ABSTRACT

Prune belly syndrome is characterized by a triad of abnormalities, including an absence or deficiency of abdominal wall musculature, cryptorchism and anomalies of the urinary tract. The characteristic deficiency of the abdominal wall musculature was first described by Frohlich in 1839.1 Parker first reported the association of the genitourinary anomalies with the deficient abdominal musculature.2 The term ‘prune belly syndrome’ was coined for this complex by Osler in 1901.3 Eagle and Barrett, in 1950, further defined the triad of absent abdominal wall musculature, undescended testes and urinary tract abnormalities.4 The incidence of prune belly syndrome is estimated to be one in 29 000 to one in 50 000 live births.5-13 Apart from the claim by Adeyokunnu and Familusi of an increased incidence of prune belly syndrome in Nigeria, it does not occur with increased incidence in specific racial groups or geographic locations.10 This syndrome occurs almost exclusively in boys.13 It is very rare in females;13 only 5% of cases described in the world literature have been reported to occur in females.4-6,14

The pathogenesis of prune belly syndrome remains controversial and many theories have been proposed to explain it.3,4 One theory proposes that prenatal obstruction or dysfunction of the urinary tract causes urinary tract dilatation, fetal abdominal distension and subsequent muscle wall hypoplasia and cryptorchism in males.5,6,15-17 An embryological theory proposes that failure of primary mesodermal differentiation leads to defective muscularization of both the abdominal wall and the urinary tract.6,15-17 Although both theories explain some elements of the syndrome, they fail to explain others. Reinberg et al. recently suggested that the two theories should be regarded as complementary mech-

anisms, both operating in any given case.18 They theorized that teratogenic agents produce abnormal development of derivatives of the lateral plate mesoderm and abnormal epithelial-mesenchymal interactions, resulting in abnormal organ development and mechanical or functional obstruction of the urinary tract. Recently Stephens and Gupta proposed a theory of abnormal development of the intermediate mesoderm as a key factor in the pathogenesis of prune belly syndrome.5,19

This theory has two features: the first is that the terminal part of the wolffian duct is incorporated into both the prostatic and membranous urethra, and the second is that during incorporation, the ducts including their ureteric buds overexpand. Abnormal ectasia of the terminal wolffian duct occurring between 6 and 10 weeks’ gestation may produce saccular dilatation of the prostatic urethra, prostatic hypoplasia, and the valve-like obstruction in the membranous urethra. The ectasia could explain the attenuated bladder trigone and laterally placed wide ureteric orifices. Involvement of ureteric buds may also produce irregular megaureters. Renal dysplasia can be explained as a result of primary dysplasia of the methanephros or secondary to ureteric ectopia.