Ureteral abnormalities represent a complex and often confusing subset of urologic anomalies that manifest in many ways. However, in the current era, hydronephrosis that is evident on fetal ultrasonography often heralds a ureteral abnormality.
Ureteral duplication is the most common renal abnormality, occurring in approximately 1% of the population and 10% of children who are diagnosed with urinary tract infections (UTIs). Incomplete ureteral duplication, in which one common ureter enters the bladder, is rarely clinically significant. Alternatively, complete ureteral duplication, in which two ureters ipsilaterally enter the bladder, has a propensity for vesicoureteral reflux (VUR) into the lower pole and obstruction of the upper pole, which can be problematic.
The upper-pole ureter may be ectopic in its insertion into the bladder or may end in a ureterocele. Both conditions are more common in duplicated collecting systems but may also be seen in single systems.
A ureterocele is a cystic dilatation of the terminal intravesical ureter. Ureteroceles that are entirely contained within the bladder are considered intravesical. A ureterocele is considered ectopic if any portion is permanently situated at the bladder neck or the urethra, regardless of the position of the orifice.
A solitary collecting system is referred to as a single-system ureterocele. The orifice of a ureterocele may be stenotic, normal in size, or, occasionally, patulous. It may be located intravesically or extravesically. Ureteroceles widely vary in size, from ones that are difficult to visualize to ones that fill the entire bladder. Ureteroceles can often be obstructive if the orifice is stenotic or ectopically located and can also reflux if poorly supported with a gaping orifice.
With appropriate management, the ultimate prognosis of duplicated ureter, ureteral ectopia, or ureterocele is excellent.
Ureteral embryology is fundamental in understanding abnormal development of the ureter. Ureteral development begins as early as 4 weeks' gestation. The ureteral bud branches off of the mesonephric (or Wolffian) duct and eventually extends into the nephrogenic blastema, an area of undifferentiated mesenchyma. The ureteral bud is responsible for the formation of the entire renal collecting system, from the ureteral orifice to the collecting ducts of the kidney.
At the distal aspect of the ureteral bud, the mesonephric duct is incorporated into the developing bladder, and the ureteral orifice is superolaterally carried to its normal position on the trigone. The more distal segment of the mesonephric duct is carried inferomedially and is incorporated into the bladder neck. In the male fetus, it also develops into the seminal vesicle, vas deferens, and epididymis. In females, it becomes the Gartner duct, which is located between the vagina and urethra.
In cases of ureteral duplication where the ureteral bud arises twice, the lower-pole ureter integrates with the bladder earlier than expected and, as a result, is carried into a more superolateral position. Thus, the distal ureter is poorly supported by the trigone and has a shorter intramural tunnel, both of which situations increase the likelihood of VUR. The upper-pole ureter then integrates with the bladder later than usual and is inferomedially carried. This may result in a ureteral orifice that is low on the trigone or is ectopically located at the bladder neck, ejaculatory duct, seminal vesicle, or vas deferens in males.
In females, the ureter may end in a Gartner duct, which can eventually erode into the nearby vagina or the urethra, inferior to the urinary sphincter. This may be the cause of continuous urinary incontinence in females. In boys, all of the Wolffian structures are located above the external urinary sphincter, and incontinence does not occur.
Ureteral ectopia can occur without duplication and is believed to result from the delayed incorporation of the distal ureter into the developing bladder, as described above.
The embryology of the ureterocele is debatable. Some believe that failure of the Chwalla membrane to break down at the distal ureter during development results in obstruction and saccular dilation. Others argue that aberrant signaling from the expanding urogenital sinus results in dilation of the distal ureter.
United States statistics
In autopsy series, the incidence of ureteral duplication is estimated at slightly less than 1%. In studies of young children with UTIs, the incidence of duplication rises to 8%. The incidence of ureteroceles has been reported to be in the range of 1 per 5,000-12,000 population. Approximately 10% are bilateral, 60-80% are ectopic, and 80% are associated with an upper-pole ureter of a duplex kidney. Single-system ectopic ureteroceles are rare, usually occur in males, and may be associated, in rare cases, with cardiac and genital anomalies. When ureteroceles arise from the upper pole of a duplicated kidney, the upper pole is frequently dysplastic.
Prenatally, ureteral duplication is commonly suggested by hydronephrosis when the upper-pole ureter is associated with obstruction or when the lower pole is associated with high-grade reflux. The duplication may present in early childhood or later in life, when UTI prompts evaluation.
Prenatally, ureteral ectopia is commonly detected when hydronephrosis is present because of obstruction. Ectopic ureters that enter below the urethral sphincter present at school age or later in girls who have failed to toilet train or who have had continuous drip incontinence.
Prenatally, ureteroceles are most commonly diagnosed when associated with hydronephrosis or in childhood when associated with UTI. When found in adults, they are usually intravesical, are associated with a single collecting system, are less likely to alter the function of the involved kidney, and may not be of clinical concern.
Ureteral duplication, ectopia, and ureteroceles are all more common in females. This may reflect the higher likelihood of UTIs in females, resulting in subsequent detection of the duplication.
Ureteroceles are more common in whites than in blacks.