CHAPTER 8 Prune-Belly Syndrome
What are alternate, perhaps less stigmatizing, names for prune-belly syndrome?
Prune-belly vividly describes the clinical appearance of most patients with the syndrome. However, many clinicians consider the negative connotations to be stigmatizing and socially undesirable. Thus, several alternatives have been proposed. Eagle–Barrett syndrome recognizes one of the original descriptions of a series of 9 patients in 1950. Abdominal wall deficiency syndrome is a descriptive nomenclature. Triad syndrome emphasizes the 3 components of the classic syndrome. Nonetheless, prune-belly syndrome remains the common terminology, in part because of its intensely descriptive nature.
What are 3 classic features that characterize prune-belly syndrome?
Triad syndrome refers to the following 3 specific features of prune-belly syndrome:
1. Urinary tract dilation, specifically megaureter.
2. Abdominal wall deficiency.
3. Cryptorchidism.
The defective abdominal musculature gives the typical appearance of a wrinkled prune, with laxity of the anterior abdominal wall. The testes are both nonpalpable. The urinary tract dilation includes tortuous, dilated ureters, as well as varying degrees of an enlarged smooth-walled bladder and dilated prostatic urethra.
What is the approximate incidence of prune-belly syndrome?
The true incidence is not well known. The estimated incidence is similar to that of bladder exstrophy. The reported range is 1 per 29,000 to 40,000 live births. With increasing prenatal diagnosis and termination, the incidence has been decreasing. The classic triad syndrome only occurs in males. However, variations that include 2 of the 3 features can occur in males and females. The incidence is uncertain for patients with incomplete prune-belly syndrome, but probably is one-fourth as common as the classic syndrome. Furthermore, approximately 15% of patients with incomplete prune-belly syndrome were females. More common in twins, African Americans, and kids born to younger mothers.
What is the incidence of prune-belly syndrome in females?
Of all prune-belly syndrome cases, 3% to 5% occur in females.
What is the most common genetic karyotype in patients with prune-belly syndrome?
Normal. However, several genetic defects are associated with prune-belly syndrome. These include Turner syndrome, Monosomy 16, Patau syndrome (trisomy 13), Edward syndrome (trisomy 18), and Beckwith–Wiedemann syndrome.
To what does pseudo-prune-belly syndrome refer?
Incomplete prune-belly syndrome refers to patients with 2 of the 3 classic findings of the triad. For females, this would include the dilation of the urinary tract and lax abdominal wall musculature, but not the undescended testes. Pseudo-prune-belly syndrome refers to those males with ureteral dilation and undescended testes, but normal abdominal wall. Fifty percent will go on to renal failure often due to delay in diagnosis.
What percent of patients will have atypical presentation of prune-belly syndrome?
An incomplete form of prune-belly syndrome is present in as many as 25% of patients. Most will have the typical urinary tract finding of dilated ureters, but will have either normal abdominal wall musculature (pseudo-prune-belly syndrome) or descended testes. Females with incomplete prune-belly syndrome are even less common, affecting less than 5% of patients with the syndrome. In females, the urinary tract dilation may be less severe.
How does prune-belly syndrome present in females?
Prune-belly syndrome is uncommon in females and makes up just 5% of all prune belly syndrome patients. Females don’t have gonadal anomalies. They have abdominal wall and genitourinary tract anomalies only. Forty percent have anorectal anomalies and bladder outlet obstruction is common. Forty percent of females with prune-belly syndrome die during the neonatal period.
What are some proposed embryologic etiologies of prune-belly syndrome?
There are several theories explaining the embryogenesis of prune-belly syndrome. Each theory has both supporting experimental and empiric evidence, but none been proven. These theories are not mutually exclusive.
Urinary tract obstruction may result from a transient urethral membrane at a critical phase of development. Abdominal wall laxity then results from outward compression from the dilated urinary tract. The migration of the testicles is blocked by the enlarged bladder. Primary prostatic maldevelopment with hypoplasia of the prostatic urethra is another possible cause of urinary tract obstruction. A final postulated cause is felt to be due to transient obstruction at the glanular and penile urethral junction. In any case, fetal urinary ascites may or may not occur.
Primary mesodermal maldevelopment may also explain prune-belly syndrome. Failure of myoblast precursors to differentiate and/or migrate appropriately may explain the abnormal development of the abdominal wall. The laxity of the abdominal wall may then be the primary event. The decreased intra-abdominal pressures then result in urinary tract dilation and undescended testicles. However, if the developmental defect occurs early enough (3rd week of gestation), then all of the abnormalities may be explained by a common event in the mesenchymal tissues.
Persistence of the yolk sac has been implicated in the abdominal wall abnormalities resulting in redundant tissues. The allantoic diverticulum becomes overdeveloped and becomes incorporated into the urinary tract as redundant tissues.
Which is the prevailing theory?
Mesodermal arrest. This is thought to occur between the 6th and the 10th gestational week although it could occur as early as 3 weeks gestation.
Histopathology of the abdominal wall muscles is suggestive of what type of etiology: developmental arrest or muscular atrophy?
Developmental arrest. The lack of aponeurotic layers supports this etiology.
What are the 3 categories of prune-belly syndrome?
Category I has marked oligohydramnios secondary to dysplasia or severe bladder outlet obstruction, pulmonary hypoplasia, and Potter features. Prognosis is very poor in this group as most are either stillborn or die within the first few days of life. Little intervention is warranted in this group. A common intervention for this category is catheter drainage. This consists of 20% of the cases.
Category II shows minimal or unilateral renal dysplasia, full triad features without pulmonary hypoplasia. The course tends to be variable from stabilized renal function to progressive azotemia. This would include patients with urethral atresia and a patent urachus. The goal of treatment in this group is to stabilize renal function. The treatment in this category has the most controversies. This consists of 40% of the cases.
Category III consists of patients with mild or incomplete forms of prune-belly syndrome. There is no renal dysplasia or pulmonary insufficiency seen. There is stable renal function. Invasive treatment is necessary in those patients with recurrent infections. This consists of the remaining 40% of the cases.
Fetal ascites may be transient in prune-belly cases. Why?
It is reabsorbed, usually before birth.
What is the role of prenatal diagnosis with fetal ultrasound in prune-belly syndrome?
In general, prenatal diagnosis of prune-belly syndrome has not been reliable. There are high false-positive and false-negative rates of prenatal diagnosis. The typical intrauterine appearance of prune-belly syndrome is bilateral hydronephrosis with an enlarged noncycling bladder. Earlier fetal ascites and oligohydramnios may also be suggestive of prune-belly syndrome. However, the differential diagnosis of these findings includes posterior urethral valves, vesicoureteral reflux, bilateral ureteropelvic junction obstruction, neurogenic bladder, and megacystitis/megalourethra syndromes.
When are most cases of prune-belly syndrome diagnosed?
During the 2nd trimester.
What are the antenatal findings of prune-belly syndrome?
Bilateral hydronephrosis and hydroureter, distended thin-walled bladder, and oligohydramnios. Oligohydramnios implies renal dysfunction, which leads to pulmonary hypoplasia.
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