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What is Hydronephrosis?

Mary McMahon
Updated May 17, 2024
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Hydronephrosis is a medical condition characterized by a distention of the kidney caused by a buildup of urine which cannot be evacuated through the bladder. This condition can become quite dangerous, and it can also cause a variety of health problems, including long-term atrophy of the kidney as a result of the stretching caused by hydronephrosis. There are a number of causes for this condition, along with an assortment of treatment approaches.

Urine will back up into the kidneys if there is an obstruction in the urinary tract. This can be caused by a structural abnormality, compression of the urinary tract, or by movement of the kidney which causes a kink to develop, much like the kink in a hose. Obstructions such as tumors and kidney stones are also a common cause of the condition. Whatever the cause, urine will slowly start to pool in the kidney, eventually causing it to distend with the pressure of the fluid inside.

This condition can be characterized as unilateral, meaning that one kidney is involved, or bilateral, in which case both kidneys are affected. Bilateral hydronephrosis tends to cause more severe symptoms, which include decreased urination, pain, and tenderness in the abdomen. In extreme cases, the kidney may be so swollen that it is palpable on a physical examination.

In acute hydronephrosis, the blockage and swelling occur quickly, causing a rapid onset of symptoms. Chronic hydronephrosis takes longer to develop into a serious problem, and it can be caused by a partial blockage which simply slow drainage from the kidney, rather than bringing it to a halt. Both require medical attention so that the blockage can be identified and corrected.

Medical imaging such as ultrasound can often reveal a hydronephrosis situation, and the doctor may also use urine samples and bloodwork to test kidney function. Catheterization and more invasive procedures may be performed in an attempt to determine the cause and to clear the blockage. In some cases, surgery may be required to correct the problem which caused the condition, while in other instances, it may be possible to remove the blockage with less invasive techniques.

If something like a tumor is causing the condition, additional treatments may be needed to prevent recurrence. The kidneys may also need supportive therapy if the condition has been allowed to remain untreated for a prolonged period, with treatments like dialysis being used to give the kidneys a chance to recover.

WiseGeek is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Mary McMahon
By Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a WiseGeek researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Discussion Comments
By anon976037 — On Oct 30, 2014

I have a situation where an X-ray radiologist says I have an 18mm ureter stone. A subsequent ultrasound shows the associated kidney to be 63 percent larger than the other. My urologist says this is normal and is pooh-poohing the first X-ray. Is this size difference within the normal size difference for kidneys? I see no references anywhere to kidney volume size differences related to hydronephrosis swelling.

By anon948778 — On May 01, 2014

My two year child is suffering from renal swelling 10mm and every report is normal. All passages are clear. Is it dangerous or not?

By anon258039 — On Mar 30, 2012

After an ultrasound it was found that I have one atrophied kidney and the other one has a distended renal pelvis which is also an extra renal pelvis in the compensating kidney. None of the medical staff seem to think this is urgent, even though I have pain and am worried that there is damage being made to the remaining kidney.

I personally think that action should be taken to preserve my kidney function immediately, and progression should be prevented. This was discovered a year ago and I am waiting yet another two months to see the urologist and another three months to see the neurologist. Is this all too long?

By anon244205 — On Jan 31, 2012

"The left kidney demonstrates mild hydronephrosis without ureterectasis." What does this mean? What is the treatment? Please tell me the answer.

By anon232620 — On Dec 01, 2011

My husband had a renal ultrasound done, and his results show:

Right renal cysts: 1.1 x 1.0 x 1.0 cm, 9 x 7 x 11mm.

Left renal cysts: 1.5 x 1.1 x 1.0 cm.

Left renal calcification. No hydronephrosis, perinephric fluid or mass.

Impression: No hydronehprosis bilaterally. Left renal calculus 7mm.

Two right renal cysts. One left renal cyst, measurements as above. Cholelithiasis.

What does all that mean?

By anon175128 — On May 12, 2011

I felt extreme pain in my right kidney, and the following is the ultrasound result.

"Both kidneys are of normal sizes and outlines having normal echogenicity. Right sided mild hydronephrosis with proximal hydroureter- Suggestive of distal obstruction." Please explain to me what does the above result mean?

By anon156553 — On Feb 28, 2011

In the ultrasound result they told me that from my baby's right kidney only 20 percent of urine is being passed and the rest is blocked. can this be cured before birth? should it be treated?

By anon116341 — On Oct 06, 2010

I read on my medical notes that 10 years ago after tests I have hydronephrosis yet I have never been told this or had any treatment or interventions? How can this be?

By anon76786 — On Apr 12, 2010

When i was pregnant they noticed my little boy had bilaterial hydronephrosis and since then he has been on an antibiotic all of his two years of life. The hospital said his tubes coming from his kidneys are both too large at the top.

He is due back into see the consultant next month and I'm not to sure what to expect because both of the kidneys are getting worse. Is there anyone out there who has been through this that can share their story with me?

By anon73714 — On Mar 29, 2010

my brother(12 years old now) had an operation of tumor on his left kidney one and half years back, and now again a tumor has developed at the same place. what could be the reasons for it? as it is growing at a fast speed, the doctor says that it needs to be removed as soon as possible. will this keep on repeating?

By anon58890 — On Jan 05, 2010

my husband had an ultrasound done and the results are as follows

A cystic colletion neasuring 3.53cm x 2.86cm was seen in the right kidney. There was mld loss of corticomedullary differentiation in both kidneys.

Right kidney measured 10.6cm in length

Left kidney measured 10.5 cm in length.

The prostate gland appeared normal volume 12ml. The walls of the urinary bladder were thickened 1.06cm. Urinary bladde3r volume=317ml. Post micturition volume=12ml


- Bilateral renal parenchymal disease. No hydronephrosis seen.

-right renal cyst.

- Cystitis. No significant residual volume seen.

- Normal sonographic appearances of the prostate gland.

Could you explain?

By anon56610 — On Dec 16, 2009

what is the treatment for mild hydronephrosis?

By anon41799 — On Aug 17, 2009

How did you find out what type of cyst you have? What tests did you have done? My doctor wants to do an MRI with contrast dye and I have read so many detrimental things about kidney failure being caused from the dye that I am afroad to have the tests. I also have uretrocele but the doctor thinks i have hydronephrosis also which could be caused by a blockage such as a tumor, cyst, or a kidney stone. I believe your cyst may be the cause of your hydronephrosis. Hydronephrosis is when the kidney does not empty all the urine and becomes enlarged, and could become damaged. There are different things that can cause this condition. If it is a stone they will simply dissolve it. Sometimes surgery is needed if the cyst might be the cause.

By anon28309 — On Mar 14, 2009

Good day!

Well i have a problem. This afternoon i received my ultrasound result findings: Slightly enlarged right kidney hydronephrosis, Bilateral,cortical cyst, lower pole of the right kidney. mild uretero-hydronephrosis, left, residual urine. Can you pls explain to me what this is and what is the treatment. thanks

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a...

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