Obstructed Megaureter

Updated: Dec 26, 2016
  • Author: Robert A Mevorach, MD; Chief Editor: Edward David Kim, MD, FACS  more...
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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.


History of the Procedure

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]

Obstructive megaureter is, in itself, a misnomer because most cases demonstrate 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.



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.




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 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]



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.



Children with an obstructed megaureter may present with vague abdominal pain, hematuria, UTI, fever of unknown origin, or an abdominal mass. The primary presentation, antenatal hydronephrosis, is diagnosed with prenatal ultrasonography.

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

  • UTI

  • Hematuria

  • Pyuria

  • Flank mass

  • Fever of unknown origin

  • Abdominal or pelvic pain

  • Abdominal mass

  • Serendipitous identification on imaging (eg, ultrasonography; CT scanning; kidneys, ureters, and bladder [KUB] radiography; bone scan)



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 are not obstructed to 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.


Relevant Anatomy

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 the single and the duplicated collecting systems, it is associated most commonly with a single system.

  • 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.



In mild cases of obstructed megaureter, surgery may be unnecessary. Physicians may monitor symptoms, perform periodic radiologic imaging, and administer antibiotic prophylaxis.

Document that patients are free of infection at the time of reconstruction.