**Core Concept**
Pyelonephritis and cystitis are common urinary tract infections (UTIs) in children, but the presentation of fever, dysuria, and gross hematuria with a suprapubic mass suggests a specific condition.

**Why the Correct Answer is Right**
This presentation is classic for a **urinary tract obstruction**, particularly a **urinary tract stone** or **posterior urethral valve**. The suprapubic mass is likely a distended bladder due to the obstruction. The presence of red blood cells in the urine without proteinuria suggests a lower urinary tract issue, such as a stone or valve, rather than pyelonephritis or glomerulonephritis.

**Why Each Wrong Option is Incorrect**
**Option A:** Pyelonephritis typically presents with flank pain, fever, and costovertebral angle tenderness, rather than a suprapubic mass.

**Option B:** Glomerulonephritis can cause hematuria and proteinuria, but the absence of proteinuria in this case makes it less likely.

**Option C:** Ureteropelvic junction obstruction can cause hydronephrosis and renal impairment, but it typically presents with abdominal pain and a palpable mass in the flank.

**Clinical Pearl / High-Yield Fact**
In children, a suprapubic mass with dysuria and hematuria is highly suggestive of a urinary tract obstruction, such as a stone or posterior urethral valve. Always consider these conditions in the differential diagnosis of a child with these symptoms.

**Correct Answer:** C.