INTRODUCTION — Megaureter is defined as a ureter that exceeds the upper limits of normal size. In children, any ureter greater than 7 mm in diameter is considered a megaureter based on measurements in fetuses greater than 30 weeks gestation and children <12 years .
Primary megaureter is a result of a functional or anatomical abnormality involving the ureterovesical junction (figure 1), whereas secondary megaureter results from abnormalities that involve the bladder or urethra (eg, myelomeningocele/neurogenic bladder, prune-belly syndrome, and posterior urethral valves).
Primary megaureter in infants and children will be reviewed here.
CLASSIFICATION — Primary megaureter is classified according to the presence or absence of reflux and obstruction. Management of primary megaureter depends upon the type of megaureter. (See 'Postnatal management' below.)
The types of megaureter are as follows:
●Refluxing, nonobstructed – This common variant is associated with a high grade (ie, grades IV through V) vesicoureteral reflux with a dilated ureter (figure 2) (see "Clinical presentation, diagnosis, and course of primary vesicoureteral reflux", section on 'Grading').
●Refluxing, obstructed – This rare variant is often associated with an ectopic ureter (see "Ectopic ureter").
●Nonrefluxing, nonobstructed – This common variant is also called primary dilated megaureter.
●Nonrefluxing, obstructed – This rare variant is also associated with ectopic ureters and can present with symptoms of pain and a decrease in renal function as identified on prenatal sonographic screening.
EPIDEMIOLOGY — Primary megaureter is the second most common cause of hydronephrosis in the newborn (after ureteropelvic obstruction), accounting for approximately 20 percent of cases. The incidence of primary megaureter is estimated as 0.36 per 1000 live births .
Boys are affected more commonly than girls, and lesions are found more frequently on the left than on the right side [3,4]. The reported rate of bilateral involvement ranges from 30 to 40 percent (image 1) [3,5,6].
PATHOPHYSIOLOGY — The pathogenesis of primary megaureter is uncertain. It appears to be most commonly due to an abnormality or delay in the development of the muscle in the distal ureter adjacent to the ureterovesical junction at 20 weeks gestation . This results in the formation of an aperistaltic segment (movie 1), which leads to functional obstruction. Extremely rarer causes of megaureter include congenital ureteral strictures or ureteral valves.
The refluxing megaureter also has an abnormal ureterovesical (UV) tunnel that allows urine to reflux up the ureter during bladder filling, but more commonly during voiding when the bladder pressure is highest. (See "Clinical presentation, diagnosis, and course of primary vesicoureteral reflux", section on 'Definition and pathogenesis'.)
Antenatal — Primary megaureter usually is detected on antenatal ultrasonography. The ultrasound demonstrates both hydronephrosis and a dilated ureter (>7 mm in diameter) . Affected newborn infants are asymptomatic and typically have a normal physical examination, urinalysis, and serum creatinine.
Postnatal — When the condition is not detected antenatally, children can present at any age after the newborn period with urinary tract infection, hematuria, abdominal pain and/or mass, uremia, or be incidentally diagnosed during evaluation of other conditions. Symptomatic presentation is typically due to an obstructed ureter.
Both renal and nonrenal anomalies can be seen in patients with primary megaureter . Renal and urologic findings include ipsilateral ureteropelvic junction obstruction, contralateral vesicoureteral reflux, and renal hypoplasia/dysplasia. Reported but rare nonrenal findings include ear tags, undescended testes, dermal sinus, tracheomalacia, and aortic aneurysm .
DIAGNOSIS — Ultrasonography confirms the diagnosis of megaureter. If an antenatal diagnosis is made, a postnatal ultrasound is obtained to confirm the presence of megaureter (image 2 and image 3). Although megaureter can occur with or without concomitant dilation of the upper collecting system, it usually presents as hydroureteronephrosis (dilation of both the renal pelvis and ureter). Ureteral tortuosity may be present. In many cases of primary megaureter, there is relatively increased dilation of the distal ureter relative to the proximal ureter or renal collecting system.
Ultrasound examination should be performed after the first two days after birth, preferably at one week of age or later, because hydronephrosis may not be detected due to physiologic volume depletion and relative oliguria. It is important to identify the ureter's origin and insertion into the bladder to help differentiate it from bowel and from an ectopic ureter.
A normal bladder size distinguishes megaureter from lower urinary tract obstruction (eg, posterior urethral valves or prune-belly syndrome), which is characterized by a dilated bladder and/or increased thickness and trabeculation of the bladder wall. The Society of Fetal Urology system can be used to grade the severity of hydronephrosis (image 4), as well as the newer UTD (urinary tract dilation) classification system (figure 3). (See "Fetal hydronephrosis: Etiology and prenatal management", section on 'Definition and grading' and "Fetal hydronephrosis: Etiology and prenatal management", section on 'Prenatal kidney and urologic ultrasound examination'.)
FURTHER EVALUATION — Further evaluation consists of a voiding cystourethrography (VCUG) and possibly diuretic to determine the type of megaureter (eg, refluxing or obstructed), which guides the management approach [9,10]. (See 'Classification' above and 'Postnatal management' below.)
●VCUG – A VCUG must be performed to detect reflux and any evidence of urethral obstruction (eg, posterior urethral valves in males). If severe reflux is present and the ureter drains poorly, the megaureter is likely a refluxing, obstructed type. If no reflux is detected, and the hydronephrosis is severe (Society Fetal Urology [SFU] grade 4 or UTD level 3) then diuretic renography is used to differentiate between the nonrefluxing, obstructed megaureter and the nonrefluxing, nonobstructed type.
●Diuretic renography – Diuretic renography (renal scan and the administration of a diuretic) is used to diagnose urinary tract obstruction (image 5). In our institution, we use 99mTc-mercaptotriglycylglycine (MAG-3 or MAG3) as a radiotracer and lasix as the diuretic (MAG3 lasix renogram). It is performed in patients without reflux and severe hydronephrosis (SFU grade 4 or UTD level 3) or in those with reflux and poor ureter drainage suggestive of a refluxing, obstructed megaureter. It measures the drainage time from the renal pelvis (referred to as washout) and assesses total and each individual kidney's renal function. The washout measurement correlates with the degree of obstruction. In general, a half-life greater than 20 minutes to clear the isotope from the kidney is considered indicative of obstruction. Spontaneous resolution of primary megaureter is less likely in patients with obstructed megaureters. (See 'Asymptomatic patients' below and "Postnatal evaluation and management of hydronephrosis", section on 'Diuretic renography'.)
A more complete description of the diuretic renography is found separately. (See "Postnatal evaluation and management of hydronephrosis", section on 'Diuretic renography'.)
DIFFERENTIAL DIAGNOSIS — Imaging studies differentiate primary megaureter from other causes of hydronephrosis including:
●Ureteropelvic junction obstruction (UPJO) – Ultrasonography that demonstrates dilation of both the renal pelvis and ureter usually differentiates primary megaureter from UPJO. (See "Congenital ureteropelvic junction obstruction", section on 'Diagnosis'.)
●Posterior urethral valves (PUV) – On ultrasound, a normal bladder size helps distinguishes primary megaureter from posterior urethral valves, which is characterized by a dilated bladder and/or increased thickness and trabeculation of the bladder wall, and a dilated posterior urethra (keyhole sign). Voiding cystourethrography (VCUG) is necessary to rule out posterior urethral valves; the dilated and elongated posterior urethra associated with PUV seen on VCUG differentiates this condition from primary megaureter. (See "Clinical presentation and diagnosis of posterior urethral valves", section on 'Diagnosis'.)
●Ureterocele – Ultrasonography differentiates ureterocele from primary megaureter with the detection of a well-defined intravesical mass in the posterior portion of the bladder. (See "Ureterocele", section on 'Diagnosis and evaluation'.)
PRENATAL MANAGEMENT — Unilateral ureterovesical junction (UVJ) obstruction and megaureter have a good prognosis. These fetuses can be followed expectantly in the prenatal period, without intervention or early delivery.
The fetus with bilateral UVJ obstruction should be monitored for oligohydramnios. Expectant routine prenatal management is recommended as long as the amniotic fluid volume remains normal. The antenatal management of hydronephrosis, and the management of pregnancies with severe oligohydramnios are discussed in detail separately. (See "Fetal hydronephrosis: Etiology and prenatal management", section on 'Prenatal management' and "Oligohydramnios: Etiology, diagnosis, and management in singleton gestations", section on 'Prognosis and counseling by etiology'.)
POSTNATAL MANAGEMENT — There are no randomized trials that provide evidence for the optimal management of primary megaureter in infants and children. The following discussion is based upon observational studies, and the experience and opinions of experts in the field. Management options include surgical repair versus conservative medical management. In general, postnatal management decisions are determined by the presence or absence of reflux and/or obstruction.
Surgery — Surgical treatment of the obstructed megaureter consists of excision of the distal obstructive segment, tapering of the dilated ureter, and reimplantation into the bladder using a reflux prevention technique (movie 1). In some cases, a temporary cutaneous ureterostomy is needed to allow for the caliber of the ureter to decrease to a more normal size. The success rate of this procedure, defined as decreased dilation on the ultrasound is greater than 90 percent [11,12].
In a small case series, high pressure balloon dilation appears to be a promising approach to treat primary obstructive megaureter ; however, further studies with a larger number of patients are needed to confirm the long-term effectiveness and safety of this technique.
Medical management — Conservative medical management typically consists of ongoing monitoring and antibiotic prophylaxis . These patients are followed by annual renal ultrasonography to monitor renal growth and hydroureteronephrosis. Antibiotic prophylaxis is usually prescribed until the patient is toilet trained.
Antibiotic prophylaxis — Historically, all patients with megaureter received oral antibiotic prophylaxis (amoxicillin, 12 to 25 mg/kg per day or trimethoprim-sulfamethoxazole, 2 mg/kg per day) because of the high risk of development of infection due to urinary stasis . In most published case series, antibiotic prophylaxis was given routinely through the first one to two years of life [3,4,6]. As a result, there are no data demonstrating that prophylaxis is beneficial in patients with megaureter. However, until studies show that antibiotic prophylaxis is not indicated, it seems prudent, especially in severe cases of megaureter, to continue to administer antibiotic prophylaxis until the patient is toilet trained because of the increased risk of urinary tract infection. (See 'Our approach' below.)
Nonrefluxing megaureter — In nonrefluxing megaureter, the choice between surgery and medical management is based on the presence of signs and symptoms and evidence of impaired renal function.
Asymptomatic patients — In the asymptomatic patient with nonrefluxing megaureter and normal renal function based on diuretic renography, initial nonoperative medical management is warranted because, in most cases, hydroureteronephrosis resolves spontaneously without renal function impairment (image 5) [3,5,6,9,10,14]. Even severe hydroureteronephrosis, in some cases, can resolve spontaneously, although the time for resolution is longer [3-5]. Several studies have reported subsequent surgical correction in approximately 15 to 20 percent of cases without reflux because of new-onset of symptoms or renal function deterioration due to increasing obstruction in patients in whom there is no resolution [3,4,14].
Based upon the currently available data, asymptomatic patients with nonrefluxing, nonobstructed megaureters can be managed medically with close monitoring. Surgical correction should be performed in patients with obstructed lesions. In patients who are initially managed conservatively, if hydronephrosis increases, renal function on the affected side decreases, or symptoms develop, surgical repair is indicated because it is likely that clinically significant obstruction is present (picture 1). Surgical correction of obstructed megaureters improves renal drainage, as detected by a reduction in hydroureteronephrosis on ultrasound [11,12].
This approach is supported by the following case series [4,15]:
●In a study of 49 patients, spontaneous resolution occurred in 80 percent of nonobstructive, nonrefluxing megaureter, but only 20 percent in those who demonstrated an obstructive or partial obstructive diuretic renographic pattern . Of the 16 patients with an obstructive or partially obstructive lesion, nine underwent surgical correction. The long-term renal outcome was excellent except for in those who already had renal abnormalities (eg, renal hypoplasia and dysplasia) and decreased renal function detected during the neonatal period.
●In a second case series of 75 patients with primary megaureter diagnosed between 1990 and 2005, surgical repair was performed on 34 of 88 primary ureters because of symptomatic disease or decreased renal function associated with massive dilation and obstruction . Of the remaining patients who were managed conservatively with observation, subsequent complete resolution was documented in 47 of the remaining 54 ureters (87 percent). In this cohort, multivariate analysis showed that perinatal presentation and a nonobstructive pattern on diuretic renography were associated with spontaneous resolution. In contrast, the grade of hydronephrosis was not predictive of spontaneous resolution.
Symptomatic patients — Surgical correction is needed in a child with nonrefluxing megaureter who presents with recurrent urinary tract infection, pyelonephritis, persistent flank pain, calculi, or hematuria. Symptoms resolve after surgical correction.
Refluxing megaureter — Patients with refluxing, nonobstructed megaureter have moderate to severe vesicoureteral reflux (eg, grade IV to V vesicoureteral reflux). The management of these patients is discussed elsewhere in the program. (See "Management of vesicoureteral reflux", section on 'Grades III to V'.)
Patients with refluxing, obstructed megaureter often have ectopic ureters that enter into the bladder, neck, or urethra. They are typically managed with surgery, using a similar approach of those with an ectopic ureter, which is discussed separately. (See "Ectopic ureter", section on 'Management'.)
Prenatal presentation — Our management approach is based upon the presence or absence of reflux, and/or obstruction as detected by imaging studies. Postnatal ultrasonography after the first week of life is performed to confirm the diagnosis of primary megaureter with unilateral megaureter, and within 24 to 72 hours for those with bilateral involvement. In patients with megaureter, voiding cystourethrogram is performed to detect the presence or absence of vesicoureteral reflux (VUR). Diuretic renography is performed in infants without VUR and severe hydronephrosis (SFO grade 4 or UTD level 3), or with VUR and poor ureteral drainage, to determine the presence or absence of obstruction. (See 'Diagnosis' above.)
The following management approach is based on the results of the above imaging studies:
●Nonobstructive, nonrefluxing megaureter – Patients with nonobstructive, nonrefluxing megaureter are managed nonoperatively. These patients are followed by annual renal ultrasonography to monitor renal growth and hydroureteronephrosis. Antibiotic prophylaxis is prescribed for more severe cases until the patient is toilet trained.
•If the megaureter remains stable, sonogram evaluation continues at longer intervals (yearly until age three to five, then every other year, and once every five years in adolescence) until resolution.
•If the megaureter and/or hydronephrosis worsens, a diuretic renogram is performed to assess overall renal function and possible obstruction. A >10 percent decrease in renal function is an indication for surgery.
•Surgical intervention is performed in patients who develop symptoms, calculi, recurrent infection, hematuria, or a decrease in the function of the affected kidney.
●Refluxing, nonobstructed megaureter – The management choices of patients with high-grade VUR (ie, grades III to V) include medical management with ongoing monitoring and prophylactic antibiotics, or surgical correction. These options are discussed separately. (See "Management of vesicoureteral reflux", section on 'Grades III to V'.)
●Obstructed megaureter – Surgical intervention is indicated in patients with obstructed lesions documented by increasing hydroureteronephrosis and/or the presence of a prolonged diuretic renographic drainage pattern.
Postnatal presentation — We recommend surgical correction for any symptomatic patient with primary megaureter (movie 1). The management for asymptomatic patients who are diagnosed as an incidental finding on abdominal imaging is similar to that of patients who are diagnosed prenatally, and is dependent upon the presence of reflux and/or obstruction.
OUTCOME — The long-term outcome of primary megaureter is generally excellent [4,10].
●As noted above, most cases of nonobstructive, nonrefluxing megaureter will spontaneously resolve (image 5). (See 'Nonrefluxing megaureter' above.)
●The outcome of surgical correction for obstructed lesions is excellent with success rates greater than 90 percent (picture 1). (See 'Surgery' above.)
●Outcome for either medical or surgical management of refluxing megaureter (ie, grade III to V vesicoureteral reflux) is also excellent. (See "Clinical presentation, diagnosis, and course of primary vesicoureteral reflux", section on 'Natural history' and "Clinical presentation, diagnosis, and course of primary vesicoureteral reflux", section on 'Kidney scarring' and "Management of vesicoureteral reflux".)
●Poor renal outcome appears to be due to the concomitant presence of congenital renal abnormalities (eg, renal hypoplasia and dysplasia) rather than as a consequence of primary megaureter, except in the setting of high-grade or worsening obstruction .
SUMMARY AND RECOMMENDATIONS
●Introduction and classification – Primary megaureter is defined as a ureter that is >7 mm in diameter and is caused by a functional or anatomical abnormality, which involves the ureterovesical junction (UVJ). It is classified into four types based upon the presence of reflux or obstruction. (See 'Introduction' above and 'Classification' above.)
●Epidemiology – Primary megaureter is the second most common cause of hydronephrosis in the newborn (after ureteropelvic junction obstruction), accounting for approximately 20 percent of cases, with an estimated incidence of 0.36 per 1000 live births. (See 'Epidemiology' above.)
●Pathophysiology – Although the pathogenesis is uncertain, it appears that primary megaureter is usually due to an abnormality or delay in the development of the muscle in the distal fetal ureter at 20 weeks gestation. (See 'Pathophysiology' above.)
●Clinical presentation – Primary megaureter usually presents prenatally as a consequence of antenatal sonography. Postnatal presentation can occur at any age with symptoms due to urinary tract infection, hematuria, abdominal pain and/or mass, or uremia. (See 'Clinical presentation' above.)
●Diagnosis – The diagnosis of primary megaureter is made by ultrasonography that demonstrates both hydronephrosis and a dilated ureter (hydroureteronephrosis). (See 'Diagnosis' above.)
●Further evaluation – After the diagnosis of megaureter is made, further evaluation determines the type of megaureter (eg, refluxing, obstructed), which guides management. (See 'Further evaluation' above.)
•Voiding cystourethrography (VCUG) is performed in all patients with megaureters to detect the presence or absence of vesicoureteral reflux (VUR).
•Diuretic renography (renal scan and the administration of a diuretic) is used to detect urinary tract obstruction. It is performed in cases with severe hydronephrosis or those with reflux and poor ureter drainage noted on VCUG.
●Differential diagnosis – Imaging studies differentiate primary megaureter from other causes of hydronephrosis, including ureteropelvic junction obstruction, posterior urethral valves, and ureterocele. (See 'Differential diagnosis' above.)
●Management – There are no randomized trials that provide evidence for the optimal management of primary megaureter. The following management regimen is based upon observational studies, and the experience and opinions of the author.
•We suggest not performing prenatal intervention or early delivery in fetuses with megaureter (Grade 2C). (See 'Prenatal management' above.)
•In symptomatic patients with any type of megaureter, we suggest surgical intervention to relieve the obstruction (movie 1) (Grade 2C). (See 'Our approach' above.)
•In asymptomatic patients with nonrefluxing, nonobstructed megaureters (image 5), we suggest nonoperative management (Grade 2C). This includes monitoring with annual ultrasounds and prophylactic antibiotics until the patient is toilet trained. Surgery is indicated if there is subsequent development of symptoms, or evidence of obstruction or impaired renal function. (See 'Nonrefluxing megaureter' above and 'Our approach' above.)
•In asymptomatic patients with obstructed megaureter (picture 1), we suggest surgical correction (Grade 2C). (See 'Our approach' above.)
•In asymptomatic patients with refluxing, nonobstructed megaureters, we suggest either medical treatment with prophylactic antibiotics and ongoing monitoring, or surgical correction (Grade 2C). (See "Management of vesicoureteral reflux".)
3 : Rate and predictors of spontaneous resolution of prenatally diagnosed primary nonrefluxing megaureter.
5 : The fate of prenatally diagnosed primary nonrefluxing megaureter: do we have reliable predictors for spontaneous resolution?
7 : Segmental up-regulation of transforming growth factor-beta in the pathogenesis of primary megaureter. An immunocytochemical study.
8 : British Association of Paediatric Urologists consensus statement on the management of the primary obstructive megaureter.
12 : Radiographic changes following excisional tapering and reimplantation of megaureters in childhood: long-term outcome in 46 renal units.
13 : High pressure balloon dilation of the ureterovesical junction--first line approach to treat primary obstructive megaureter?
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