Prune Belly Syndrome

Basics

Description

  • Rare congenital disorder characterized by the triad of
    • Deficiency of abdominal musculature
    • Bilateral cryptorchidism
    • Dilated, anomalous development of the bladder and upper urinary tract
  • Presents with a broad spectrum of severity, from mild hydroureter with an enlarged bladder and normal renal function to severe renal dysplasia and pulmonary hypoplasia
  • Also known as Eagle-Barrett syndrome

Epidemiology

  • Incidence: 1/35,000–50,000 live births
  • Most patients are detected during the neonatal period or prenatally during maternal ultrasound.
  • Prune belly syndrome is much more common in males (>95%). Females with urethral atresia may be affected.

Risk Factors

Genetics

  • The genetic basis of prune belly syndrome remains unclear.
  • Most patients have normal karyotypes.
  • Most cases are sporadic, although rare cases in sibs have been reported.
  • Genetic analysis of rare inherited forms have revealed homozygous mutations in the muscarinic acetylcholine receptor gene (CHRM3) and heterozygous mutations in α-smooth muscle actin (ACTA2), with sporadic forms rarely having mutations in hepatocyte nuclear factor 1β transcription factor (HNF1β).

Pathophysiology

The bladder in prune belly syndrome is large, irregularly shaped, and thick walled. Many patients have poor urinary flow and high residual volumes:

  • Ureters are usually markedly dilated, tortuous, and elongated. Peristalsis is ineffective, and the distal ureters are most severely affected. Vesicoureteral reflux is present in over 75% of cases.
  • Renal involvement is variable; the most severe dysplasia occurs in patients with extensive dilation of the urinary tract. Dysplastic changes are usually symmetric.
  • Usually, the bladder neck is wide and the prostatic urethra is dilated and triangular.

Etiology

The cause of prune belly syndrome remains unclear. Two theories have been proposed:

  • The triad of congenital defects may result from a primary mesodermal defect in development with congenital deficiency of smooth muscle in the bladder, ureter, and renal pelvis.
  • Outflow obstruction of the bladder in utero may result in dilation of the bladder and upper urinary tract with subsequent renal injury. The expanded bladder may block the route of the descending testicles and may cause abdominal distention and abdominal wall muscle atrophy.

Commonly Associated Conditions

Many patients have associated anomalies:

  • GI anomalies
    • Affect up to 25% of patients (e.g., imperforate anus, malrotation, gastroschisis, omphalocele, bowel atresia, and increased risk of volvulus)
  • Musculoskeletal anomalies
    • talipes equinovarus, congenital hip dislocation, pectus excavatum, scoliosis, hemivertebrae
  • Respiratory
    • Affect upward of 60% of patients (e.g., pulmonary hypoplasia, chronic respiratory tract infections due in part to impaired coughing, reactive airway disease, respiratory difficulty after general anesthesia)
  • Genital anomalies in females
    • genital sinus, urethral atresia, vesicovaginal fistula, vaginal atresia, and bicornuate uterus
    • Ovaries in affected female patients are typically normal.
  • Cardiac anomalies
    • Affect up to 25% of patients (e.g., patent ductus arteriosus [PDA], atrial septal defect [ASD], ventricular septal defect [VSD], tetralogy of Fallot [TOF])
  • Other genetic conditions
    • Children with trisomy 21 (Down syndrome) have an 11-fold increased risk of prune belly syndrome compared with other children.

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