What causes Keyhole sign in urinary tract on VCUG?
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Answer:
Keyhole sign is a focal funnel or keyhole-shaped dilatation of the posterior urethra seen on voiding cystourethrogram (VCUG) due to posterior urethral valves (PUV), a congenital obstructive uropathy in male infants presenting with bilateral hydronephrosis, thick-walled trabeculated bladder, poor urinary stream, urinary tract infections, and renal impairment.
Why is it called so?
Named for the characteristic keyhole appearance on voiding cystourethrogram (VCUG), resembling a classic keyhole with a dilated posterior urethra forming the round upper part and the narrow anterior urethra forming the slit-like lower part.
Pathophysiology
Posterior urethral valves are ectopic mucosal folds acting as a diaphragm-like obstruction in the posterior urethra, causing obstruction to urine outflow during voiding; this leads to ballooning and funnel-shaped dilatation of the posterior urethra proximal to the valve while the distal urethra remains narrow, producing the Keyhole sign configuration on VCUG.
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