Prune Belly Syndrome (Early urethral obstruction sequence)

• Early urethral obstruction sequence results most commonly from urethral valve formation, but it can be due to urethral atresia or more distal urethral obstructions. The obstruction may also be functional. Because the most common etiology of the disorder is malformed development of the penile urethra, it is most common in males (95%)

• The disorder occurs most commonly as a sporadic event and is associated with a low recurrence risk for future pregnancies.

Sequence:

• Urethral obstruction -> enlarged bladder and oligohydramnios

• Accumulation of urine in the fetal bladder and urinary system beginning at about 8 weeks of gestation, when urine formation begins.

• Enlarged bladder

  • hydroureter and renal dysplasia. Renal dysplasia can range from mildly affected kidneys with near normal function to severely hypoplastic/dysplastic kidneys. Hydronephrosis and massively dilated ureters are present. Often have VUR, bladder dysfunction, and recurrent UTIs.

  • Male cryptorchidism due to failure of the testes to descend because of pressure from the enlarged bladder.

  • compression of abdominal contents: +/- malrotation of colon

  • compression of iliac vessels: disrupt blood flow to the lower extremities, leading to limb deficiency.

• Abdominal distension: excess of abdominal skin and a deficiency of abdominal musculature

• Oligohydramnios deformation complex

  • including hypoplastic lungs

  • breech presentation

  • altered facial features

  • abnormal positioning of the hands and feet

Severe obstruction is fatal in fetal life unless the urinary bladder is decompressed. This can occur in utero though rupture. In some centers, prenatal decompression of the bladder by vesicoamniotic shunt placement, which also increases amniotic fluid volume to promote lung development, has been attempted. Infants who are born alive frequently have renal damage, although the abdominal musculature usually develops postnatally.

Prognosis correlates with extent of renal dysplasia. Severe dysplasia associated with maternal oligohydraminios and pulmonary hypoplasia results in perinatal demise in 20% of cases.

Chronic amniotic fluid leakage and renal agenesis result in the oligohydramnios sequence, which causes pulmonary hypoplasia and fetal compression. However, prune belly is not an associated feature because the bladder is not distended. Extrophy of the bladder refers to exposure of the bladder due to failure of the infra-umbilical mesoderm to invade the cloacal membrane. Polycystic kidneys do not cause an obstructive uropathy, although in some cases they are associated with oligohydramnios.

References:
CHLA Board Review 2005
Freedman AL, Johnson MP, Smith CA, Gonzalez R, Evans MI. Long-term
outcome in children after antenatal intervention for obstructive
uropathies. Lancet. 1999;354:374-377
Jones KL. Smith's Recognizable Patterns of Human Malformation. 5th ed.
Philadelphia, Pa: WB Saunders Co; 1997:622-623