Prune Belly Syndrome (PBS), also known as Eagle-Barrett syndrome, is a rare, complex congenital disorder that affects multiple body systems and is present at birth. This condition primarily impacts the abdominal wall, the urinary tract, and the testes in male infants, who account for approximately 95% of cases. PBS presents a wide spectrum of severity, with outcomes ranging from severe complications requiring intensive care to milder forms compatible with a near-normal lifespan. The condition is defined by recognizing the three distinct anatomical abnormalities that define its clinical presentation.
Defining the Prune Belly Triad
Prune Belly Syndrome is clinically characterized by a distinct set of three abnormalities, collectively referred to as the triad. The first and most visually apparent component is the partial or near-total absence of musculature in the abdominal wall. This muscular deficiency causes the skin of the abdomen to appear thin, wrinkled, and loose, especially immediately after birth, which is the source of the syndrome’s name.
The flaccid abdominal wall provides poor support for the internal organs. This lack of muscle tone also severely compromises the ability to generate intra-abdominal pressure, which is necessary for effective coughing and urination. The reduced muscular strength can lead to difficulties with movement, such as sitting up or turning over, as the child grows.
The second feature involves significant abnormalities of the urinary tract, impacting the bladder, ureters, and often the kidneys. The bladder is typically enlarged and fails to empty completely. This chronic urine retention leads to the dilation and tortuosity of the ureters, known as megaureters, as well as the backup of urine into the kidneys, or hydronephrosis.
The third defining characteristic, seen in affected males, is bilateral cryptorchidism, the failure of both testes to descend into the scrotum. The testes usually remain high within the abdomen, a consequence related to the developmental issues affecting the abdominal wall and the genitourinary system.
Underlying Causes and Risk Factors
The precise cause of Prune Belly Syndrome remains largely unknown, but current understanding centers on developmental theories occurring early in fetal life. The most accepted explanation is the early fetal obstruction hypothesis, which proposes that a severe blockage in the lower urinary tract, such as in the urethra, occurs between the sixth and tenth weeks of gestation. This obstruction causes a massive buildup of urine, leading to extreme distension of the bladder and the upper urinary tract.
The prolonged pressure from the enlarged bladder exerts mechanical stress that prevents the proper development of the abdominal wall musculature, causing it to thin and atrophy. This distension is also believed to interfere with the normal descent of the testes into the scrotum. Alternatively, the mesodermal arrest theory suggests an intrinsic defect in the lateral plate mesoderm, the embryonic tissue that gives rise to the muscles of the abdominal wall, the urinary tract, and the supporting structures for testicular descent.
Most cases occur sporadically, but a small number of instances reported in siblings suggest a potential genetic component. While no single gene mutation has been definitively identified as the sole cause for all cases, specific genetic abnormalities, such as mutations in the HNF1β gene, have been associated with PBS in a small percentage of patients. The condition is overwhelmingly more common in male infants.
Diagnosis and Prenatal Detection
Identification of Prune Belly Syndrome often begins before birth through routine prenatal ultrasound screening. Characteristic findings on a fetal ultrasound may include an abnormally large, distended bladder, a lack of definition of the abdominal wall muscles, and dilated ureters or kidneys (hydronephrosis). In severe cases, the inability of the fetal kidneys to produce sufficient urine can lead to oligohydramnios, or low amniotic fluid volume, which can be a poor prognostic indicator.
Following birth, the diagnosis is confirmed by a physical examination that reveals the wrinkled abdomen and the absence of palpable testes in the scrotum. Postnatal imaging is essential to determine the extent of urinary tract involvement and to assess the functional status of the kidneys. A Voiding Cystourethrogram (VCUG) is a frequently used test that involves filling the bladder with a dye and taking X-ray images as the child voids to identify abnormalities like vesicoureteral reflux (urine flowing backward) or urethral obstructions.
Renal ultrasounds and nuclear medicine scans are also performed to evaluate the degree of kidney damage, or renal dysplasia, and to monitor the kidney’s filtering function. The severity of the urinary tract malformations, specifically the degree of renal impairment, is the most significant factor in determining the overall prognosis and subsequent treatment plan.
Medical Management and Long-Term Outlook
Management of Prune Belly Syndrome is highly individualized and requires a coordinated, multidisciplinary approach involving pediatric urologists, nephrologists, and general pediatricians. The primary goal of treatment is to preserve kidney function, ensure adequate bladder emptying, and prevent recurrent urinary tract infections (UTIs). Many patients receive long-term prophylactic antibiotics to reduce the high risk of infection caused by incomplete bladder emptying and urine stasis in the dilated urinary tract.
Surgical intervention is often necessary and can be divided into three main areas: Orchiopexy, Urinary Tract Reconstruction, and Abdominoplasty.
Orchiopexy, the procedure to bring the undescended testes into the scrotum, is performed to allow for easier cancer surveillance and, potentially, to preserve fertility.
Urinary tract reconstruction may be undertaken to reduce the size of the enlarged bladder and to address the dilated, poorly draining ureters. This sometimes requires a temporary measure like a vesicostomy to divert urine.
The third surgical component is abdominoplasty, or abdominal wall reconstruction, which tightens the flaccid abdominal wall muscles. This procedure improves the cosmetic appearance and enhances the patient’s ability to void and cough effectively, reducing the risk of pulmonary complications.
The long-term outlook for individuals with PBS is highly variable and directly correlates with the severity of the initial renal function. While severe cases may lead to chronic kidney disease or failure requiring dialysis or kidney transplantation, many individuals with milder forms of the syndrome can achieve a near-normal life expectancy with consistent medical surveillance and timely intervention.