Megaureter

Megaureter is defined as ureter > 7 mm in diamater and account for 10% of infants with prenatally diagnosed ureteral abnormalities.

Megaureters can be classified as primary or secondary types with subclassifications defined based on the presence of reflux and obstruction. Primary megaureter has been associated with contralateral vesicoureteral reflux, contralateral renal agenesis, contralateral ureteroceles, renal dysplasia, and ureteral duplications.

• Primary obstructed nonrefluxing megaureter: Due to stenotic, aperistaltic segment of distal ureter at the level of the ureterovesical junction. The normal ureter proximal to the aperistaltic segment dilates because of relative obstruction. Analogous to achalasia and Hirschsprung disease, but ganglion cell issues have not been found. Intervention is indicated in those with progressive hydronephrosis, parenchymal loss, and recurrent infections.
• Secondary obstructed nonrefluxing megaureter: Due to neurogenic bladder, obstructing ureterocele, or bladder mass.
• Primary refluxing megaureter: Due to inadequate ureteral tunnel length at the ureterovesical junction and may be obstructed or nonobstructed. More commonly bilateral. Intervention indicated in those with recurrent infections and those with a fixed ureteral orifice abnormality resulting in high-grade reflux.
• Secondary refluxing megaureter: Due to abnormalities of the bladder or urethra (e.g., neurogenic bladder, posterior urethral valves, or ureterocele).
• Primary or secondary nonrefluxing nonobstructed megaureter: Diagnosis of exclusion.

References

• Berrocal T, López-Pereira P, Arjonilla A, Gutiérrez J. Anomalies of the distal ureter, bladder, and urethra in children: embryologic, radiologic, and pathologic features. Radiographics. 2002 Sep-Oct;22(5):1139-64.
• Mevorach RA. Obstructed Megaureter. eMedicine
• Rudolph's Pediatrics - 21st Ed. (2003)
• Vargas B, Lebowitz RL. The coexistence of congenital megacalyces and primary megaureter. AJR Am J Roentgenol. 1986 Aug;147(2):313-6.