Hydronephrosis
Hydronephrosis is the swelling of one or both kidneys caused by a buildup of urine. This occurs when urine cannot flow normally from the kidney to the bladder due to a blockage or obstruction. Hydronephrosis may develop suddenly or gradually and can range from mild to severe. Some people have no symptoms, while others experience pain, infections, or impaired kidney function.
What is it?
Hydronephrosis occurs when urine backs up into the kidney, causing it to stretch and swell. This may happen when something blocks the ureter (the tube that carries urine to the bladder) or when the bladder doesn’t empty properly. Causes include kidney stones, ureteral strictures, tumors, enlarged prostate, pregnancy-related compression, and congenital abnormalities.
Imaging helps determine whether the hydronephrosis is mild or severe, whether one or both kidneys are affected, and what the underlying cause may be. Ultrasound is usually the first test, while CT or MRI can provide more detail. Renal scans may be used to evaluate how well the kidneys are functioning.
Important to Know
Hydronephrosis is a finding—not a disease itself. The underlying cause determines the urgency and type of treatment. Some mild cases resolve on their own, especially when due to temporary swelling or recent stone passage. More severe or long-standing hydronephrosis can damage the kidney over time.
Red flag symptoms include severe flank pain, fever, nausea or vomiting, inability to urinate, or blood in the urine. These may indicate infection or a significant blockage and require urgent evaluation. Follow-up imaging may be recommended to confirm improvement or monitor kidney function.