In a patient with left renal agenesis and right hydronephrosis, what is the best step to prevent progression?

• A. Insert a right percutaneous nephrostomy tube (proximal obstruction)
• B. Place a urinary catheter (distal obstruction) if signs are present
• C. Observation only
• D. Surgical nephrectomy

Answer: (A)

When only one kidney remains, any obstruction there can rapidly damage renal function, so the priority is to relieve the obstruction promptly. Right hydronephrosis signals upstream blockage; decompressing the collecting system lowers intrarenal pressure, preserves glomerular filtration, and helps prevent irreversible kidney injury. A percutaneous nephrostomy tube provides rapid drainage of urine from the obstructed kidney, making it the best initial step. A urinary catheter wouldn’t address proximal obstruction, observation risks ongoing damage, and removing the kidney would sacrifice the sole functioning organ.