of an obstruction because of a dilation of the collecting system.
• Drainage evaluation using a DTPA scan can indicate obstruction in the collecting system.
• The renal scan estimate, that is, the GFR and absolute renal function by measuring the uptake of the radionuclide (DTPA) early after the systemic administration.
• There is no control over how much of that particular radio tracer will be passing through that particular area of interest, but if the kidneys function properly, the uptake of this particular radio tracer would be good. So essentially, the GFR indicates the impact of the megaureter on the renal parenchymal levels rather than within the collecting system, where slow rates of washout are to be expected because of the dilation.
• So even though it's hard to assess how much of the pelvis is dilated and what is the effect going to happen to the movement of the radiotracers into the renal pelvis and the urinator, if all the kidneys are functioning properly, the radiotracer will be picked up properly.
• Magnetic resonance urography has the capability of providing greater anatomic abnormalities.
• Percutaneous perfusion studies (Whitaker perfusion test) can also be used.

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Recommendations for Primary Refluxing Megaureter 

• The routine recommendation of surgery in newborns and infants with grades IV and V is appropriate.
• The patient is initially put on medical management of antibiotics along with routine observation for at least five years before considering surgery.
• Medical management is appropriate during infancy and can be continued if the trend of resolution is observed.
• Surgery is recommended for persistent high-grade reflux in older adults and those with recurrent UTIs.
• Distal ureterostomy for unilateral reflex or vesicostomy for bilateral disease can provide a temporary solution for patients who are too small for reconstruction surgery or if the medical management has failed.

Recommendations for Secondary Refluxing or Obstructive Megaureter 

• Management of the secondary MGUs is directed at the cause.
• The reflex and dilatation improve with the ablation of PUV or medical management of the neurogenic bladder.
• MGUs from prune belly syndrome, diabetes insipidus, or infection require no more than observation alone.
• Non-obstructive hydroureteronephrosis may persist even after primary and secondary causes are corrected, and regular re-evaluation is necessary.

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Recommendations for Primary Non-Obstructive, Non-Refluxing Megaureter

• The complication rate of surgery is higher in infants.
• Repeat surgeries were required for 12% of infants operated on before 8 months in one series. Don't rush for the surgery, as the chances of complications are higher in infants.
• 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.
• 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.

Surgical Options for Megaureter in Children 

• Ureteral tailoring is usually necessary to achieve the proper length-to-diameter ratio, which is 5:1.
• Narrowing of the ureter may enable the walls to co-apt, 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, leading to peristaltic recovery
• 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, as folding it makes it very bulky.
• Excisional tapering is preferred for the more severely dilated or thickened ureter.
• Plication of ureters greater than 1.75 cm in diameter experienced more complications in one series
• 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.
• Compared to 95-99% of non-megaureter reimplants.

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