**Question:** Most important investigation for posterior urethral valve is –

A. Urodynamic study
B. Ultrasonography
C. Voiding cystourethrogram (VCUG)
D. Urethrogram

**Core Concept:** Posterior urethral valves (PUV) are a congenital abnormality where valves form within the posterior wall of the urethra, causing obstruction and subsequent complications in children.

**Why the Correct Answer is Right:** The most important investigation for diagnosing PUV is Voiding Cystourethrogram (VCUG). VCUG combines the benefits of both cystography and voiding cystourethrogram, enabling the visualization of the urinary bladder, urethra, and the upper urinary tract during the voiding phase. This helps in assessing the obstruction, dilation, and any associated renal scarring.

**Why Each Wrong Option is Incorrect:**

A. Urodynamic study: While urodynamics assesses the function of the lower urinary tract, it does not specifically evaluate for PUV obstruction.
B. Urethrogram: A urethrogram focuses on imaging the urethra and penile structure, but it does not provide information about bladder function or upper tract involvement.
C. Voiding cystourethrography: Voiding cystourethrography focuses on bladder imaging during the filling phase, not providing detailed information about urethral obstruction or renal involvement.

**Clinical Pearl:** PUV is a critical diagnosis for early intervention, as prompt treatment can prevent progressive renal damage. VCUG is the gold standard for diagnosing PUV and assessing its severity.