**Core Concept**
The patient's presentation of fever, dysuria, and gross hematuria, along with a suprapubic mass and dullness on percussion, suggests a diagnosis related to an obstructive uropathy or a urinary tract anomaly. This condition is commonly seen in children and is often associated with a palpable abdominal mass.

**Why the Correct Answer is Right**
The clinical presentation is consistent with a diagnosis of **Posterior Urethral Valve (PUV)**, a congenital anomaly of the male urethra. In PUV, a membrane or valve-like structure obstructs the posterior urethra, leading to urinary retention, obstructive uropathy, and potentially severe complications if left untreated. The presence of a palpable suprapubic mass and dullness on percussion is likely due to a distended bladder secondary to the obstruction.

**Why Each Wrong Option is Incorrect**
**Option A:** **Glomerulonephritis** is unlikely in this case, as the urinalysis reveals red blood cells but no proteinuria, which is more characteristic of glomerular disease. Additionally, the presence of a palpable suprapubic mass and dullness on percussion is not typical of glomerulonephritis.
**Option B:** **Pyelonephritis** may present with fever and dysuria, but it is less likely to cause a palpable suprapubic mass and dullness on percussion. Furthermore, the urinalysis would likely show proteinuria and pyuria, which are not mentioned in the case.
**Option C:** **Ureteropelvic Junction Obstruction (UPJO)** is a possible cause of obstructive uropathy, but it is less likely to present with a palpable suprapubic mass and dullness on percussion. UPJO is often associated with hydronephrosis, which is not mentioned in the case.

**Clinical Pearl / High-Yield Fact**
The presence of a palpable suprapubic mass and dullness on percussion in a child with fever, dysuria, and hematuria should raise suspicion for an obstructive uropathy, such as posterior urethral valve. This condition requires prompt evaluation and treatment to prevent long-term renal damage.

**Correct Answer:** C. Ureteropelvic Junction Obstruction (UPJO)