ANOMALIES OF
THE URACHUS
As described on page
32, the urorectal septum partitions the cloaca into the primitive urogenital
sinus and the rectum. The urogenital sinus, which gives rise to the bladder, is
initially continuous with the allantois, a tube that extends into the
connecting stalk (see Plate 2-4 for an illustration). As the bladder matures
and descends into the pelvis, however, the allantois narrows to form a thick,
epithelial-lined tube known as the urachus. Normally the urachus regresses into
a fibrous cord, known as the median umbilical ligament. For uncertain reasons,
however, this normal regression process sometimes fails, resulting in a
persistent urachus that is either partially or completely patent. Because many
urachal anomalies are undiagnosed, their overall incidence is unknown.
Presentation And Diagnosis
An entirely patent urachus, which permits drainage of urine from the
bladder to the umbilicus, accounts for about half of urachal anomalies. It
typically presents during the neonatal period as dribbling of fluid from the
umbilicus. The fluid leakage may increase in response to bladder contraction
during either purposeful voiding or other increases in intraabdominal pressure,
such as during crying or straining. Umbilical edema and delayed healing of the
umbilical stump may also be noted. The diagnosis can be confirmed with either
sonographic evaluation of the bladder or with more invasive studies, such as a
retrograde fistulogram or voiding cystourethrogram (VCUG).
A patent area at the distal end of the urachus, which communicates with
the umbilicus, is known as a superior urachal sinus (or umbilical-urachal
sinus) and accounts for 15% of urachal anomalies. Like a patent urachus, a
superior sinus causes umbilical discharge during the neonatal period, although
the fluid is not as copious. The diagnosis is best established by performing
retrograde sinography.
A patent area in the middle of the urachus, which communicates with
neither the umbilicus nor bladder, is known as a urachal cyst and accounts for
about 30% of urachal anomalies. A urachal cyst is often not discovered until
childhood or adulthood. It may be noted as an incidental finding during
laparotomy; as a palpable midline mass; or as a site of infection, usually with
Staphylococcus aureus, with associated pain and erythema. Either
ultrasound or computed tomography can be used to establish the diagnosis.
Finally, a patency in the proximal end of the urachus, which communicates
with the apex of the bladder, is known as an inferior sinus (or vesicourachal
diverticulum) and accounts for 5% of urachal anomalies. It usually does not
cause symptoms because it is has a large opening into the bladder lumen and
does not communicate with other structures. In rare instances, however, it may act as a site of calculus
formation or lower urinary tract
infection. A VCUG, usually performed for some other indication, can establish
the diagnosis.
Treatment
A patent urachus or superior sinus should be excised using either an open
or laparoscopic technique. It is essential
to remove all abnormal urachal tissue because there is a small risk of later malignant transformation. Thus, in
addition to the urachus, a cuff of surrounding bladder tissue should be removed
as well.
An asymptomatic urachal cyst or inferior sinus can be managed with
careful observation since spontaneous resolution is possible. If resolution
does not occur, however, or if symptoms merge, all urachal tissue should be carefully excised.
