What it means
Each kidney gathers urine in a central space, the renal pelvis and its branches (calyces), before it drains down the ureter to the bladder. If the flow is slowed or blocked, urine backs up and this space widens. On ultrasound it shows as dark, fluid-filled branches in the middle of the kidney. Reports usually grade it as mild, moderate or severe.
When it matters
Mild hydronephrosis can be harmless. A very full bladder can cause it, and it may be gone on a scan after emptying. It is also common in pregnancy. Otherwise doctors look for a cause, such as a kidney stone, an enlarged prostate, a narrowing, or something pressing on the ureter. A long-lasting blockage can harm the kidney, and a blockage with fever needs urgent care. Next steps may include kidney blood tests, a CT or a kidney drainage scan.
Questions to ask your doctor
- How severe is the swelling, and is it on one side or both?
- What is causing the backup, and is it still there?
- Is my kidney function affected, and when should it be checked again?
