Ahmad H. Bani-Hani, MD, FAAP, FACS
BASICS
DESCRIPTION
• Megaureter is a ureter that is dilated out of proportion to the rest of the urinary tract
• Most consider ureters measuring ≥7 mm in diameter by ultrasound a megaureter
• Four types of megaureter are described:
– Refluxing megaureter
– Obstructed megaureter
– Refluxing and obstructed megaureter
– Nonrefluxing-nonobstructed megaureter
• Each of the above groups further categorized as either primary (defect lies in the ureter itself) or secondary (another disorder leading to megaureter such as urethral obstruction)
• Primary megaureter represents the 2nd most common cause of hydronephrosis in the newborn, with ureteropelvic junction obstruction the most common cause
EPIDEMIOLOGY
Incidence
• Varies depending on etiology
– Vesicoureteral reflux (VUR): 0.4–1.8% in children
– Primary obstructive megaureter (POM): 1 per 10,000 population
– VUR is more common in females
– POM is more common in males with predilection for the left kidney
– Bilateral involvement in up to 40%
Prevalence
N/A
RISK FACTORS
• Posterior urethral valves
• Neurogenic bladder
• Diabetes insipidus
Genetics
• No specific genetic factors can be identified in the majority of patients with megaureters
• VUR can be familial
PATHOPHYSIOLOGY
• Refluxing megaureters
– Caused by congenital abnormality of the intravesical ureter secondary to abnormal insertion of the ureter into the bladder or the intravesical portion of the ureter is not long enough to enable closure of the ureter during bladder filling
• POM:
– Exact etiology is unclear, however, the most common finding is a distal adynamic ureteral segment that affects the free efflux of urine resulting in a functional obstruction
• Refluxing, obstructed megaureter:
– This paradox of pathology was 1st reported by Weiss and Lytton. The muscle cells in the intravesical and juxtavesical sections of the distal ureter are so lacking that they become incapable of adequate transmission of urine. On VCUG, delayed emptying of the refluxing contrast/sharp cut-off distally is highly suggestive of the diagnosis
• Nonrefluxing, nonobstructed megaureter
– Transient dilatation of the ureter and/or renal pelvis. Renal parenchyma is preserved. Can be primary (idiopathic) or secondary to urosepsis (bacterial toxins can paralyze the ureteral muscle and produce atonic ureter) or polyuric kidney that lost its concentration ability, eg, following ablation of posterior urethral valves
ASSOCIATED CONDITIONS
• Posterior urethral valves
• Prune belly syndrome
DIAGNOSIS
HISTORY
• Most megaureters are diagnosed currently prenatally with ultrasound (asymptomatic)
• For late diagnosis, patients may present with abdominal pain, UTIs, or kidney stones
PHYSICAL EXAM
• Abdominal mass
• Abdominal pain and costovertebral angle tenderness with pyelonephritis
DIAGNOSTIC TESTS & INTERPRETATION
Lab
• Urine analysis and culture if UTI is suspected
• Serum electrolytes, BUN, and creatinine
• C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) for pyelonephritis
Imaging
• Normally best to perform ultrasound imaging several days after birth to allow relative newborn dehydration to equilibrate
• Renal and bladder ultrasound:
– Establishes the diagnosis of megaureter, assesses renal parenchyma and may provide clues on possible etiology eg, thickened bladder wall secondary to urethral valves
• Voiding cystourethrogram:
– Will evaluate for the presence of VUR and urethral abnormalities such as anterior or posterior urethral valves
• Diuretic renal scan:
– 99mTc-mercaptotriglycylglycine (MAG-3 scan)
– Assesses renal function and presence of obstruction to the flow of urine
– Furosemide washout correlates with the degree of obstruction
– In general, a washout of >20 min after furosemide suggests obstruction
Diagnostic Procedures/Surgery
• Whitaker test (perfusion-pressure test):
– More invasive as it requires percutaneous renal access
– Will provide valuable information if the diuretic renal scan is equivocal
• Endoscopy: Invasive test as it requires anesthesia. Can be combined with transurethral resection of urethral valves if present
Pathologic Findings
• Varies with etiology
• With electron microscopy, the muscle population and the size of smooth muscle cells of megaureters can be measured
– In obstructed megaureters, muscle hypertrophy and hyperplasia are expected. These changes are absent or minimal in refluxing megaureters and ureters associated with prune belly syndrome
– Collagen fiber derangements can also be seen in primary obstructed megaureter (Increased collagen types I and III deposition)
DIFFERENTIAL DIAGNOSIS
• Bowel segment misinterpreted as dilated ureter
• Posterior/anterior urethral valves
• Prune belly syndrome
• Retrocaval/retroiliac ureter
• Ureteral stone
• Ureterocele
• Ureterovesical junction obstruction
• VUR
TREATMENT
GENERAL MEASURES
• Serial renal and bladder ultrasounds to monitor progress/resolution of megaureter is important
• Workup of megaureter to assess the presence or absence of reflux and/or obstruction will guide further treatment options
• Prenatally discovered megaureter
– Unilateral obstructed megaureter has a good prognosis
These patients can be followed expectantly in the prenatal period, without further intervention or early delivery
Bilaterally obstructed megaureter findings require close monitoring for the development of oligohydramnios
MEDICATION
First Line
• Treat active UTI with culture appropriate antibiotics
• Consider prophylactic antibiotics in refluxing and obstructed megaureter variants (eg, Amoxicillin)
Second Line
N/A
SURGERY/OTHER PROCEDURES
• Refluxing megaureters:
– Antibiotic prophylaxis and monitor progress with renal ultrasound (RUS) and VCUG
– Ureteral reimplant in cases of breakthrough UTIs, renal scarring, or noncompliance with medications
• Primary obstructed megaureter (1)[A]:
– Excision of the distal adynamic ureteral segment and ureteral reimplant. Ureteral tapering maybe required
• Refluxing, obstructed megaureter:
– Excision of the distal ureteral segment and ureteral reimplant. Often requires ureteral tapering
• Nonrefluxing, nonobstructed megaureter: Observation with serial ultrasound is all that is needed
ADDITIONAL TREATMENT
Radiation Therapy
N/A
Additional Therapies
N/A
Complementary & Alternative Therapies
• If the child is newborn or infant, temporizing the obstructing variant of megaureter can be achieved with:
– Ureteral stent insertion
– Cutaneous ureterostomy
ONGOING CARE
PROGNOSIS
• Depends on the baseline renal function (2)[A]
• Surgical correction of obstructing megaureters carries a high success rate
• Most nonobstructive, nonrefluxing megaureters will resolve with time
• Outcomes can be poor with concomitant renal anomalies such as renal hypoplasia and dysplasia
COMPLICATIONS
• UTIs
• Ureteral obstruction, mainly technical inattention to details during ureteral reimplant that will cause either:
– Ureteral kinking at the bladder insertion site
– Compromised blood supply to the distal ureter associated with excisional ureteral tapering
• Nephrolithiasis
FOLLOW-UP
Patient Monitoring
• Serial RUS (3)[A]
• Serial serum chemistry to monitor renal function
Patient Resources
Urology Care Foundation http://www.urologyhealth.org/urology/index.cfm?article=3
REFERENCES
1. Stehr M, Metzger R, Schuster T, et al. Management of the primary obstructed megaureter (POM) and indication for operative treatment. Eur J Pediatric Surg. 2002;12(1):32–37.
2. Liu HY, Dhillon HK, Yeung CK, et al. Clinical outcome and management of prenatally diagnosed primary megaureters. J Urol. 1994;152:614–617.
3. Shukla AR, Cooper J, Patel RP, et al. Prenatally detected primary megaureter: A role for extended follow-up. J Urol. 2005;173(4):1353–1356.
ADDITIONAL READING
Di Renzo D, Aguiar L, Cascini V, et al. Long-term followup of primary nonrefluxing megaureter. J Urol. 2013;190:1021–1026.
See Also (Topic, Algorithm, Media)
• Hydronephrosis/Hydroureteronephrosis, (Dilated Ureter/Renal Pelvis), Pediatric
• Hydronephrosis/Hydroureteronephrosis, (Dilated Ureter/Renal Pelvis), Prenatal
• Megaureter, Congenital Image 
• Posterior Urethral Valves
• Prune Belly Syndrome
• Vesicoureteral Reflux
CODES
ICD9
753.22 Congenital obstruction of ureterovesical junction
ICD10
Q62.2 Congenital megaureter
CLINICAL/SURGICAL PEARLS
• Wide spread use of prenatal ultrasound helps identify patients with megaureters at an early stage, commonly prenatally.
• It is important to classify megaureters based on their refluxing and/or obstructing status with the aid of VCUG and diuretic renal scan.
• Long-term follow-up in patients with megaureter is important for best outcome.