Hydronephrosis
Read Your Scan Editorial Team·Last updated
Written from published radiology references and reviewed for plain language. Not written or signed by a physician, and not a diagnosis. How we write these pages →
In plain language
Swelling of the kidney’s collecting system because urine is not draining freely. The report grades it as mild, moderate or severe; the cause, often a stone, is what determines what happens next.
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Where you'll see this
This wording turns up on Abdominal CT reports — CT imaging of the abdomen. An abdominal CT shows the liver, gallbladder, pancreas, spleen, kidneys, bowel, blood vessels, and lymph nodes in fine detail. Doctors order it for abdominal pain, to look into a suspected stone, infection, or blockage, or to check known findings. Because it is so detailed, it often notes small, harmless things by chance. The report describes what the images show; your doctor reads it together with your symptoms and other results.
Questions worth asking your doctor
- What was the main reason for this CT, and did it answer that question?
- Were any findings incidental, and do any of them need follow-up?
- If a stone or cyst was seen, does it need treatment or monitoring?
- Do the results change my current care or medications?
- Is there anything I can do about findings like fatty liver?
How common is this?
Hydronephrosis is a common finding on abdominal CT and ultrasound, particularly on scans done for sudden flank pain, where a stone is the usual explanation. The word describes the kidney’s collecting system swelling because urine is not draining away freely — pressure builds behind whatever is in the way. Reports grade it mild, moderate or severe, and often add whether one or both sides are involved, which itself points towards different causes.
When should I worry?
The grade matters less than the cause and the duration. Blockage with an infection is the situation that needs urgent attention: fever, chills or feeling systemically unwell alongside flank pain is a combination to act on the same day rather than wait out. Severe pain that will not settle, vomiting, or passing little or no urine are also reasons to be seen promptly. Mild hydronephrosis found incidentally on someone with no symptoms is a very different matter and is often long-standing or of no consequence — including in pregnancy, where a degree of it is normal.
What happens next
The work goes into finding what is obstructing rather than treating the swelling itself. For a stone, that often means pain control and time, since many pass on their own, with a procedure reserved for stones that do not. Where infection is present alongside obstruction, drainage is arranged urgently. Where no stone is found, the search moves to other causes of narrowing, and a follow-up scan checks that the kidney has decompressed once the obstruction is dealt with.
Frequently asked questions
- Is mild hydronephrosis serious?
- Often not. Mild dilatation can be long-standing, can follow a stone that has already passed, and is a normal finding in pregnancy. What makes any grade serious is infection alongside it, or obstruction left in place long enough to affect kidney function — which is why the cause is investigated rather than the grade treated.
- What usually causes hydronephrosis?
- A kidney stone is the commonest cause in adults with sudden pain. Other causes include narrowing where the ureter joins the kidney or bladder, pressure from outside the ureter, and in men an enlarged prostate obstructing outflow, which typically affects both sides.
- Can hydronephrosis damage my kidney permanently?
- It can if a significant obstruction is left untreated for a long period, which is exactly why the cause is pursued rather than watched. Relieved reasonably promptly, kidney function usually recovers. Short-lived obstruction from a stone that passes rarely causes lasting harm.
Other words on the same report
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