Obstructed Megaureter 

Updated: Mar 23, 2021
Author: Robert A Mevorach, MD; Chief Editor: Edward David Kim, MD, FACS 


Practice Essentials

Megaureter, the accepted term for the dilated ureter, is divided into primary (congenital) and secondary categories. Each category is further subdivided into (1) refluxing nonobstructing megaureter and (2) nonrefluxing obstructing megaureter. These distinctions are based on radiographic and clinical findings. This article discusses primary obstructive megaureter.

Obstructive megaureter is, in itself, a misnomer because most cases demonstrate only partial obstruction. Although this entity is rare, the principles of its evaluation and management may apply to a wide spectrum of ureteral abnormalities; consequently, a thorough understanding has a wide application.

Congenital and acquired lesions that cause obstruction of the distal ureter have been reported, and, in certain instances, these lesions confound the diagnosis. While a primary obstructed megaureter may subtend both single and the duplicated collecting systems, it is associated most commonly with a single system. Lesions may include the following:

  • Ureteroceles are more common in females and are associated with the upper-pole ureter of a complete duplication of the renal collecting system. Protrusion of the dilated distal ureter within the bladder or urethral lumen defines this lesion.

  • Ureteral valves, membranes, and polyps demonstrate intrinsic filling defects that differentiate these lesions from primary megaureter. These lesions are rare.

  • Ureteral calculi may become impacted in the distal ureter and may be associated with scarring. The resultant ureteral narrowing may obscure the underlying diagnosis; however, management principles are consistent, regardless of the underlying pathology.

The diagnosis of obstructed megaureter is established radiographically based on definition of a dilated distal ureteral segment that inserts into a normal ureteral meatus. Findings on endoscopy reveal that these ureteral tunnels allow retrograde passage of a ureteral catheter or probe. However, when viewed fluoroscopically, the peristalsis of the ureter, which halts abruptly at the narrowing, can be observed. Associated abnormalities may include the following:

Increasing ureteral dilation warrants consideration of renal and ureteral drainage. Megaureters detected in neonates and infants may require drainage for infections that do not respond to antibiotics alone. Additionally, the massively dilated ureter may be decompressed with ureterostomy, pyelostomy, or nephrostomy drainage, which often allows a substantial decrease in ureteral size and greatly reduces ureteral bulk during both tailoring and reimplantation. In mild cases of obstructed megaureter, surgery may be unnecessary. Physicians may monitor symptoms, perform periodic radiologic imaging, and administer antibiotic prophylaxis.

As with all reconstructive procedures, the belief that recapitulation of anatomy is necessary to achieve excellent functional results is tested continually by the desire to minimize the extent and duration of surgical invasion. When patients are well-served, finding fault with either approach is difficult. The next wave of interest will arise from the growing trend toward minimally invasive surgery and the application of improved laparoscopic and robotic techniques to reconstructive pediatric urology.

History of the Procedure

In 1923, Caulk described a patient with distal ureteral dilatation without evidence of hydronephrosis and coined the term megaloureter. Thirty years later, Swenson postulated a neurologic etiology for both megacolon and megaureter and treated such patients with urinary diversion, ureteral substitution, and ileal augmentation to provide peristalsis. Clinical management of megaureter evolved over the next two decades. Stephens, Nesbitt, and Withycombe advised observation and double voiding to reduce the incidence of urinary tract infections (UTIs) and admonished those who practiced the surgical approaches of the period.

Johnston, Hendren and Henderson, and Creevy advanced the field of surgical management of megaureter through aggressive ureteral tailoring and the adaptation of experience in ureteral reimplantation for vesicoureteral reflux.[1, 2, 3] Williams and Hulme-Moir launched the era of modern care of the primary megaureter by demonstrating a spectrum of this disorder that could be managed with observation in less-severe cases, with excellent clinical and radiographic outcomes.[4]


Partial obstruction in the abnormal distal segment of the ureter leads to progressive dilatation. Progression to hydronephrosis (ie, dilation of the renal pelvis and calyces) occurs when the ureter no longer accommodates resistance to urinary drainage; pressure is then conveyed more proximally. Complete obstructions are rare and are invariably associated with a nonfunctioning renal unit at diagnosis.

Primary obstructed megaureters enter the bladder in a normal location on the trigone, with the ureteral orifice appearing unaffected. This entity should not be confused with ectopic megaureters that end in an abnormal location within the lower urinary tract or other mesonephric anlage.


Primary obstructing megaureter is caused by a structural alteration in the muscular layers of the distal ureter, which is characterized to varying degrees by diminished or absent longitudinal muscle fibers, hypertrophied or hyperplastic circular muscle fibers, or increased connective-tissue deposition. These changes are defined pathologically and may represent either an arrest of normal development or an intrauterine response of the ureter to ongoing obstruction.[5]

Animal models of congenital megaureter are lacking, but Mortell et al have developed a rat model of prenatal doxorubicin (Adriamycin) exposure that may help elucidate the etiology of this developmental defect.[6]


The incidence of obstructed megaureter is 1 per 10,000 population. The male-to-female ratio is 1.2-4.8:1. The left-to-right ratio is 1.7-4.5:1. Obstruction is bilateral in 10%-20% of obstructed megaureter cases. 

Primary obstructive megaureter (POM) is common in children, with an increasing incidence since the advent of fetal ultrasonograpy. In adults, this condition is quite uncommon and only occurs after decades of remaining asymptomatic without any spontaneous regression.[7]




Prenatal ultrasonography reveals an indication of an underlying genitourinary abnormality in as many as 1 per 100 births; most of these are hydronephrosis. Clinical presentation of primary megaureter, which is less common since the advent of fetal ultrasonography, includes the following:

In children, megaureter may also be identified serendipitously on imaging  studies(eg, ultrasonography; CT scanning; kidneys, ureters, and bladder [KUB] radiography; bone scan) performed for other indications.



Laboratory Studies

Basic metabolic panel

Relevant findings on a basic metabolic panel include the following:

  • Creatinine and blood urea nitrogen (BUN) levels allow assessment of gross kidney function.
  • Sodium, potassium, chloride, or bicarbonate levels may show subtle changes in some patients with bilaterality or associated dysplasia.
  • A creatinine level of 1 mg/dL or greater at age 1 year is prognostic for subsequent renal failure.
  • A serum calcium assessment for associated ureteral calculi is an essential screening test for hyperparathyroidism.

However, note that blood samples taken in the first few days of life will not provide an accurate reflection of the neonate's kidney function, because the creatinine levels will be influenced by the mother's kidney function. Serum creatinine crosses the placenta, which results in high levels at birth and for the first 72 hours of life, due to the infant's difficulty in eliminating excess creatinine transferred in utero. Serum creatinine values show a steady decline and reach stable levels by 1 to 2 weeks of age in term neonates, or 3 to 4 weeks in preterm neonates.[8]


Urinalysis is used to screen for urinary tract infection (UTI) and assess urine concentration and acidification in patients with bilateral lesions and dysplasia. However, proteinuria, high pH, and low specific gravity may reflect underlying infection or renal dysplasia or damage.

Imaging Studies

Prenatal renal or bladder ultrasonography (see the images below) reveals both hydroureter and hydronephrosis. If hydronephrosis is found, in a fetus with solitary kidney or bilateral lesions, ultrasonography should be repeated within the first few days of life. Hydroureter and unilateral lesions may be evaluated electively within the first 2 months of life.

This renal sonogram demonstrates hydronephrosis wi This renal sonogram demonstrates hydronephrosis with good parenchymal thickness and retained corticomedullary differentiation.
This pelvic sonogram reveals the classic spindle c This pelvic sonogram reveals the classic spindle configuration of primary obstructed megaureter.

Postnatal imaging is used to define the degree of hydronephrosis based on the following Society of Fetal Urology guidelines:

  • Grade I - Splitting of the renal sinus more than 10 mm
  • Grade II - Splitting of the renal sinus more than 10 mm in an extrarenal or intrarenal pelvis not extending to the calyces
  • Grade III - Dilatation extending into the calyces without cortical thinning
  • Grade IV - Dilatation extending into the calyces with cortical thinning

Postnatal imaging further defines the following anatomy:

  • Extent of hydroureter, presence of collecting system duplication
  • Presence or absence of ureterocele
  • Bladder configuration, size, and thickening

Postnatal imaging further provides clinically relevant data, including the following:

  • Presence or absence of calculi
  • Echogenic debris suggesting infection
  • Indirect evidence of degree of obstruction by presence of a ureteral jet
  • Location and condition of remaining renal units

Voiding cystourethrography (VCUG) is performed to assess for the presence of vesicoureteral reflux and to further delineate the anatomy of the bladder and outlet. In boys with bilateral megaureter, posterior urethral valves must be excluded.

Radionuclide renal scanning

After ultrasonography and VCUG are performed, the diagnosis of primary megaureter may be secure; the only remaining clinical issue is evaluating for obstruction. In these cases, technetium Tc 99m diethylenetriamine pentaacetic acid (DTPA) or technetium Tc 99m mercaptotriglycylglycine (MAG-3) renal scanning may be used to assess renal blood flow, relative function, and drainage. It is also helpful in predicting the capacity for functional recovery prior to surgery.

Increasing ureteral dilation warrants consideration of renal and ureteral drainage. Although kidney drainage may be normal, it may be the result of urine pooling in the abnormally dilated ureter, resulting in ureteral obstruction.

Exact definitions of obstruction do not exist. Serial examinations to demonstrate a trend toward decreasing function or delayed drainage are often required to establish an accurate treatment approach. In addition, renal resistive index can be used to help identify true obstruction as long as renal function is good.[9]

This panel from a technetium Tc 99m mercaptotrigly This panel from a technetium Tc 99m mercaptotriglycylglycine (MAG-3) renal scan shows differential obstruction of each kidney. While the classic image of a primary obstructed megaureter is shown on the left, a severe congenital ureteropelvic junction obstruction is present in the contralateral kidney. (These images are viewed with the left kidney on the left portion of each panel and the right kidney on the right portion of each panel.)

Intravenous urography: In cases in which anatomic definition is desired, intravenous urography (IVU) can be used if renal function is good and the degree of obstruction to the affected renal unit is mild.

Magnetic resonance imaging: In centers that have the technology, MRI can be used to reconstruct a 3-dimensional depiction of the urinary collecting system. The requirement for special software to assess renal function accurately and the need for restraint, sedation, or general anesthesia limit its application in neonates and infants.

Diagnostic Procedures

Antegrade injection of contrast directly into the renal pelvis via percutaneous access is used as an adjunct to placement of a nephrostomy tube to drain an infected system or to define an equivocal obstruction (Whitaker test) by infusion of contrast medium at a fixed rate with concurrent pressure measurements in the kidney and bladder. Infusion rates for adults generally have been 10 mL per minute, and a pressure differential between kidney and bladder of less than 15 cm H2O is accepted as normal. This study is often used to provide additional evidence of obstruction to support surgical intervention. This technique also helps to delineate anatomy when diagnostic questions persist after less-invasive testing, often in the same setting as planned surgical repair.

As is evident from the 600-mL/h rate of urine flow that is used in the Whitaker test, the physiologic implications of all except negative test results are debatable. In the author's experience, this test is too dependent on variations in anatomy (renal collecting system compliance) and technique to provide any real benefit over a gestalt from antegrade pyelography alone.

Retrograde pyelography involves placement of a catheter into the ureteral meatus via endoscopy, with injection of contrast medium under real-time fluoroscopy. It is reserved for diagnostic dilemmas and as an adjunct to surgery.

Histologic Findings

Surgical pathology may reveal any of the following 5 histologic types:

  1. Abnormal circular orientation of muscle fibers with hypertrophy and hyperplasia
  2. Mural fibrosis with little normal muscle within the ureteral wall
  3. Hypoplasia and atrophy of all ureteral musculature
  4. Absent longitudinal musculature
  5. Normal ureteral anatomy


Medical Therapy

In mild cases of obstructed megaureter, physicians may monitor symptoms, perform periodic radiological imaging, and administer antibiotic prophylaxis. With improving or stable renal or ureteral dilatation and continued renal growth, prognosis (over 8 y of follow-up) is excellent.[10]

Antibiotics used for prophylaxis in these patients include the following:

Surgical Therapy

Megaureters detected in neonates and infants may require drainage for infections that do not respond to antibiotics alone. Additionally, the massively dilated ureter may be decompressed with ureterostomy, refluxing ureteroneocystostomy, pyelostomy, or nephrostomy drainage, which often allows a substantial decrease in ureteral size and greatly reduces ureteral bulk during both tailoring and reimplantation.[11, 12, 13, 14]

Endoscopic balloon dilation offers a minimally invasive treatment option for primary obstructive megaureter, with good long-term results.[15, 16] Chiarenza et al reported that is balloon dilation is effective in short stenotic tracts (< 5 mm), may also be repeated with good results in intermediate stenotic sections (5 mm-1 cm), and appears to be more effective if performed early in life (age 3-7 months).[17]

The ultimate goals of surgical intervention are to relieve obstruction, to return near-normal function to the collecting system, to create a nonrefluxing vesicoureteral reimplantation, and to preserve renal development without long-term complications. With these goals, the two main surgical approaches are as follows:

  • Distal ureteral mobilization with resection of the obstructing segment and reimplantation, with or without ureteral tailoring (to ensure a nonrefluxing tunnel)

  • Extensive tailoring of the ureter from the renal pelvis distally to provide a theoretical benefit for restoring normal peristalsis by reduction of ureteral luminal diameter

In experienced hands, both approaches yield excellent long-term results. Substantive differences are not statistically or clinically apparent.

Patients with voiding dysfunction or significant reflux may benefit from an intravesical ureteral reimplantation. Patients without voiding problems or reflux do equally well from an extravesical approach.

Laparoscopic-assisted extracorporeal ureteral tapering repair and ureteral extravesical reimplantation has been reported as a safe alternative to open surgery when the first line of treatment fails.[18] Rappaport et al reported that both laparoscopic and robot-assisted approaches are safe and effective for performing dismembered extravesical cross-trigonal ureteral reimplantation for pediatric patients with obstructed megaureter.[19]

Primary endoureterotomy with stenting has been reported favorably in selected cases in children. In one series, 90% of cases showed improvement, with complete resolution reported in 71%.[20]

In adults, a direct nipple ureteroneocystostomy can be performed. This is technically simpler to perform since the ureters and submucosal tunnels require no tailoring. Limited reports with follow-up of up to 36 months indicate a high success rate with this technique in adults.[21]

Preoperative Details

Document that patients are free of infection at the time of reconstruction. Blood loss is normally insubstantial, and transfusion is rarely necessary.

Intraoperative Details

Note the following:

  • The incision is chosen to access the upper ureter, the lower ureter, or the entire ureter. Use intravesical and extravesical dissection, alone or in combination, to mobilize the enlarged ureter.
  • Take care to preserve the ureteral blood supply, which arises from the aorta, renal artery, gonadal artery, and internal iliac artery, particularly if undertaking extensive tailoring.
  • Tailoring either can be excisional or can involve varied forms of luminal exclusion and ureteral folding; however, reductions smaller than 10F are not recommended to avoid subsequent stenosis.
  • Neocystostomy tunnel lengths of 4:1-6:1 are recommended to avert postoperative reflux.
  • Postoperative drains or splints for the ureters are used at the discretion of the surgeon.


Patients remain on antibiotic prophylaxis for months after surgery, until imaging studies or clinical status warrants discontinuation.

Repeated ultrasonography imaging is mandatory to assess whether hydronephrosis and hydroureter improve after surgery. Because the benefit of repeat VCUG and IVU studies is controversial, in the setting of clinical success and ultrasonography improvement, the only recommendation is that the patient and physician agree on the follow-up regimen.


Surgical complications, as follows, are uncommon and often resolve with observation:

  • Ipsilateral reflux occurs in 2% of patients. Endoscopic ureteral bulking permits a less-invasive management of this complication when the clinical scenario warrants, and it may all but eliminate open reoperation.

  • Contralateral reflux occurs in 10% of patients but resolves within 1 year in nearly all cases.

  • Ureteral obstruction (1%): Early balloon dilation or incision of the meatal stenosis (3 mo) is highly successful. However, strongly consider open reoperation for ureteral stenosis of 1.5 cm or greater and devascularized ureteral segments.

  • Incomplete bladder emptying requiring catheterization (5%): Permanent retention is not reported.

Outcome and Prognosis

Researchers report that surgical outcomes are 98% successful in all major series. Failures were usually in the form of reflux and often occurred with nontapered reimplants. Reoperation with tailoring and repeat neocystostomy is uniformly corrective.

Children who present with infection may experience persistent episodes of UTI. Consider these patients for prolonged prophylaxis to limit the impact of infection on renal growth. Additionally, in female patients of childbearing age, emphasize UTI surveillance during pregnancy.

Kidney function is the key determinant of prognosis because renal dysplasia and infection with associated renal insufficiency are the only expected long-term disabilities associated with primary obstructed megaureter.