Hydronephrosis: Swelling of the Kidney
What hydronephrosis is — a kidney swollen by backed-up urine — and its causes.
Last updated: 2026-09-24
Hydronephrosis is swelling of a kidney caused by urine backing up when its drainage is blocked.
Common causes
- Kidney stones
- Tumours or strictures
- Pregnancy
- Enlarged prostate
Why it matters
Prolonged blockage can damage the kidney, so the cause is usually treated to relieve the backup.
Frequently asked questions
Does hydronephrosis always need surgery?
Not always — the treatment depends on the cause and severity.