A boy with a thick-walled bladder, bilateral hydroureteronephrosis and a dilated posterior urethra (keyhole sign antenatally) — the voiding MCUG shows the valve and the dilated posterior urethra, and ultrasound shows the renal damage.
Orient first
- The commonest cause of lower urinary tract obstruction in boys.
- Antenatal: keyhole bladder, oligohydramnios, echogenic kidneys (poor prognosis).
- Urinary ascites and perirenal urinoma act as pop-off valves that may protect a kidney.
Acquire the study
- Curvilinear probe; kidneys, ureters, bladder; transperineal view of the posterior urethra.
The manoeuvre
- Bladder wall thickness in mm; trabeculation.
- Bilateral hydroureteronephrosis — APRPD in mm.
- Renal parenchyma: echogenicity and cortical cysts (dysplasia).
- Transperineal plane: dilated posterior urethra.
What confirms it
- Dilated posterior urethra with a calibre change on voiding MCUG.
What licenses you to exclude it
- A normal voiding urethra on MCUG excludes valves.
The classic misread
- Missing valves in a boy with unilateral findings.