hydronephrosis
Meaning of hydronephrosis: Swelling of the drainage spaces is a clue rather than a diagnosis, and it can linger after the blockage that produced it has gone.
Definition of hydronephrosis
Hydronephrosis is swelling of the urine collecting spaces inside a kidney, the calyces and the renal pelvis, seen when urine cannot leave at the rate it arrives. Pressure builds behind the hold up and stretches those spaces, which is what shows on a scan. One or both kidneys may be affected, depending on where along the urinary tract the problem sits.
How hydronephrosis is built
- hydr/o Combining form · Greek water, fluid
- nephr/o, ren/o Combining form · Greek and Latin kidney
- -osis Suffix · Greek abnormal condition, increase
A medical term is read from its ending backwards: the suffix first, then the prefix, then the root. See all 223 word parts.
What blocks the flow?
| Where the problem sits | Usual causes | Kidneys affected |
|---|---|---|
| Where the kidney joins the ureter | Stone, a narrowing present from birth, scarring | One |
| Along the ureter | Stone, a tumor pressing from outside, surgical injury, scarring behind the abdomen | One |
| The bladder itself | Bladder tumor, or nerve damage leaving the bladder unable to empty | Often both |
| Below the bladder | Enlarged prostate, narrowing of the urethra, pelvic tumor | Both |
The side gives away the level. A blockage in one ureter can only swell one kidney, so swelling on both sides points below the bladder or to something pressing on both tubes at once. In children the commonest cause is a narrowing at the top of the ureter that was present from birth, often picked up before delivery on a routine scan.
Does it always mean a blockage?
No, and treating dilation and obstruction as the same thing is the usual error. Urine flowing backward from the bladder toward the kidney, called reflux, widens the same spaces with nothing blocking them. Pregnancy dilates the collecting system on both sides through a mix of pressure and hormonal relaxation, most often on the right, and it resolves afterward. A system stretched by a stone can stay baggy for a long time after the stone has passed. Very high urine output can also distend it briefly. Whether flow is actually obstructed is a separate question from whether the kidney looks swollen.
How is it found and why does it matter?
Ultrasound is the usual first look, since it needs no radiation and shows dilation clearly; further imaging then hunts for the cause and the level. Some cases turn up incidentally on a scan done for another reason, others during evaluation of flank pain, a urinary infection or a falling kidney function test. The concern is time. Pressure transmitted back into the filtering units gradually thins the kidney tissue, and function lost to prolonged obstruction may not return, which is why identifying what is blocking the flow takes priority over the swelling itself.
Used in a sentence
Imaging revealed hydronephrosis of the right kidney related to an obstructing stone.
Good to know
Hydronephrosis describes kidney swelling rather than a diagnosis in itself, and the swelling can persist after an obstruction has cleared, so evaluation centers on whether urine flow is actually blocked.
Word origin
Where “hydronephrosis” comes from
Formed from hydro-, Greek for water, and nephros, meaning kidney.