Solitary Ectopic Ureter

Abstract

The termination of the normal ureter is in the posterior bladder wall at the superior lateral margin of the trigone. An ectopic ureter inserts more medially and caudally in the bladder, urethra, or genital tract. Usually, ectopic ureters drain the upper portion of a double system. Rarely, however, an unduplicated ureter draining an entire kidney terminates ectopically. The embryology and clinical and radiographic features of solitary ectopic ureters will be discussed below. Embryology (4) The ureters arise as medial buds from the caudal ends of the paired wolffian ducts. They rotate into a posterolateral direction as they grow cephalad into the metanephric blastoderm or future renal cortex (Fig. 1, A). By a series of divisions of their proximal ends, the renal pelves, major and minor calyces, and distal collecting tubules are formed. The distal ends of the ureters as well as their parent structures, the wolffian ducts, are incorporated into the formation of the bladder trigone. Thus, the ureters gain their independent openings in the bladder lateral to each associated wolffian duct opening (Fig. 2, A). The wolffian ducts continue their caudad migration, and the duct openings begin to approach each other in the midline. This downward migration ends at the miillerian tubercle or future verumontanum in the posterior urogenital sinus. Consequently, elements of the distal wolffian ducts contribute to the formation of the trigone and posterior wall of the proximal urethra (pars prostatica urethralis) (Fig. 2, B). In the male, the wolffian ducts give off another set of terminal buds, the seminal vesicles, and persist as the vasa deferentes. In the female, their distal portions may persist as Gartner's ducts. Where a wolffian duct has given off two ureteric buds, a double collecting system will be present (Fig. 1, B). Since the accessory ureteric bud arose cephalad to the first or primary one, it will form the upper collecting system; it also will maintain its connection to the parent wolffian duct for a longer period of time, and as these ducts are drawn into the developing trigone, the accessory ureter will be carried along and eventually will open in a lower and more central position. The more cephalad the rise of the ureteric bud from the wolffian duct, the later it will terminate in the bladder and the more likely this termination will be extravesical in the urethra. This is true for both accessory and primary ureters. Should this event occur in case of a primary ureter only, then the ipsilateral hemitrigone will be absent and the nonduplicated ectopic ureter will terminate in the posterior urethra (Fig. 3). Clinical and Radiographic Features From 10 to 30 per cent of all ectopic implantations of ureters are associated with a nonduplicated collecting system (2, 3). In addition to 2 cases to be discussed, there have been 21 reported instances of bilateral ectopia of nonduplicated ureters (1).