A 3 year old girl presents with recurrent UTI. On USG shows hydronephrosis with filling defect and negative shadow of bladder with no ectopic orifice-
**Core Concept**
The question tests the understanding of the anatomical and radiological features of a vesicoureteral reflux (VUR), a condition where urine flows backward from the bladder into the ureters, potentially leading to recurrent urinary tract infections (UTIs) and renal scarring.
**Why the Correct Answer is Right**
The presence of hydronephrosis and a filling defect in the upper urinary tract, along with a negative shadow of the bladder, suggests that the urine is leaking from the bladder into the ureters, causing the accumulation of urine in the renal pelvis and calyces. This is a classic radiological feature of VUR. The absence of an ectopic ureter orifice indicates that the reflux is likely due to a problem with the ureterovesical junction.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because an obstructed ureter would more likely cause an increase in ureteral diameter, rather than a filling defect.
**Option B:** This option is incorrect because a neurogenic bladder would typically cause a more diffuse loss of bladder control, rather than a localized issue like VUR.
**Option C:** This option is incorrect because a ureteral stone would cause a calcified shadow on the USG, rather than a filling defect.
**Option D:** This option is incorrect because an ectopic ureter would be visible on the USG as a separate ureteral orifice.
**Clinical Pearl / High-Yield Fact**
VUR is a common cause of recurrent UTIs in children, and early diagnosis and treatment can help prevent long-term renal damage.
**Correct Answer:**
**C**. Ureteral obstruction.