Excerpt from Prune Belly Syndrome

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Background

Prune belly syndrome typically occurs in boys with a thin or lax abdominal wall; such laxity is variable in severity. The prostatic urethra is long and dilated as a result of prostatic hypoplasia. Some patients have a utricle diverticulum from the urethra; a large, vertically oriented, thick-walled bladder; a urachal remnant from the dome of the bladder; and tortuous and dilated ureters. Varying amounts of hydronephrosis and varying degrees of renal dysplasia are seen. All have cryptorchidism.

The amniotic fluid volume may be normal or decreased in neonates with prune belly syndrome. The presence of oligohydramnios may account for some of the accompanying findings of the extremities.^{1, 2, 3}

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Pathophysiology

The etiology of prune belly syndrome is not fully understood. The thinness of the abdominal wall has been attributed to hydronephrosis. The distended urinary system is thought to interfere with the normal descent of the testes. However, some patients with severe hydronephrosis do not have the same disorder of the abdominal wall. Cryptorchidism usually is not seen in patients with distended bladders of other etiology.^{4, 5}

Frequency

United States

Prune belly syndrome is a rare anomaly seen in 1 in 35,000-50,000 live births. The genetic origins remain unclear.

Mortality/Morbidity

Controversy exists concerning the management of prune belly syndrome. Management may consist of aggressive surgical repair involving tapering of the ureters and reimplantation, or surgical intervention may not be employed. An ideal approach has not been established; this is not surprising, given the varying degrees of clinical severity. Morbidity relates to the urinary tract; poor ureteral peristalsis and weak forward propulsion of urine in the ureters result in stasis, infection, and stone formation. Renal failure results from underlying renal dysplasia and the aforementioned complications of urinary stasis.

In the 1970s, half of the patients with prune belly syndrome died in early infancy. The survival rate has improved markedly. The severe abdominal distention is associated with pulmonary hypoplasia that is related to the patient's large abdominal content and compromise of the thorax during fetal development.

Race

Prune belly syndrome occurs in individuals of all races.

Sex

Prune belly syndrome occurs almost exclusively in males; less than 3% of cases of prune belly syndrome involve female patients.

In both genders, prune belly syndrome involves the abdominal wall, bladder, ureters, and kidneys. No urethral anomalies are seen in females. Males often demonstrate abnormality of the posterior urethra, resulting from abnormality of the posterior lobe of the prostate. Males occasionally also have nondevelopment of the corpora of the phallus.

Age

The diagnosis of prune belly syndrome is made in utero using ultrasound (US). In the neonate, the diagnosis is made on the basis of characteristic clinical findings. The diagnosis should be suspected in the fetus when US imaging reveals a characteristic enlarged bladder, dilated ureters, and an abnormal abdominal wall. However, the same constellation of US findings can signal posterior urethral valves with severe hydroureteronephrosis; thus, as a cautionary measure, the diagnosis should not be declared with certainty for either condition.

Occasionally, prune belly syndrome is reported in adults presenting with hypertension secondary to renal disease.

Anatomy

Abdominal wall

The abdominal wall defect in prune belly syndrome varies from a complete absence of musculature and scanty subcutaneous tissue to an abdomen with an apparently normal appearance. The lower portion of the abdomen usually is involved, and the flanks bulge. The margins of the liver and spleen, as well as bowel loops, are visible. The chest appears small with flaring of the lower ribs. The wrinkled appearance of the dystrophic abdominal wall is responsible for the prunelike appearance of the abdomen.

Urethra

The urethra may be normal, or portions of the corpus spongiosum may be absent; such absence is associated with megalourethra of the anterior urethra. The posterior urethra is elongated and dilated. It has a funnel-shaped appearance that resembles a posterior urethral valve; however, the presence of a valve is unusual in prune belly syndrome.

A persistent prostatic utricle usually is present in the posterior urethra at the verumontanum. Underdevelopment of the posterior lobe of the prostate gland results in a diverticulum-like posterior projection of the posterior portion of the urethra. The appearance is that of a prostatic utricle.

Bladder and urachus

The bladder in prune belly syndrome is large, vertical in orientation, and often thick-walled. In some patients, a bulging conical dome of the bladder represents persistent urachus. The bladder usually is distended at the trigonal region. Vesicoureteral reflux often occurs. A large postvoid residual volume is also a frequent occurrence.

Ureters

The ureters are markedly tortuous and dilated, with the distal ureter more affected than the proximal ureter. The wall of the ureter is fibrous, with deletion of the muscular layer. Ureteral function may at times improve with tapering.

Kidneys

Dilatation of the renal pelves with clubbing of the renal calyces and a diminished number of calyces is characteristic. The kidneys are hypodysplastic, often with diffuse parenchymal cysts. The degree of renal dysplasia does not correlate with the involvement of the abdominal wall or of hydronephrosis. Progressive renal failure occurs with repeated infection.

Testes

All male patients with prune belly syndrome have cryptorchidism. The testes are present; they are usually small and are located intra-abdominally. Whether the condition of nondescent represents a primary defect in relation to the absence of abdominal wall musculature is unknown. Sperm usually are absent. Neoplasia has been reported to occur in the testes.

Associated abnormality

In the GI tract, anomalies include malrotation with mesenteric defect, imperforate anus, gastroschisis, Hirschsprung disease, and constipation.

Cardiac

Cardiac anomalies in prune belly syndrome include ventriculoseptal defect and atrial septal defect; such defects have been reported in 10% of patients.

Pulmonary

Pulmonary anomalies include hypoplasia resulting from the oligohydramnios, compression from the large abdomen, and Potter syndrome (pneumothorax, pneumomediastinum). Respiratory compromise secondary to abdominal muscular deficiency may be seen. Pneumonia and atelectasis also are observed occasionally.

Extremities

Skin dimples over the joints are seen in patients with prune belly syndrome. Lower-extremity deficiencies are also seen; such deficiencies include clubfoot and developmental dysplasia of the hip, which occurs as a result of fetal crowding by oligohydramnios.

Clinical Details

See Anatomy.

Preferred Examination

To confirm prune belly syndrome, radiography is used to evaluate the abdomen and chest initially. For urinary tract evaluation, renal US and voiding cystourethrography are performed. For fragile neonates and for infants with severe reflux and retention, these simple diagnostic studies may be much more threatening than they are for the normal baby. The use of prophylactic antibiotics and the need to act upon the study results should be weighed before proceeding indiscriminately.

Some diagnosticians assess renal function by performing a technetium-99m (^99mTc) dimethylsuccinic acid (DMSA) renal scan. DMSA is a cortical agent; DMSA renal scans provide information about both the appearance and function of the kidneys.

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