POSTERIOR URETHRAL VALVES

Obstruction of the urethra by posterior urethral valves is the commonest (90%) cause of obstruction to the lower urinary tract occurring exclusively in males.
 

EMBRYOLOGY

Although the primary defect occurs in embryonic life, the age of onset and degree of urethral obstruction is highly variable.

 

ULTRASOUND

 

 

  • Male fetus.
  • Massive bilateral hydronephrosis.
  • Bilateral hydroureter.
  • Large hypertrophied urinary bladder. There may be visible repetitive contractions of the bladder (in an attempt to overcome the obstruction which leads to hypertrophy of the detrusor muscles proximal to the obstruction).
  • Dilated proximal urethra ("keyhole sign" = contiguous anechoic bladder and dilated posterior urethra may have a keyhole shape).

 

Case 1

28 weeks

Dilated bladder and posterior urethra (“keyhole sign”).

Dilated ureter

Male fetus

 

Case 2

 

 

 

Keyhole sign

 

 

  • Varying degrees of oligohydramnios and associated pulmonary hypoplasia.
  • Spontaneous decompression of the obstructed urinary system my occur at different points including:
    • The posterior urethra.
    • A renal calyx (paranephric pseudocyst or urinoma).
    • Through the urachus resulting in a urachal cyst or fistula.
    • Spontaneous bladder rupture (can result in ascites).
  • Cystic renal dysplasia may result from the persistent obstruction.
  • If bladder decompression does not occur either spontaneously or through vesicocentesis, the bladder will ultimately dilate, hypertrophy, and develop diverticuli, sacculation and trabeculation. Disruption of the ureterovesical sphincter and massive ureterovesical reflux. Renal parenchymal atrophy may result from the hydronephrosis and reflux.

 

 

 

Video Clip of post-natal voiding cystogram

 

 

 

 

ASSOCIATIONS
  • Chromosomal abnormalities (23%) (1).
    • Triploidy.
    • Trisomies 13 and 18.
    • del 2q.
  • Other genitourinary anomalies (20-25%).
    • Cryptorchidism.
    • Hypospadias.
    • Duplication of the urethra.
  • Cardiovascular anomalies, tracheal hypoplasia, scoliosis and imperforate anus.

 

 

REFERENCES
  1. Nicolaides KH, Rodeck CH, Gosden CM et.al. Rapid karyotyping in non lethal fetal malformations. Lancet 1986;1:283.