Investigation of choice to demonstrate vesico-ureteric reflex:
**Core Concept**
The vesico-ureteric reflex (VUR) is a pathophysiological process where the filling of the bladder with urine leads to a retrograde flow of urine into the ureters, often resulting in urinary tract infections and renal scarring. This phenomenon is closely related to the anatomy and physiology of the lower urinary tract.
**Why the Correct Answer is Right**
The investigation of choice to demonstrate VUR is the **voiding cystourethrogram (VCUG)**. This imaging study involves the introduction of a contrast agent into the bladder, which is then visualized during urination. The VCUG allows for the direct visualization of the ureters and bladder, enabling the detection of any retrograde flow of urine. The mechanism of VUR is closely related to the incompetent ureterovesical junction, where the normal antireflux mechanism is disrupted, allowing urine to flow back into the ureters.
**Why Each Wrong Option is Incorrect**
* **Option A:** Ultrasonography is not the investigation of choice for demonstrating VUR, although it may be used to detect hydronephrosis, a potential consequence of VUR.
* **Option B:** Cystoscopy is a diagnostic tool that allows for the visualization of the bladder and urethra, but it does not provide information on the ureteral anatomy or the presence of VUR.
* **Option C:** Computed tomography (CT) urography is a more recent imaging modality that can provide detailed images of the upper urinary tract, but it is not the primary investigation for VUR.
**Clinical Pearl / High-Yield Fact**
The VCUG is a crucial investigation for diagnosing and managing VUR, especially in children, as it helps guide the decision for surgical intervention to prevent long-term renal damage.
**Correct Answer:** C. Computed Tomography (CT) urography