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. 
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. 
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. 
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:
Fever of unknown origin
Abdominal or pelvic pain
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:
Contralateral renal agenesis (9%-15%)
Microcystitis in bilateral lesions
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.
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.
Johnston JH, Farkas A. The congenital refluxing megaureter: experiences with surgical reconstruction. Br J Urol. 1975 Apr. 47 (2):153-9. [Medline].
Hendren WH, Henderson BM. Recent advances in pediatric surgery. Am J Surg. 1969 Sep. 118(3):338-55. [Medline].
Creevy CD. The atonic distal ureteral segment (ureteral achalasia). J Urol. 1967 Mar. 97(3):457-63. [Medline].
Williams DI, Hulme-Moir I. Primary obstructive mega-ureter. Br J Urol. 1970 Apr. 42(2):140-9. [Medline].
McLaughlin AP 3rd, Pfister RC, Leadbetter WF, Salzstein SL, Kessler WO. The pathophysiology of primary megaloureter. J Urol. 1973 May. 109(5):805-11. [Medline].
Mortell A, Fourcade L, Solari V, Puri P. Bilateral megaureters in the Adriamycin rat model. Pediatr Surg Int. 2005 Mar. 21(3):212-6. [Medline].
Patti G, Menghini ML, Todini AR, Marrocco G, Calisti A. The role of the renal resistive index ratio in diagnosing obstruction and in the follow-up of children with unilateral hydronephrosis. BJU Int. 2000 Feb. 85(3):308-12. [Medline].
DeFoor W, Minevich E, Reddy P, Polsky E, McGregor A, Wacksman J, et al. Results of tapered ureteral reimplantation for primary megaureter: extravesical versus intravesical approach. J Urol. 2004 Oct. 172(4 Pt 2):1640-3; discussion 1643. [Medline].
Lee SD, Akbal C, Kaefer M. Refluxing ureteral reimplant as temporary treatment of obstructive megaureter in neonate and infant. J Urol. 2005 Apr. 173(4):1357-60; discussion 1360. [Medline].
Rabinowitz R, Barkin M, Schillinger JF, Jeffs RD. Surgical treatment of the massively dilated primary megaureter in children. Br J Urol. 1979 Feb. 51(1):19-23. [Medline].
Babu R. ‘Mini reimplantation’ for the management of primary obstructed megaureter. J Pediatr Urol. 2016 Apr. 12 (2):103.e1-4. [Medline].
Kajbafzadeh AM, Payabvash S, Salmasi AH, Arshadi H, Hashemi SM, Arabian S, et al. Endoureterotomy for treatment of primary obstructive megaureter in children. J Endourol. 2007 Jul. 21(7):743-9. [Medline].
Tatlisen A, Ekmekçioglu O. Direct nipple ureteroneocystostomy in adults with primary obstructed megaureter. J Urol. 2005 Mar. 173(3):877-80. [Medline].
Arena F, Baldari S, Proietto F, Centorrino A, Scalfari G, Romeo G. Conservative treatment in primary neonatal megaureter. Eur J Pediatr Surg. 1998 Dec. 8(6):347-51. [Medline].
Bakker HH, Scholtmeijer RJ, Klopper PJ. Comparison of 2 different tapering techniques in megaureters. J Urol. 1988 Nov. 140(5 Pt 2):1237-9. [Medline].
Bapat S, Bapat M, Kirpekar D. Endoureterotomy for congenital primary obstructive megaureter: preliminary report. J Endourol. 2000 Apr. 14(3):263-7. [Medline].
Belman AB. Megaureter. Classification, etiology, and management. Urol Clin North Am. 1974 Oct. 1(3):497-513. [Medline].
Erbas B, Royal SA, Joseph D. Scintigraphic evaluation of obstructing primary megaureter with Tc-99m MAG3. Clin Nucl Med. 1997 Jun. 22(6):355-8. [Medline].
Lockhart JL, Politano VA. Management of massively dilated ureters in children. Urology. 1981 Sep. 18(3):229-34. [Medline].
Payabvash S, Kajbafzadeh AM, Tavangar SM, Monajemzadeh M, Sadeghi Z. Myocyte apoptosis in primary obstructive megaureters: the role of decreased vascular and neural supply. J Urol. 2007 Jul. 178(1):259-64; discussion 264. [Medline].
Rabinowitz R, Barkin M, Schillinger JF, Jeffs RD, Cook GT. The influence of etiology on the surgical management and prognosis of the massively dilated ureter in children. J Urol. 1978 Jun. 119(6):808-13. [Medline].
Shukla AR, Cooper J, Patel RP, Carr MC, Canning DA, Zderic SA, et al. Prenatally detected primary megaureter: a role for extended followup. J Urol. 2005 Apr. 173(4):1353-6. [Medline].
Stehr M, Metzger R, Schuster T, Porn U, Dietz HG. Management of the primary obstructed megaureter (POM) and indication for operative treatment. Eur J Pediatr Surg. 2002 Feb. 12(1):32-7. [Medline].
Thompson A, Gough DC. The use of renal scintigraphy in assessing the potential for recovery in the obstructed renal tract in children. BJU Int. 2001 Jun. 87(9):853-6. [Medline].
Robert A Mevorach, MD Associate Professor, Departments of Urology and Pediatrics, University of Rochester School of Medicine
Disclosure: Nothing to disclose.
Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference
Disclosure: Received salary from Medscape for employment. for: Medscape.
Edward David Kim, MD, FACS Professor of Surgery, Division of Urology, University of Tennessee Graduate School of Medicine; Consulting Staff, University of Tennessee Medical Center
Edward David Kim, MD, FACS is a member of the following medical societies: American College of Surgeons, American Society for Reproductive Medicine, American Society of Andrology, American Urological Association, Sexual Medicine Society of North America, Tennessee Medical Association
Disclosure: Serve(d) as a speaker or a member of a speakers bureau for: Endo, Avadel.
Bradley Fields Schwartz, DO, FACS Professor of Urology, Director, Center for Laparoscopy and Endourology, Department of Surgery, Southern Illinois University School of Medicine
Bradley Fields Schwartz, DO, FACS is a member of the following medical societies: American College of Surgeons, American Urological Association, Association of Military Osteopathic Physicians and Surgeons, Endourological Society, Society of Laparoendoscopic Surgeons, Society of University Urologists
Disclosure: Serve(d) as a speaker or a member of a speakers bureau for: Cook Medical; Olympus.
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