PRUNE BELLY SYNDROME
The prune belly syndrome (PBS, also known as Eagle-Barrett or triad
syndrome) is a rare, congenital disorder that occurs almost exclusively in
males. Its major features include deficient abdominal wall musculature,
bilateral cryptorchidism, and urinary tract anomalies that include renal
dysplasia, hydronephrosis, and dilation of the ureters and bladder.
PBS occurs in approximately 3.5 per
100,000 live male births. Blacks are at increased risk and Hispanics are at
decreased risk when compared with the overall population. There are rare
reports of females born with deficient abdominal wall musculature and urinary
tract anomalies, although their ovaries are generally normal.
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Appearance
of abdominal wall in prune belly syndrome
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Pathogenesis
The pathogenesis of PBS remains poorly
understood. One theory argues that early obstruction of the bladder outlet causes
dilation of the bladder, ureters, and then renal pelves. Such dilation is
posited to cause an increase in intraabdominal pressure that results in atrophy
of the abdominal wall musculature and inhibition of normal testicular descent.
This hypothesis, however, is challenged by the fact that many patients with PBS
do not have an anatomic outlet obstruction, and that many patients who do have
such obstructions (such as those with posterior urethral valves) do not have
PBS.
Another theory argues that the primary
defect lies in the intermediate and lateral plate mesoderm, which gives rise to
the urinary tract, genital tract, and abdominal wall musculature (see Plate
2-1). The causes and nature of the mesodermal defect, however, remain unknown.
Because 1 in 23 children with prune belly syndrome is the product of a twin
pregnancy, however, at least some cases could reflect an uneven distribution of
mesoderm between twinned embryos early in gestation.
The genetics of PBS also remain poorly
understood. Although most cases are sporadic, a small number of familial cases
have been reported and suggest a sex-linked autosomal recessive pattern of
inheritance. Most affected infants possess normal karyotypes, but some
associations have been noted with trisomies 13, 18, and 21.
Presentation And Diagnosis
PBS can often be detected using
prenatal ultrasound, which has been shown to establish the diagnosis as early
as 11 weeks into gestation. Suggestive findings include hydronephrosis, bladder
enlargement, and absence of the abdominal musculature. If there is severe renal
dysplasia or a bladder outlet obstruction, oligohydramnios and pulmonary
hypoplasia may also be seen.
If PBS is not diagnosed in the
antenatal period, it is generally readily apparent at birth. The most striking
feature of affected infants is the wrinkled, prunelike skin overlying their
inferior abdominal wall, which reflects attenuation or outright absence of the
normal abdominal musculature. The abdominal wall may be so thin that the
underlying organs, including peristaltic regions of the bowel, become visible.
As affected children grow older and spend more time standing upright, the
wrinkles become less prominent, and the abdomen assumes a “pot-bellied”
appearance. The lack of abdominal musculature makes it difficult for affected
patients to sit upright from a supine position. Some reports have also
suggested that it increases the risk of pneumonia by impairing the normal
coughing mechanism, and that it can cause constipation by preventing the
generation of increased intraabdominal pressure.
Although all patients have
hydronephrosis, the degree of renal dysplasia is variable and has important
prognostic implications. Those with the most severe renal dysplasia develop the
Potter sequence (Plate 2-8) and typically succumb to severe respiratory
distress shortly after birth. Those with moderate dysplasia often develop
end-stage renal disease (ESRD) during childhood. Finally, those with minimal or
no dysplasia often maintain normal or near-normal renal function. To assess for
renal abnormalities, an ultrasound should be performed in the neonatal period,
and serial measurements of the serum creatinine concentration should be
obtained (recognizing that early values reflect maternal, rather than neonatal,
renal function). If there is evidence of renal dysfunction, a renal scan can
provide more detailed functional information.
The ureters appear broad and tortuous,
especially as they approach the bladder, and peristalsis is weak and
ineffective. These anomalies reflect a relative lack of smooth muscle cells in
the ureteral walls, which instead
consist primarily of fibrous connective tissue. In addition, the ureteric
orifices are often at abnormally lateral positions, which predisposes them to
reflux.
The bladder appears enlarged, with a
vesicourachal diverticulum often present. The bladder wall appears smooth and
thick secondary to increased collagen depo- sition. The detrusor muscle is
hypoplastic, which may cause weak bladder contractions associated with large
postvoid residuals. The combination of urinary stasis in the bladder, which
increases the risk of bacterial infection, and vesicoureteral reflux, which
permits passage of infected urine into the renal pelves, may lead to recurrent
pyelonephritis and progressive worsening of renal function. Thus if there is
evidence of bladder dysfunction, a VCUG should be performed after sufficient
antibiotic prophylaxis has been provided.
The bladder neck and prostatic urethra
appear widened, with the latter resulting from prostatic hypoplasia. The
prostatic urethra tapers to the membranous urethra, resulting in an inverted
triangle appearance on VCUG. The anterior urethra is typically normal. A small
subset of patients may have urethral dilation (megalourethra) owing to absence
of either the corpora spongiosum alone or, in rare cases, both the corpora
spongiosum and cavernosum. An even smaller number of patients have complete
urethral atresia, resulting in oligohydramnios and Potter sequence.
The testes are generally located in
the abdomen, near or above the iliac vessels. They appear histologically
abnormal, with a reduced number of spermatogonia, and are at increased risk for
malignancy. The combination of testicular dysfunction and prostatic hypoplasia
renders patients infertile. In addition, retrograde ejaculation is common
because of the open bladder neck.
Other organ systems show a variable
degree of involvement. Cardiac anomalies, seen in 10% to 20% of patients,
include septal defects and patent ductus arteriosus. Pulmonary anomalies
include pulmonary hypoplasia, which occurs in those with Potter sequence, as
well as pneumothorax. Early assessment for cardiopulmonary anomalies, including
a chest radiograph, is thus an important component of the postnatal evaluation.
Finally, gastrointestinal complications range from constipation, which occurs
in most patients, to serious anomalies such as intestinal malrotation or
anorectal malformations.
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Appearance
of kidneys, ureters, and bladder in prune belly syndrome
Treatment
Because recurrent pyelonephritis is
common and can lead to renal scarring, lifelong antibiotic prophylaxis should
be started during the postnatal period. In addition, urine cultures and
measurements of the serum creatinine concentration should be obtained on a regular
basis.
If bacterial infections continue to
occur, or if renal function appears to be deteriorating, the abnormal
collecting system may be reconstructed. The ureters are tapered and reimplanted
to reduce reflux. In addition, a reduction cystoplasty, which consists of
excision of the vesicourachal diverticulum or other redundant areas of mucosa,
may be performed to reduce the volume of retained urine. Although the majority
of patients empty their bladders adequately, a subset require clean intermittent
catheterization.
Abdominal wall reconstruction can
mitigate the psychological effects of PBS, and it may also improve constipation
and reduce the risk of pneumonia. The most popular technique, known as the
Monfort procedure, consists of an elliptical incision to remove redundant skin,
a second incision around the umbilicus so that it can remain in position, and
two vertical incisions through the abdominal fascia to overlap redundant
segments and increase the strength of the abdominal wall. Finally, early orchidopexy
is recommended in all patients because it often allows them to achieve normal
production of sex hormones at puberty. In addition, it greatly facilitates a
regular examination for testicular malignancies.
The prognosis of patients with PBS who
survive the postnatal period depends primarily on the severity and progression
of renal dysfunction. Unfortunately, even those who survive infancy with mild
renal impairment may progress to renal failure due to recurrent pyelonephritis,
particularly in patients who incompletely empty their bladders. Renal
transplantation has been shown to be a feasible option for these patients.
