"My health check report says hydronephrosis. Is it serious?" "Is a swollen kidney the same as water on the kidney?" These are questions urologists hear often. Hydronephrosis, sometimes called a swollen or water-filled kidney, all describe one situation: the part of the kidney that collects urine stretches and swells because urine cannot drain.
Normally urine is made in the kidney, flows down the ureter to the bladder and leaves through the urethra. If anything along this path is blocked by a stone, an enlarged prostate, a tumour or scar tissue, or if urine flows backwards, urine can build up in the kidney and cause hydronephrosis.
Hydronephrosis may cause only mild discomfort or no symptoms at all, but if the blockage continues, kidney function can be harmed. This article covers the common causes, symptoms and tests for hydronephrosis, and when to seek care quickly. If your main concern is pain in the side or back, see also flank and side pain.
Key points: Hydronephrosis is not a single disease. It means urine is blocked or flows backwards on its way from the kidney to the bladder and urethra, so the urine-collecting part of the kidney swells. Common causes in adults include kidney stones, an enlarged prostate, pregnancy, and blockage from tumours or scar tissue. Many people have no symptoms and it is found on a health check ultrasound. If you have flank pain with fever or chills, pass much less urine, or cannot pass urine, seek care promptly; with early treatment most people recover.
What Is Hydronephrosis? Symptoms of a Swollen Kidney
Hydronephrosis can affect one kidney or both. A sudden blockage, such as a stone in the ureter, often causes obvious flank pain; a blockage that develops slowly may cause no symptoms until an ultrasound finds it.
Common symptoms include pain in the lower back, side or belly, needing to pass urine often or having difficulty passing it, cloudy urine, blood in the urine, nausea and vomiting, and fever or chills. For changes in urine colour, see abnormal urine colour.
Mild hydronephrosis on a health check ultrasound: should I worry?
Mild hydronephrosis is sometimes linked to holding urine, scanning with a very full bladder, or drinking a lot of water, and it may disappear on a repeat scan after passing urine. It can also be an early sign of blockage. Take the report to a urologist to decide whether more tests are needed rather than ignoring it.
Hydronephrosis in pregnancy or on a fetal ultrasound
During pregnancy the growing womb can press on the ureters and cause hydronephrosis in the mother, which usually improves after delivery. Hydronephrosis found in a baby on a pregnancy ultrasound is also fairly common and often improves during pregnancy or after birth; a few babies need follow-up or treatment, so follow the plan from the obstetric and paediatric urology teams.
What Causes Hydronephrosis?
In adults, hydronephrosis is commonly caused by kidney or ureteral stones blocking the urine passage. In men it is also often linked to an enlarged prostate blocking the bladder outlet so that the bladder does not empty fully.
Other causes include urinary tract infection or inflammation, narrowing of the ureter from scar tissue after injury or surgery, blood clots, pressure from bladder or pelvic tumours, and a neurogenic bladder that cannot empty normally. In children, a congenital narrowing where the kidney meets the ureter, or urine flowing back from the bladder to the kidney (vesicoureteral reflux), is more common.
Can holding urine or drinking too little water cause hydronephrosis?
Holding urine for long periods or poor bladder emptying can make urine back up, and drinking too little can raise the risk of stones, which may cause a blockage indirectly. However, hydronephrosis usually has a definite cause of blockage or reflux that needs to be found with tests, so adjusting how much you drink is not a substitute for assessment.
| Possible cause | Common groups or situations | Possible clues |
|---|---|---|
| Kidney or ureteral stones | History of stones, low fluid intake | Sudden severe flank pain, blood in the urine, nausea |
| Enlarged prostate or bladder outlet blockage | Middle-aged and older men | Straining to pass urine, incomplete emptying, passing urine at night, often both sides |
| Pregnancy | Pregnant women, mid to late pregnancy | Usually mild, improves after delivery |
| Congenital blockage or vesicoureteral reflux | Fetuses, infants and children | Found on pregnancy ultrasound, or repeated urinary tract infections |
| Scar tissue, tumour or blood clot | Previous surgery or radiotherapy, history of tumours | Develops slowly, may cause no symptoms |
What Tests Are Done for Hydronephrosis?
The doctor will ask about pain, passing urine and fever, any history of stones or surgery, and whether you might be pregnant, and will examine you. Men may have a rectal examination to check whether the prostate is enlarged.
Ultrasound and imaging
Kidney and bladder ultrasound shows how severe the hydronephrosis is and whether the bladder empties. It uses no radiation and is a common first test. To find where the blockage is, the doctor may arrange a CT scan, an MRI scan or a nuclear medicine kidney scan to assess the blockage and how well each kidney works.
Blood tests, urine tests and cystoscopy
Blood tests check kidney function, and a urine test can show infection or blood in the urine. If a bladder or urethra problem is suspected, the doctor may also arrange a cystoscopy. If you also have burning when passing urine, see painful urination.
| Test | Main purpose | Notes |
|---|---|---|
| History and physical exam | Understand symptoms, past history and possible pregnancy | Bring previous health check and imaging reports |
| Kidney and bladder ultrasound | Assess the degree of hydronephrosis and bladder emptying | No radiation, can be repeated for follow-up |
| Blood and urine tests | Assess kidney function, infection and blood in the urine | A urine culture is often needed when there is fever |
| CT or MRI scan | Find where the blockage is and what causes it | Decided by the doctor based on symptoms and kidney function |
| Nuclear medicine kidney scan, cystoscopy | Assess each kidney’s function, examine the bladder and urethra | Arranged when needed |
How Is Hydronephrosis Treated, and What Can You Do Day to Day?
Treatment depends on the cause and severity. If the blockage is significant, there is infection, or kidney function is falling, the doctor usually drains the urine first, for example with a urinary catheter, a ureteral stent (double-J stent) or a nephrostomy tube through the skin, to relieve pressure on the kidney.
After drainage, the cause is treated, for example stone surgery, medicines or surgery for an enlarged prostate, antibiotics for infection, or repair of a narrowing. If you cannot pass urine, see urinary retention (Chinese page). For mild hydronephrosis with no sign of blockage, the doctor may suggest regular ultrasound follow-up.
For daily care, drink a suitable amount of water as advised by your doctor, avoid holding urine for long periods, and stay active. If you have had stones, discuss diet and fluid changes with your doctor. If you have heart or kidney disease and need to limit fluids, follow your doctor’s advice and do not drink large amounts on your own.
Can drinking more water or supplements help hydronephrosis?
Self-treatment is not recommended. If the urine passage is already blocked, drinking a lot may make the swelling and pain worse, and supplements cannot remove a blockage. Find the cause first, then follow your doctor’s advice.
When to Seek Care Quickly for Hydronephrosis
Hydronephrosis needs its cause found, so see a doctor if you have related symptoms or it shows up on a health check. Seek care promptly or go to an emergency department if you have:
Pain in the side or lower back with fever, chills or shivering.
Much less urine than usual, or you cannot pass urine at all.
Severe flank pain with nausea or vomiting that does not ease with pain relief.
Flank pain or a change in urine output if you have only one kidney, a kidney transplant or known poor kidney function.
Flank pain with fever, or painful urination, during pregnancy.
It depends on the cause. Mild hydronephrosis in pregnancy or in a fetus often improves on its own, and it may settle after a stone passes. But an ongoing blockage can harm kidney function, so follow up as your doctor advises rather than judging it yourself.
When hydronephrosis is treated early, most people recover without long-term problems. But a blockage that lasts a long time or is severe can damage kidney function, so the cause should be found promptly once it is discovered.
Yes, these terms describe the same situation: urine cannot drain, so the urine-collecting part of the kidney swells. A report may grade it as mild, moderate or severe; leave the interpretation to your doctor.
No. Hydronephrosis is urine building up inside the kidney and is a urinary blockage problem. Swollen legs or puffy eyelids may be related to the heart, kidney function or other conditions and need separate assessment.
The interval depends on the cause, severity and kidney function, and your doctor will arrange it. If you develop flank pain, fever, less urine or blood in the urine during follow-up, do not wait for your appointment; seek care earlier.
See a urologist. Pregnant women can also discuss it with their obstetrician, and fetuses or children are followed by paediatric urology. If you have flank pain with fever or cannot pass urine, go to an emergency department.
Medical references
- NHS: Hydronephrosis
- MedlinePlus (U.S. National Library of Medicine): Bilateral hydronephrosis
- National Kidney Foundation (NKF): Hydronephrosis
- European Association of Urology (EAU): Guidelines on Urolithiasis
- European Association of Urology (EAU): Guidelines on Paediatric Urology
Advice from the urologist
- If a health check finds hydronephrosis, take the report to a urologist to work out the cause and follow-up rather than ignoring it.
- If you have flank pain with fever or chills, pass much less urine, or cannot pass urine, seek care promptly or go to an emergency department.
- The key to managing hydronephrosis is finding and relieving the blockage; drinking large amounts on your own or buying supplements is not recommended.
- People with a history of stones or an enlarged prostate benefit from regular follow-up and not holding urine for long, which helps catch changes early.
Hydronephrosis sounds alarming, but it is really a warning that something is wrong somewhere along the urine passage. Most causes can be found with ultrasound and related tests, and early treatment usually protects kidney function. If you have flank pain, a change in urine output, or hydronephrosis on a health check, I recommend an assessment by a urologist in person.
