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Imaging Case Book

Prune belly syndrome


A 3520-g infant was born at term to a 21-year-old gravida 2, para 1 mother. The pregnancy had been complicated by a sonogram demonstrating a distended bladder, dilated ureters, right club foot and oligohydramnios. At birth, the amniotic fluid was meconium stained and the infant was initially in respiratory distress. The Apgars were 4 at 1 min, 3 at 5 min and 9 at 10 min. On physical examination in the nursery, the baby was noted to have bilateral cryptorchidism and bilateral clubbed feet. An abdominal radiograph (Figure 1), renal sonogram (Figure 2) and voiding cystourethrogram (Figure 3) were performed.

Figure 1

Supine frontal view of abdomen. The right flank is bulging with very little abdominal wall tissue covering the air-filled right flank bowel loops. The ribs have a transverse orientation, sometimes referred to as a ‘coat-hanger’ deformity.

Figure 2

(a) Longitudinal sonogram right kidney, (b) longitudinal sonogram left kidney and (c) longitudinal sonogram urinary bladder. There is cystic dysplasia of the right kidney, manifested by peripheral cysts (arrows) and increased parenchymal echogenicity. The left kidney is also highly echogenic, but without cysts, and is also dysplastic. The bladder is slightly thick-walled and of very large volume.

Figure 3

(a) Oblique radiograph bladder, (b) voiding urethral film. A urachal diverticulum (arrow) is seen at the dome of the urinary bladder. The urethra is tortuous with a dilated prostatic urethra (arrowhead).

Denouement and discussion

The abdominal wall, renal, bladder and urethral abnormalities in this infant are those of prune belly syndrome (PBS). PBS is characterized by a triad of findings (and is sometimes therefore called triad syndrome). These include the following: (a) deficient abdominal musculature, (b) urinary tract anomalies with megacystis and megaureters and (c) cryptorchidism.1 The disease occurs in approximately 1 in 50 000 live births and 95% of patients are male. Most cases are sporadic, although rarely familial cases have been described. The skin of the anterior abdominal wall is wrinkled, thin and lax, which accounts for the prune-like appearance and the name of the syndrome. The anterior abdominal wall muscles are absent in 30% of cases, replaced by dense collagenous tissue and hypoplastic with areas of absence in 70%.2 The genitourinary anomalies consist primarily of renal hypoplasia, dysplasia, ureteral dilatation, megacystis, dilated prostatic urethra and prostatic hypoplasia.1 Variable degrees of renal dysplasia occur ranging from severe dysplasia with cartilage metaplasia to mild cystic dysplasia. The ureters are usually dilated, ectatic and thick-walled. There may be focal areas of ureteral stenosis and gigantism. The ureterovesical junction is usually widely patent and vesicoureteral reflux occurs in 75% of patients.1 The urinary bladder is enlarged, often thickened, but non-trabeculated. Between 25 and 50% of patients have either a patent urachus or urachal diverticulum. The prostatic urethra is dilated with a small verumontanum, and urethral obstruction is an associated finding reported in 0–100% of patients. Cryptorchidism is present in 95% of patients. Obviously, the entire triad is not present in female patients. In reviews of female patients with PBS, all patients have had urethral atresia,2, 3 which has increased interest that urethral obstructions are the underlying etiology of PBS. Calcifications occur in the bladder dome and urachus in some patients with PBS, which are dystrophic, possibly related to bladder distention.4

Although, over the years, many theories have been suggested to explain PBS, including persistent abnormal bladder fixation at the umbilicus, aganglionosis and a genetic cause—x-linked or sex-modified autosomal-recessive condition1—these theories have not been confirmed by histological examination, fetal sonography or twin studies. Currently, the most frequently discussed etiologies of PBS include urethral obstruction, mesodermal defect and abnormalities of the allantois. The latter theory is not widely held but suggests that the allantois is abnormally large and abnormally incorporated into the abdominal wall. This theory may be supported, however, by the very slight increased frequency of omphalocele in PBS patients.5 The mesodermal defect theory implies that a noxious event to the mesoderm prevents normal development of the abdominal muscles and urinary tract muscles. The theory of urethral obstruction is now most widely held.1, 6 This theory suggests that urethral obstruction at a certain period of fetal life leads to distention of the urinary system, urinary ascites and abdominal distention with degeneration of the abdominal muscles.1 The dilated bladder presents normal testicular descent. It is most widely believed that bilateral fetal obstructive uropathy leads to PBS, especially owing to urethral obstruction at the junction of the anterior and posterior urethra,4 but which may have been relieved by the time of delivery. This relief of presumably high-pressure urinary tract obstruction in utero explains why low pressure, non-obstructed urinary tract systems are often found in newborns with PBS.1 Fetal sonographic examinations have provided additional evidence that patients with PBS had ascites and abdominal distention in utero.7

Associated abnormalities in PBS patients, in addition to abdominal wall and genitourinary findings, are present in many patients. Approximately 30% of patients have malrotation and malfixation of the intestines.8 Intestinal atresia and stenosis are also not uncommon. Atresias are more common than stenosis, and most of the atresias occur in the colon, which is in marked contrast to the usual case in patients without PBS, in whom small bowel atresias are 13 times more common than colonic atresias.7 Imperforate anus and persistent cloaca also occur more frequently in PBS patients. Occasionally, an intermediate condition is present in which the rectum ends blindly in the bladder wall but without communication, which if present would have created a cloaca. Splenic torsion is also increased in frequency.8, 9 Many of these findings can be attributed to the abdominal distention with a capacious abdominal cavity allowing malfixation and an increased likelihood of intrauterine volvulus.

Orthopedic findings in PBS patients include talipes equinovarus (club foot), vertical talus and congenital hip dislocation.10 Lower extremity hypoplasia or aplasia also occurs. This is found to be more frequent on the right than the left. Occasional cases are associated with limb gangrene, suggesting that the cause is compression of the iliac/femoral vessels by the large urinary bladder.11 Pulmonary manifestations of PBS are variable in severity. The most severe is pulmonary hypoplasia associated with oligohydramnios and Potter's facies. Also common is lobar atelectasis and pneumonia due to poor ventilation because of deficiency of abdominal musculature and thoracic wall deformity.12

Patients are usually separated into three grades based on severity of renal and pulmonary malformations, Grade 1, those with oligohydramnios-induced pulmonary hypoplasia and Potter's facies; Grade 2, moderate-to-marked neonatal and infantile urinary tract involvement without pulmonary hypoplasia or Potter's facies; and Grade 3, mild renal involvement.13 Patients with Potter's syndrome die in the neonatal period and no treatment is effective. Those with mild involvement often do not require surgical intervention if the system is low pressure but drains adequately. However, infections must be prevented, especially those due to Proteus mirabilis and other urea-splitting organisms, which can lead to hyperammonemic encephalopathy14 in PBS patients without liver dysfunction. Urinary diversion is now used fairly conservatively to improve or maintain renal function.15 Orchiopexy and ureteral reimplantation have the same indications in PBS patients as in other patients.


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Correspondence to T E Herman.

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Herman, T., Siegel, M. Prune belly syndrome. J Perinatol 29, 69–71 (2009).

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