PBS is characterized by a low-pressure dilated urinary system from the urethra to the renal pelvis. A typical bladder in PBS patients will be massively enlarged and smooth-walled without trabeculations. Histologically, muscle fibers are replaced by collagen and fibrous tissues. This loss of muscle fibers causes the bladder to bulge in multiple directions, giving the appearance of a pseudodiverticulum at the bladder dome ( Fig. 59.2 ). A patent urachus is present in 25%–30% of PBS patients. The bladder neck is poorly defined, and the urethra is dilated, with mucosal folds giving the appearance of obstruction on imaging. ^{, ,} PBS patients typically demonstrate a normal compliance on urodynamic studies. However, a very large bladder capacity and a delay in the first sensation to void are often seen. ^, PBS bladders demonstrate poor detrusor contractions and variable emptying, with only 44% of PBS patients voiding spontaneously and 50% of patients having normal flow rates, voiding pressures, and low postvoid residuals. ^, Regardless of the voiding pattern, all PBS patients should be closely followed because bladder function may deteriorate throughout their life.

Appearance of a pseudodiverticulum at the bladder dome in a child with prune belly syndrome. The pseudodiverticulum develops because of the loss of muscle fibers in the bladder, which are replaced by collagen and fibrous tissue.

The trigone is wider and the bilateral ureteral orifices are displaced more lateral than usual, which likely contributes to the presence of vesicoureteral reflux (VUR) in 75%–80% of patients ( Fig. 59.3 ). ^{, , ,} The ureters are tortuous and severely dilated. ^, The degree of ureteral pathology can vary and has been shown to be segmental, with the distal ureter being the most affected ( Fig. 59.4 ). ^, Distally, the ureters have shown a greater decrease in muscle fibers and an increase in collagen and connective tissue fibers, which makes the proximal ureter more useful than the distal ureter for reconstruction. ^, This change in muscle fibers causes inefficient ureteral peristalsis and the development of upper tract urinary stasis and system dilation. ^{, , ,} Obstruction at the ureterovesical junction (UVJ) and ureteropelvic junction (UPJ) are not common but have been reported. As the child grows and the ureters elongate, spontaneous improvement may occur in the ureteral appearance and function. ^,

Voiding cystourethrogram in a patient with prune belly syndrome shows large, dilated distal ureters. The bladder is marked with an asterisk.

Marked dilation of the distal ureter ( asterisk ), which is often found in a child with prune belly syndrome.

Renal abnormalities range from completely normal to severely dysplastic kidneys. Dysplasia is present in 50% of PBS patients and in some cases, one kidney may be affected, with a normal contralateral kidney. The presence of hydronephrosis is also quite variable, and the degree of hydronephrosis does not correlate with the degree of dysplasia. ^, Hydronephrosis, when present, is typically nonobstructive. Progressive uropathy is known to occur, and nearly 20%–30% of PBS patients will progress to renal failure. The most accurate predictor of progression to end-stage renal disease (ESRD) is a nadir creatinine >0.7 mg/dL in the first 8 months of life. The degree of urinary system dilation is not a prognostic factor for renal function. Renal infection provides the greatest risk to renal function, and while early progression to ESRD may be attributed to severe renal dysplasia, later progression is attributed to renal damage from repeated infections and obstruction. ^{, , , ,} Many patients with PBS will ultimately require renal transplantation.

Several urethral anomalies have been described, including urethral obstruction and megalourethra. Although rare, obstruction of the urethra has been described in 20% of cases including urethral atresia, posterior urethral valves, and urethral stenosis. ^, Urethral atresia is usually fatal unless associated with a patent urachus, which allows drainage of urine. PBS is also associated with both types of megalourethra. ^, Scaphoid megalourethra, the most common and less severe form, is the deficiency of corpus spongiosum with intact bilateral corpora cavernosa ( Fig. 59.5 ). Fusiform megalourethra occurs when there is complete absence of corpus cavernosum and corpus spongiosum. ^{, ,} With fusiform megalourethra, when the patient voids, the entire penis will enlarge, while with scaphoid megalourethra, only the anterior urethra dilates with voiding. Megalourethra is more commonly seen in PBS than any other syndromes, with 50% of cases occurring in association with PBS. ^{, ,}

Scaphoid megalourethra.

As mentioned, children with PBS have hypoplasia of the prostate and resultant dilation of the posterior urethra ( Fig. 59.6 ). The normal prostatic smooth muscle and epithelium are replaced by connective tissue. The prostatic urethra tapers as it becomes membranous due to redundant folds of mucosa, which may give the impression of obstruction on imaging. ^, Adult men with PBS usually have infertility that is multifactorial in etiology. Cryptorchidism, prostate secretory disorders, and retrograde ejaculation are contributory.43 Ejaculatory failure may occur due to the lack of normal prostatic tissue and retrograde ejaculation can result from the incompetent bladder neck. ^{, ,} In addition, the vas deferens and the seminal vesicles are typically atretic, but dilation of these structures has also been described. Finally, there may be poor attachment between the testis and epididymis and between the efferent duct and the rete testis.

Posterior urethral dilation ( asterisk ) is often found in children with prune belly syndrome. This dilation is similar to that seen in boys with posterior urethral valves.

Abdominal-wall muscle deficiency is one of the most distinctive features in PBS. The abdomen has a wrinkled “prune like” appearance with bulging flanks ( Fig. 59.1 ). The degree of muscle deficiency varies, but typically the medial and inferior aspects of the abdomen are more severely involved. ^, In some cases, the musculature of the abdominal wall may be totally absent. As PBS children grow, the deposition of cutaneous abdominal adipose tissue increases reducing wrinkles, and a potbelly appearance ensues. ^, Due to the lack of abdominal support, they may develop lordosis. Gait usually is not affected, but walking may be delayed, and PBS infants tend to roll on their side in order to sit up. Due to poor lower chest-wall support, PBS patients also have a poor cough and are more prone to respiratory infections. ^,

Cardiopulmonary anomalies are present in 49%–60% of PBS patients. ^{, , ,} During the neonatal period, stabilization and management of cardiac and pulmonary anomalies may take priority over genitourinary conditions. A significant number of PBS patients have patent ductus arteriosus, atrial septal defect, ventricular septal defect, or tetralogy of Fallot. ^, Patients can also suffer from pulmonary hypoplasia due to oligohydramnios, caused by bladder outlet obstruction (BOO), and renal dysplasia. Nearly half of PBS patients may need mechanical ventilation during the neonatal period. If severe pulmonary hypoplasia is present, it can result in newborn demise. Other associated lung anomalies include pneumothorax or pneumomediastinum. Reactive airway disease is found in 22% of patients, and as mentioned, due to poor lower chest-wall support, PBS patients have poor cough effectiveness and are more prone to respiratory infections and atelectasis. ^, It is also very important to note that PBS patients are more prone to respiratory failure from acute respiratory illness or anesthesia. Older patients may also develop restrictive lung disease secondary to musculoskeletal abnormalities. ^,

Greater than 30% of PBS patients suffer from gastrointestinal conditions, with one study demonstrating that 63% of living PBS patients have gastrointestinal diagnoses. ^{, ,} The majority of anomalies are due to incomplete rotation of the midgut and the development of a wide mesentery, which may lead to increased bowel mobility in the capacious abdominal cavity predisposing patients to volvulus. In addition, intestinal atresia and stenosis have been reported. Intestinal atresia is more common than stenosis, with most occurring in the colon. Omphalocele, splenic torsion, gastroschisis, and anorectal malformations have also been described. ^{, ,} Constipation affects 58% of PBS patients and is a lifelong problem due to the inability to generate adequate intraabdominal pressure, which may lead to acquired megacolon. ^,

Musculoskeletal anomalies are present in 21%–65% of PBS children. ^{, ,} The etiology of such abnormalities is suspected to be in utero compression and the sequelae of oligohydramnios. The most common deformities are clubfoot and scoliosis, which are each seen in about a quarter of patients. Hip dysplasia, pectus excavatum/carinatum, and sacral agenesis have also been described.

There is a broad spectrum of disease severity, with some PBS patients not surviving the neonatal period, and others with minimal symptoms and near-normal life expectancy. Woodard described a classification system to aid in patient management in which PBS patients are sorted into three groups. ^{, , ,} These categories, with their characteristics, prognosis, and management, are described in Table 59.1 .

Among the classic triad of PBS is bilateral intraabdominal undescended testes. The most common location of the testes is above the iliac vessels and adjacent to the dilated ureters. Data regarding PBS testicular histology is varied, with some reports stating no difference in germ cell count, spermatogonia, and Leydig cells between undescended testes in PBS patients and undescended testes found in non-PBS patients. ^, Meanwhile, other studies have described diminished spermatogonia and Leydig cell hyperplasia in PBS fetal testes suggesting an intrinsic testicular abnormality. Regardless of histology, azoospermia with little or no germ cell maturation is usually found in adult PBS patients. Currently, no PBS patient has been documented as having fathered a child naturally. As stated previously, this infertility is thought to be multifactorial. However, now with early orchidopexy, sperm retrieval, and microinjection of spermatozoa, PBS patients have better prospects for fertility, and more recently, the birth of two normal male infants was documented from a PBS father after intracytoplasmic sperm injection. ^, Cryptorchidism is also a well-known risk factor for testicular cancer, most commonly seminoma. ^, For this reason, PBS children should undergo early orchiopexy and long-term surveillance to improve testicular cancer detection.