Okay, let's tackle this question about vesicoureteral reflux (VUR). The question is asking which diagnostic test demonstrates VUR. The options aren't provided, but I need to figure out the correct answer based on standard medical knowledge.

First, I need to recall what VUR is. It's when urine flows backward from the bladder into the ureters and kidneys, which can lead to infections and kidney damage. The core concept here is the diagnostic method used to confirm this condition.

The main diagnostic tests for VUR include voiding cystourethrography (VCUG) and renal ultrasound with DMSA scan. VCUG is the gold standard. During this procedure, a catheter is inserted into the bladder, and contrast dye is instilled while X-rays are taken during urination. This allows visualization of the urinary tract and any backward flow of urine.

Now, considering the options, if one of them is VCUG, that's the correct answer. Let's see the wrong options. Other tests like renal ultrasound can show hydronephrosis but not the reflux itself. DMSA scan assesses renal scarring, not the presence of VUR. Cystoscopy might be used for visual inspection but isn't the primary test for VUR. Ultrasound alone isn't sufficient for diagnosing VUR.

Clinical pearl: VCUG is the gold standard for diagnosing VUR, but it's invasive. Less invasive options like radionuclide cystography are alternatives, especially in children. Remember that DMSA is for assessing renal scarring, not the reflux itself.

Putting it all together: The correct answer should be VCUG. So, if option C is VCUG, then the correct answer is C. The other options are incorrect for the reasons mentioned.

**Core Concept**
Vesicoureteric reflux (VUR) is the retrograde flow of urine from the bladder to the ureters/kidneys. The diagnostic gold standard involves imaging during bladder filling and voiding to visualize abnormal retrograde flow.

**Why the Correct Answer is Right**
Voiding cystourethrography (VCUG) is the definitive test for VUR. It involves instilling contrast into the bladder via a catheter while obtaining fluoroscopic images during voiding. This directly visualizes ureteral reflux by detecting contrast moving back into the ureters/kidneys. It also assesses urethral anatomy and voiding dynamics.

**Why Each Wrong Option is Incorrect**
**Option A:** Renal ultrasound detects hydronephrosis or bladder wall changes but cannot visualize actual reflux.
**Option B:** DMSA scan evaluates renal cortical scarring and function but does not detect VUR.
**Option D:** Cystoscopy inspects the bladder and urethra but cannot assess retrograde flow during voiding.

**Clinical Pearl / High-Yield Fact**
VCUG is invasive but remains the gold standard for VUR diagnosis. Non-invasive alternatives like radionuclide cystography are preferred in children for radiation avoidance. DMSA is used post-VUR to assess renal scarring.

**Correct Answer: C. Voiding cystourethrography**

✓ Correct Answer: B. Tc-99 - DMSA