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:
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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.
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Ureteral valves, membranes, and polyps demonstrate intrinsic filling defects that differentiate these lesions from primary megaureter. These lesions are rare.
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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:
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Contralateral renal agenesis (9%-15%)
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Microcystitis in bilateral lesions
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Contralateral ureteroceles
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Renal dysplasia
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]
Pathophysiology
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.
Etiology
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]
Epidemiology
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]
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This renal sonogram demonstrates hydronephrosis with good parenchymal thickness and retained corticomedullary differentiation.
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This pelvic sonogram reveals the classic spindle configuration of primary obstructed megaureter.
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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.)
