Excerpt from Prune Belly Syndrome

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In 1839, Frölich first described prune belly syndrome (PBS), and Osler gave the condition its name. Prune belly syndrome is also called Eagle-Barrett syndrome and triad syndrome.

Treatment of prune belly syndrome poses a significant problem to pediatric urologists. Some authors call for conservative management of the urinary tract in boys with prune belly syndrome, while others advocate an aggressive approach, operating on patients aged 10 days.

No definitive timing for therapy has been substantiated. Pediatric urologists have observed that boys with prune belly syndrome can present with a spectrum of abnormalities. At one end of the spectrum, the condition may cause severe urogenital and pulmonary problems incompatible with life (resulting in stillbirth); at the other end of the spectrum, the condition may cause few, if any, urological abnormalities that require no treatment other than orchidopexy to correct the undescended testis. The decision to aggressively treat the urinary tract of these children should be based on the clinical presentation and not solely on radiographic appearance.

Problem

Children with prune belly syndrome can present with myriad renal, ureteral, and urethral abnormalities. Obstruction and/or upper urinary tract dilatation is not unusual in these children. The site of obstruction can vary from as high as the pelviureteral junction to as low as the prostatic membranous urethra.

A lack of abdominal muscles leads to a poor cough mechanism, which, in turn, leads to increased pulmonary secretions. Weak abdominal muscles lead to constipation because of an inability to perform the Valsalva maneuver, which helps push the stool out of the rectum during defecation.

The mortality rate associated with prune belly syndrome is 20%.

Frequency

Prune belly syndrome affects 1 per 30,000-40,000 live births. Approximately 3-4% of all prune belly syndrome cases occur in females. Twinning is associated with prune belly syndrome; 4% of all cases are products of twin pregnancies.

Etiology

Prune belly syndrome is associated with trisomy 18 and 21. Patients with prune belly syndrome also have an increased incidence of tetralogy of Fallot (TF) and ventriculoseptal defects.

Pathophysiology

In 1903, Strumme proposed that the syndrome may be caused by in utero bladder obstruction, stating that dilatation of the urinary tract in utero leads to secondary-pressure atrophy of the abdominal wall and the subsequent clinical findings. More recent theories focus on a functional obstruction due to prostatic hypoplasia that leads to a conformational change in the prostatic urethra during voiding, thereby causing obstruction. The most recent theories suggest a transient obstruction at the junction of the glanular and penile urethra. This would explain the high incidence of megalourethra observed in cases of prune belly syndrome.

Considering the recent knowledge regarding high-pressure voiding and reflux, the theories involving urethral abnormalities can also explain the upper tract deformities that this syndrome can cause. High-pressure voiding has been discovered to lead to reflux in patients without prune belly syndrome. The obstructive process that occurs may impart a similar effect that mimics the dyssynergic voiding in persons with reflux. This high-pressure voiding thereby leads to changes in the location of the ureter, as well as the deleterious effects of the water-hammer effect on the renal tissue. Therefore, this abnormal high-pressure voiding process could explain reflux that is encountered along with renal dysplasia. The overdistended bladder could result in the abnormal development of the abdominal wall musculature and prevent the descent of the testis.

The histopathology of the abdominal wall muscles demonstrates a pattern of developmental arrest rather than one of atrophy. This also is suggested by a lack of any aponeurotic layers.

Fetal ascites, which may be transient because the urine is reabsorbed before birth, may explain the abdominal wall defects.

The prevailing theory is mesodermal arrest, which would explain the involvement of the genitourinary tract, the testis, and the abdominal wall. A noxious insult would have to occur between the 6th and 10th weeks of gestation. Some place the insult at 3 weeks of embryogenesis, which may explain the prostatic hypoplasia and poor glandular development. The mesodermal arrest theory is supported by the histologic findings in the abdominal wall, the urinary tract, and the male genital system. The abundance of fibrous tissue, collagen, and connective tissue with sparsely placed smooth muscle throughout the urinary tract indicates more of a mesodermal differentiation problem than one of obstruction.

The yolk-sac theory is based on the overdevelopment of the allantoic diverticulum that grows out from the yolk sac contiguous with the body stalk. If it becomes enlarged, it is incorporated into the urinary tract as a redundant enlarged urachus, bladder, and prostatic urethra. Unfortunately, this theory does not explain the abnormalities in the development of the upper urinary tract or male genital tract.

Clinical

See Relevant Anatomy.

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