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Kidiu'v lntcrnaiio,wl Vol. 20 (/98/) pp 695—699

Etiology and pathogenesis of the prune belly syndrome

EBERHARD STRAUB and JURGEN SPRANGER

(/,iI/ren's Hospital, Uni'ersitv of Molar, Ma/ar, Germany

The congenital triad of abdominal muscle deficiency, severeurethra was somewhat less distinct in the 2 girls. Appropriate urinary tract abnormality, and forms a rare hutradiographic investigations and cystoscopic examination re- well-defined clinical condition popularly known as the "prunevealed some type of urethral stenosis in only 4 patients (exclu- belly syndrome" (PBS) 11—101. The term "prune belly" is sively males). Six boys displayed visible (partial) agenesis of the descriptive of the characteristic wizened, dried-plum appear-abdominal wall musculature, corresponding to the "classical" ance in the newborn and young infant (Fig. I). The peculiar and,PBS. In 7 children, including the 2 girls, hypoplasia and/or in "classical" cases, pathognomonic aspect of the thin, trans-dysplasia of the abdominal musculature was confirmed by parent, redundant abdominal skin, which is loose rather thanmuscle biopsies, demonstrating a reduced number of partially stretched, nestling to the wobbly intestines at birth, becomesbroadened muscle fibres with loss of' coherence of the Z hands. less marked with advancing age. With age, the wrinkles flattenclumping of glycogen granules, and mitochondrial abnormali- out as the subcutaneous fat and intraabdominal content in-ties on electron microscopic studies, described in the literature crease, expanding further the flaring and floppy flanks and theas the "embryonal type" [5, II, 20, 21]. Bilateral cryptorchi- paunch. dism was recognized in 8 of the 12 boys. Of particular interest is In addition to the therapeutic challenge presented by thepatient 7, a 3-year-old boy with a classical prune belly and PBS, its etiology and pathogenesis have been controversial. bilateral cryptorchidism but with a normal urinary tract (Figs. 4 Earlier studies suggested a mesenchymal developmental arrestand 5). during the 6th to 7th week of gestation leading to coordinated defects of dependent structures [II, 121. Discussion Recently, an old hypothesis has been resurrected and extend- In the past, the question of whether the uropathy in the PBS ed 113—151. It explains the morphologic characteristics of theis of an obstructive nature has been the subject of vehement PBS as sequelae of' an intrauterine distension of the ,debate among urologists [9—lI, 16—18, 22—34]. The issue, how- usually by enlargement of' the bladder due to an obstruction ofever, was considered settled 19, 10, 24—27, 29—331 until the the proximal urethra 116—191. Operative removal of the ob-surprising renaissance in the pediatric literature of the hypothe- structing tissue such as an urethral valve would under thesesis that both the muscular abdominal wall defect and the circumstances be a logical measure in the affected newborn orintraabdominal retention of the testes were produced by urinary infant. tract distension [13--l5, 19]. The modern concept is based on Our personal experience with 14 patients with PBS and agrowing experience with technically improved endoscopes, critical analysis of the literature do not support the hypothesiswhich have disclosed clearly that the abrupt transition from the of a secondary pathogenetic sequence arising from a primaryextremely wide prostatic to the distal portion of the urethra is obstructive uropathy. PBS and the "urethral obstruction mal-caused not by a real valve or other cause of narrowing, hut formation complex" 114] are different conditions, which can herather by agenesis or hypoplasia of the prostate 19. 10. 2 1—27. separated by clinical, radiographic, endoscopic, and histologic29, 31, 33, 34]. The latter phenomenon is, in fact, confined evaluation. This distinction determines the choice of the mostalmost entirely to the PBS and could hardly be related to any effective form of therapy. infravesical obstruction because, despite voluminous residual urine, the intravesical fluid pressure is abnormally low in PBS Patients [30, 311. In addition, the phenomenon does not occur in cases of The clinical features of our patients, 12 males and 2 females;,isolated urethral valve. Close analysis of radiographs ol' this are summarized in Tables I and 2. The typically ectatic,region reveals unequivocal differences from pictures seen in extremely elongated, and tortuous ureters were present in 13"mechanical" urethral obstruction [9, 10, 22—27, 33, 34]. The patients. All of these patients had hypoplastic or dysplasticcaliber of the urethra at the level of the verumontanum usually kidneys and an enlarged bladder with considerable amounts cfis normal; also saccular diverticula and/or absence of a corpus residual urine. In the 6 patients with dilatation of the collecting system, the "hydronephrosis" was less pronounced than would be expected in view of the massiveness of the megaureters (Fig. 2). The boys in this group showed an extraordinary bulge in the Received forpublication April l. 1981 proximal urethra, associated with an abnormally small or 0085-2538/81/0020-0695 $01 .00 absent prostate (Fig. 3). The increased width of the proximal ©1981by the International Society of Nephrology 695 696 Straub and Spranger I

Fig.2. Intravenous urogram in a patient with the prune belly syndro,ne, demonstrating the characteristic elongation and tortuosity of the ureters without hydronephrosis.'

Fig. 1. Prune belly aspect still recognizable at the age qf /0 months

Fig. 4. Abdominal aspect of patient no. 7 at 3 years of age. The Fig. 3. Urethrogram in a patient with the prune belly syndrome. There characteristic wrinkles that contribute to the wizened, dried plum is an extreme ectasia of the proximal urethra (agenesis of the prostate) appearance, present during the first months of life have flattened out. but no real obstruction. Note the bilateral cryptorchidism and agenesis of the inguinal canal. Prune he/frsvndrwne 697

Table1. Characteristicsof patients with prunebelly snydrome (PBS) or obstructive uropathy PBS Obstructive uropathy Partial agenesis or hypoplasia of abdom. wall musculature + Cryptorchidism + Abnormalities of the inguinal canal + Agenesis or hypoplasia of the prostate -F — Extreme tortuosity of the massive megaureters + Dysplastic (or almost normal) kidneys -1- — Reduced ureteral fluid pressure -F- Reduced intravesical micturation pressure (Gross) hydronephosis — + Increased ureteral fluid pressure — + Increased intravesical micturation pressure — +

Table 2. Clinical features of our patients

Patients -- I 2 3 4 6 7 8 9 10 II 12 13 14

Age, rear,s 20 10 6 4 4 Vt- 3 8 6 4 4 I 5 /I2+ Sex M M M M M M M M M M M M F F — Characteristic PBS uropathy (ectasia & + + + + + + + + -F- + + + + extreme elongation/tortuosity of ureters) Renal dysplasia and/or hypoplasia + + + + - +. + + + + + + + Dilatation of the collecting system — — + + .-. + — + Vesicoureteral/renal reflux (uni or bilat.) — + + — + Communicating urachal cyst + + — — "Megacystis" (residual urine) + + -1- -- + + + + + + + + Moderate trabeculation of the bladder + — + * + Extreme and pathognom. (!) dilatation of the + + + + + — + + + + + prox. urethra )absence/hypopl. of prostate) Marked dilatation of the prox. urethra — + + Normal urethra — + — Urethral stenosis (valve?) + — + — — + + — Normal urinary tract — -- — + — — Chron. recurr. + + + + + + — + + + + + + Irreversible uremic syndrome — + - + — + — + Mild or (partly) reversed renal insuffic. + + — — + — — + — improvement of function by therapy Partial abdominal muscle agenesis + -r + + + + + ("classical" dried plum appearance) Abdominal muscle drsp/usiu/hvpop/usia — + + + + + + + (verification h biopsy: "incomplete" PBS) Cryptorchidism (bilateral) + + - + + + + -- — + + —

spongiosum (but no meatal stenosis) are frequently observed obstructive uropathy. the dome of the bladder is quite often distal to the "false," counterfeit obstruction 110, 24—28, 31, 341. capped with a urachal process or diverticulum. and a patent, Real stenotic alterations or valves of the posterior urethra are eventually huge, urachal cyst may be detected in PBS. the exception in PBS [10, 191; they were diagnosed in only 4 of Numerous other findings in the PBS are not explained by the our patients. Thus, PBS can occur in association with clear-cut assumption of a primary obstructive lesion of the urinary tract. urethral obstruction, but this combination is not a causal one. The muscle deficiency in PBS only rarely affects the entire Hence, most cases of congenital urethral obstruction will have abdominal wall, and it may be unilateral or assymmetric [9. 10. abdominal swelling but not a prune belly. Patients with urethral 34, 35]. In PBS with agenesis of the abdominal musculature atresia are stillborn or die shortly after birth and may present there is no histologic sign of an aponeurotic layer that might with various symptoms of the Potter (renal agenesis) syndrome represent atrophied muscles [9] as one would expect if the [19, 341. defect were due to degeneration following abdominal disten- The reduced intravesical fluid pressure in PBS [II. 23, 31Jsion. The type of abdominal wall defect usually present in PBS differs distinctly from the increased values measured in obstruc- is an infrequent feature in proven congenital obstructive uro- tive uropathy. The bladder wall shows no muscular hypertro- pathy. Conversely, the characteristic abdominal muscle agenesis phy or trabeculation [9, 10, 24—28, 31, 341; its augmented or ("embryonal") hypoplasia in PBS may be manifest with thickness results from hyaline-rich deposits [II, 20, 281. Ac- normal urinary tracts, as in our patient 7 and in a few females in cording to all surveys, and in contrast to the situation inthe literature [9, 10, 34. 35].Onthe other hand, typical PBS 698 Straub andSpranger

(see Refs. 1, 8, 16, 17, 35, and our patient 3). Megacystis could not be responsible for either the agenesis or dysplasia and/or abnormal location of the inguinal canal [6, 9, 10, 32, 38] or for the typical position of the testes at the high posterior abdominal wall in PBS [9, 10, 34]. Finally, the clinical course of PBS differs in many ways, usually unfavorably, from that in obstructive uropathy. Several authors have reported excellent results in preserving and im- proving renal function in PBS by extensive surgical reconstruc- tion (tapering and reimplantation of the eventually refluxing ureters, urethrotomy, abdominal wall plication) [16—18, 29, 39— 421. But, the majority of urologists now have arrived at a far more tentative position or even a "hands-off philosophy" [10]. They advise utmost caution in attempting to alter the urody- namics and the course of events in PBS by operative manage- ment, including drainage measures by nephrostomy, cutaneous ureterostomy or cystostomy (except for the emergency situa- tion or the rare patient with real obstruction) [9, 10, 31, 32, 34, 38, 43, 44]. The almost consistently disappointing long-term outcome of more or less aggressive operative procedures proba- bly is due to the resistance to therapy of the primary atony with ineffective peristalsis of the ureters and bladder and ensuing persistent urinary stasis. Because intraluminal fluid pressure is not increased in PBS (for the same pathophysiologic reasons), the threat of pressure-induced renal tissue deterioration by itself does not constitute an indication for surgical intervention. Fig. 5. Intravenous urogram showing a normal urinary tract (patient Conservative treatment will maintain renal function even better no. 7). if bacterial infection is kept under control, because tonicity and peristalsis of the urinary tract structures have a tendency to improve spontaneously [10, 23, 29, 32, 38, 43—45]. uropathy may be associated with a normal abdominal wall [10, These practical aspects alone should lead to the abandonment 24, 25,351. of the concept of PBS as a multiple anomaly syndrome second- The morphology of upper urinary tract abnormalities in PBSary to lower urinary tract obstruction. The bulk of other differs decisively from the well-known form in obstructiveevidence precludes the idea of urethral obstruction as the cause uropathy. The kidneys are nearly normal or, much more oftenof the PBS [14] and favors the concept of it being a generalized there are histologic features of a primary dysplasia with depos-developmental abnormality [46, 47] in which the individual its of cartilage, tubular irregularities, cystic areas, and strikinglymanifestations of the PBS are independent results of a disturbed pronounced vascularization. In contrast, the "hydronephrotic"inductor/organizer cell-cell interaction during early embryogen- rarefaction of a kidney dilated by obstruction and high intralu-esis. The "developmental abnormality" is thought to represent minal pressure is not seen [10, II, 21, 23, 35, 36]. The calycesan area of segmenting mesoderm lateral to the notochord from are elongated, have a bizarre configuration, and are mostlywhich multiple structures including kidneys, genitourinary reduced in number [9, 10, 21, 25—30, 32, 341. Obstructivetract, and abdominal wall originate [48]. The cause and nature uropathy does not initiate the grotesque tortuosity of the uretersof the generalized disturbance are unknown. of PBS with grossly enlarged and relatively "normal" segments Summary. The hypothesis explaining the characteristics of alternating [10, 24—27, 34]. The smooth muscles in PBS arethe prune belly syndrome (congenital partial absense of the replaced to a great extent by fibrous tissue [II, 23], whereasabdominal wall musculature, severe urinary tract abnormali- congenitally obstructed ureters show muscular hyperplasia. ties, and cryptorchidism) as sequelae of a primary obstructive In this context, the paucity and dysplasia of the nerve plexusuropathy is supported neither by evidence from the literature and the irregularities of the Schwann cells [371 may havenor by our own observations. Critical analysis of the known pathogenetic significance in the atony of the ureters and thefacts favors the concept of a developmental field complex in ensuing insufficiency of urine transport in PBS. Even in cases ofwhich the various manifestations of the prune belly syndrome PBS with enormous ureteral (and vesical) distension, the intra-are produced by an early mesodermal defect. luminal fluid pressure is low rather than elevated as in obstruc- tive uropathy [10, II, 23, 30, 31]. Reprint requests to Prqf. ES t,auh, Children's Hospital. Stiidtisches Statements such as "testicular descent would be blocked by Krankenhaus Hoechst, Gotenstral3e 6—8, 6230 F,'ankfurt a rn. 80. Ge,'— distension of the bladder" [131 and "cryptorchidism .. . ap- many pears to be secondary to the massively dilated bladder obstruct- References ing descent of the testes" in PBS [14] are refuted by the fact that 1. 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