ECTOPIC URETER
An ectopic ureter terminates caudal to the normal position in the
trigone. Although a ureter that terminates cranial to the normal position is
clearly abnormal, and is often associated with vesicoureteral reflux (see Plate
2-21), the term “ectopic” is generally not applied.
In males, the most common sites of
ureteral ectopia are the prostatic urethra and seminal glands (vesicles),
whereas in females, the most common sites are the urethra and vagina. The
incidence of ectopic ureter is not known with precision, although one series
estimated it at 1 in 1900. The condition is at least twice as common in females
than in males, for unknown reasons.
Pathogenesis
As described on page 30, the ureteric
buds appear toward the caudal ends of the mesonephric ducts during the fifth
week of gestation. Each ureteric bud grows into the adjacent mass of
metanephric mesenchyme, the precursor of the kidney, to form a ureter, a
pyelocalyceal system, and collecting ducts.
During the sixth week, each
mesonephric duct undergoes a process known as exstrophy, in which its most
caudal end everts into the primitive bladder and draws in the attached ureter.
After the ureters enter the bladder, they separate from the mesonephric duct
and attach to the posterior bladder wall. At the end of this process, the
ureters normally terminate at orifices located at the superolateral corners of
the trigone.
If, however, a ureteric bud is in a
more cranial position on the mesonephric duct, the ureter is drawn farther than
usual into the bladder during mesonephric duct exstrophy. As a result, the
ureteric orifice may appear in a more inferior and medial position, such as at
the bladder neck or urethra. If the ureteric bud is even more cranial on the
mesonephric duct, the ureter may not be drawn into the bladder at all, instead
remaining attached to the mesonephric duct. In males, the ureter may
consequently terminate in any of the mesonephric duct derivatives, which
include the seminal glands (vesicles), vas deferens, or epididymis. In females,
the ureter may end in vestigial mesonephric duct derivatives, such as the
epoöphoron and paroöphoron, and then become incorporated into adjacent
structures, such as the vagina, uterus, and uterine (fallopian) tubes. Ectopic
ureters are usually seen as part of a duplicated collecting system (see Plate
2-23), in which the affected side has one ureter with a normally positioned
orifice and another with an ectopic orifice. This association is logical
because complete ureteral duplication occurs when a single mesonephric duct
sprouts two ureteric buds, one of which must be in an abnormal position.
Ectopic ureters are also frequently associated with renal hypoplasia or
dysplasia because the abnormally positioned ureteric bud fails to induce normal
differentiation of the metanephric mesenchyme.
Presentation And Diagnosis
Ectopic ureters may or may not be
symptomatic. In males, the common sites of ectopia are all located proximal to
the external urethral sphincter, and thus incontinence is not seen. An
insertion into the prostatic urethra, however, may lead to urinary frequency
and sensations of urgency. Reflux into the ectopic ureteric orifice is often
present, and thus upper tract infection may occur. Likewise, an insertion into
the epididymis may cause epididymitis. In females, many of the common sites of
ectopia are located distal to the external urethral sphincter. Thus many
females have constant urine drib- bling despite otherwise normal voiding
patterns. In both sexes, an ectopic ureter can become obstructed, causing flank
pain or even a palpable mass.
An ectopic ureter may initially be
seen on ultrasound, either with or without associated renal (hypo)dysplasia. If
there is ureteral obstruction, hydroureteronephrosis will be seen. If an
ectopic ureter is suspected, high-resolution axial imaging or a VCUG can often
provide additional information. With females, careful cystoscopy,
vaginoscopy, and inspection of the urethrovaginal septum may even provide
direct visualization of the ectopic ureteric orifice. In males, careful
cystoscopy and examination under anesthesia may also be diagnostic.
Once an ectopic ureter has been
identified, a renal scan should be performed to assess the function of the
associated renal parenchyma.
Treatment
Because ectopic ureters are often
associated with dysplastic kidneys, the treatment usually consists of
nephroureterectomy or, in the case of a duplicated collecting system,
heminephrectomy. If, in contrast, the renal parenchyma associated with the
ectopic ureter appears to be functional, or if there are bilateral ectopic
ureters, ureteropyelostomy or ureteral reimplantation can be performed instead.
