Hydronephrosis: What Causes Kidney Swelling, How It Is Found, and How It Is Treated
Updated: 3 days ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 2026
Hydronephrosis is swelling of one or both kidneys caused when urine builds up instead of draining away, often because of a blockage or a condition present at birth [1]. It frequently causes no symptoms, but side and back pain, painful or urgent urination, fever, vomiting, or blood in the urine should prompt a doctor's visit. Diagnosis uses blood tests, urine tests, and imaging such as ultrasound or CT urogram. Treatment targets the cause and may include pain medicine, antibiotics, drainage, or surgery — and early treatment helps prevent lasting kidney damage [2].
Quick Answer
Hydronephrosis is swelling of one or both kidneys that happens when urine cannot drain and builds up inside. It is most often caused by a blockage in the tubes to the bladder or a difference present at birth. Many people have no symptoms, though some have side pain or fever. Treatment depends on the cause and may include surgery.
What the research says
Milder antenatal hydronephrosis usually stabilizes or improves. A meta-analysis of studies of children with isolated hydronephrosis found before birth showed that the dilated kidney drainage system stabilized or improved in 98% of those with milder grades (SFU grades 1–2) and in 51% of those with higher grades (3–4). Milder cases were about five times more likely to stabilize (odds ratio 4.69; 95% CI 1.73 to 12.76) (Sidhu et al., Pediatr Nephrol, 2006 [3]).
Evidence for preventive antibiotics in babies is limited. A systematic review of 11 studies with 3,909 infants with antenatal hydronephrosis found similar urinary tract infection rates in non-randomized studies whether or not continuous antibiotic prophylaxis was used (9.9% with antibiotics versus 7.5% without). The authors judged the data to be of very low quality and suggested antibiotics may still be of value in high-grade hydronephrosis (Easterbrook et al., Can Urol Assoc J, 2017 [4]).
What Is Hydronephrosis?
Hydronephrosis happens when urine builds up in a kidney. Often, a blockage called an obstruction in the upper part of the urinary tract causes the buildup, and kidney swelling can result. This causes the part of the kidney called the renal pelvis to bulge, or become distended. Over time, it could lead to kidney scarring, and the kidney may not work as well as it should.
In simple terms, hydronephrosis is swelling of one or both kidneys. It happens when urine cannot drain from a kidney and builds up inside it as a result. The condition can be caused by a blockage in the tubes that drain urine from the kidneys, and it can also happen because of a difference present at birth that prevents urine from draining properly. In some people, hydronephrosis causes kidney damage over time.
The condition can happen at any age, and it often causes no symptoms at all. Tests to find it can be done during infancy, and sometimes even before a baby is born. Treatment depends on the underlying cause: some people need medicine or surgery to feel better and prevent kidney damage, while mild hydronephrosis sometimes goes away on its own over time.
Key fact | What it means |
Definition | Swelling of one or both kidneys when urine builds up instead of draining |
How it forms | Urine cannot drain, so the renal pelvis bulges and the kidney swells |
Who it affects | People of any age, including babies before birth |
Symptoms | Often none; pain, fever, vomiting, or blood in urine when present |
Main risk | Lasting kidney damage, and rarely kidney failure, if untreated |
Symptoms: What Does Hydronephrosis Feel Like?
Hydronephrosis often causes no symptoms. But when symptoms do happen, they can include the following.
Symptom | How it may appear |
Side and back pain | Pain in the side and back that may travel to the lower stomach area or groin |
Urinary symptoms | Pain with urination, or feeling a need to urinate that is urgent or happens often |
Stomach symptoms | Upset stomach and vomiting |
Fever | Elevated temperature, which in a baby warrants an immediate checkup |
Infant symptoms | Failure to thrive in infants |
General symptoms | Weight loss or loss of appetite |
Urine changes | Blood in urine |
When to See a Doctor
Call your healthcare professional if you have any symptoms of hydronephrosis. Get emergency care right away for fever or chills with side or back pain, or if you cannot urinate, because a blocked and infected kidney needs urgent treatment. Babies with the condition often do not have symptoms. However, you should get your baby a healthcare checkup right away for symptoms such as high fever.
Situation | What to do |
Any side/back pain, fever, or urinary symptoms | Call your healthcare professional |
Baby with high fever | Get a checkup right away |
Baby diagnosed prenatally | Follow the imaging follow-up plan given by the care team |
How the Urinary System Works
Understanding hydronephrosis starts with the urinary system, which includes the kidneys, ureters, bladder, and urethra. The urinary system removes waste from the body through urine. The kidneys sit toward the back of the upper belly and filter waste and fluid from the blood to make urine. Urine moves from the kidneys to the bladder through narrow tubes called the ureters. The bladder stores urine until it is time to urinate, and urine leaves the body through a small tube called the urethra.
What Causes Hydronephrosis?
Causes of hydronephrosis include a blockage or another health issue that affects the urinary tract, which includes the kidneys and the bladder. A partly or fully blocked urinary tract can keep urine from leaving the kidneys and cause swelling. Other issues that disrupt the urinary tract can cause urine to flow backward through the ureters from the bladder up into the kidneys. When urine flows the wrong way, the condition is called vesicoureteral reflux.
The known causes fall into seven categories.
Cause | How it leads to hydronephrosis |
Conditions present at birth | A partial kidney blockage called ureteropelvic junction obstruction, most often where a kidney attaches to a ureter; or an atypical ureter structure causing vesicoureteral reflux |
Kidney stones | Hard buildups of minerals and salts that form inside the kidneys and can block drainage |
Enlarged prostate | A very enlarged prostate can cause the bladder to have trouble emptying, so urine may back up into the kidneys |
Injured or narrowed ureter | Pelvic surgery through the stomach area can injure a ureter by accident; narrowing can follow surgical scarring or radiation therapy for prostate cancer |
Urinary tract infection | Infection can inflame any part of the urinary tract, including the kidneys |
Pregnancy | Swelling of the kidneys' urine drainage system is common during pregnancy; it often causes no symptoms and goes away after giving birth |
Cancer | A tumor can cause a urinary tract blockage, including from bladder, cervix, colon, or prostate cancers |
Risk Factors
Risk factors differ by age group. Among adults ages 20 to 60, being born female raises risk. The higher risk could be due to certain conditions that affect the uterus, such as pregnancy, and could also be due to conditions that affect the ovaries, such as cysts, buildups of pus, and cancer. Risk factors for people older than age 60 include having an enlarged prostate or a urinary tract blockage from cancer.
Age group | Risk factors |
Adults ages 20–60 | Being born female; conditions affecting the uterus (such as pregnancy) or the ovaries (such as cysts, buildups of pus, and cancer) |
Adults over 60 | Enlarged prostate; urinary tract blockage from cancer |
Possible Complications
Hydronephrosis can lead to other health conditions called complications. Without treatment, some people who have severe hydronephrosis develop lasting kidney damage. Rarely, the condition can cause an affected kidney to lose its ability to filter blood, which is called kidney failure.
How Is Hydronephrosis Diagnosed?
Diagnosis involves the steps your healthcare team takes to find out whether hydronephrosis is the cause of your symptoms. Your healthcare professional starts by asking about your symptoms and doing a physical exam. You may be referred to a doctor called a urologist, who finds and treats conditions of the urinary system.
Several tests can help find out whether you have hydronephrosis.
Test | What it checks |
Blood test | Checks how well the kidneys work |
Urine test | Looks for clues that infection or kidney stones may be causing a blockage |
Ultrasound imaging exam | Views the kidneys, bladder, and other parts of the urinary tract; can help spot possible health conditions |
CT urogram | An X-ray of the urinary tract that uses special dye to outline the kidneys, ureters, bladder, and urethra; captures images before and after urination |
Your healthcare professional may also suggest another imaging exam, such as an MRI. Another testing option called a MAG3 scan checks kidney function and drainage. During pregnancy, a routine ultrasound test often spots hydronephrosis in unborn babies.
Treatment Options
Treatment for hydronephrosis depends on its cause and how bad the symptoms are. The goal of treatment is to ease kidney swelling and prevent kidney damage. You may need medicine, a process to drain urine, or surgery. In some people, mild hydronephrosis goes away on its own in time.
Medications
Your healthcare professional may prescribe medicine to ease pain. Some people need medicine called antibiotics to clear up a urinary tract infection. Sometimes, babies with hydronephrosis are given antibiotics to prevent infections. Babies often do not need other treatment because they often have mild hydronephrosis that gets better on its own, and imaging tests can track their health over time.
Surgery and Other Procedures
Sometimes, surgery is needed to fix a blockage or correct the backward flow of urine. Surgery also may be done to ease terrible pain or vomiting from hydronephrosis. It can be a treatment option when the condition is caused by kidney stones, an enlarged prostate, a blocked or narrowed ureter, or cancer.
Some people also need to have excess urine drained from the body. A healthcare professional does this by placing a thin tube called a catheter into the bladder.
Treatment path | When it is used |
Pain medicine | To ease pain while the cause is addressed |
Antibiotics | To clear a urinary tract infection, or in babies to prevent infections |
Drainage (catheter) | To remove excess urine from the body through a thin tube placed into the bladder |
Surgery | To fix a blockage or correct backward urine flow, ease severe pain or vomiting, or treat stone, prostate, ureter, or cancer-related causes |
Watchful waiting with imaging | For babies and mild cases, which often improve on their own |
Early treatment for hydronephrosis helps many people get better and also helps prevent lasting kidney damage.
Coping With Hydronephrosis
A hydronephrosis diagnosis can bring worry about kidney health, especially when imaging and treatment plans stretch over weeks or months. Babies often have mild cases that improve on their own with imaging follow-up, while adults may need one or more procedures to address the underlying cause. Talking openly with your healthcare professional about what to expect from each test, what the treatment goals are, and what symptoms should trigger a call to the office can make the process feel more manageable. Bringing a family member or friend to appointments can help you remember the information you are given.
Preparing for Your Appointment
You may start by seeing your main healthcare professional, or you might be referred to a urologist who finds and treats urinary tract conditions.
What You Can Do
When you make the appointment, ask whether there is anything you need to do in advance. For instance, you may need to stop eating for a certain number of hours before a test. It also helps to make a list covering the following areas.
List item | What to include |
Your symptoms | All symptoms, including any that do not seem related to the reason for the appointment |
Key personal information | Major stresses, recent life changes, and family medical history |
Medicines and supplements | All medicines, vitamins, and other supplements you take, including the doses |
Questions to ask | A written list of questions for your healthcare professional |
Take a family member or friend along if you can. This person can help you remember the information you are given.
For hydronephrosis, some basic questions to ask your healthcare professional include: What is likely causing my symptoms, and are there other possible causes? What tests do I need? Is my condition likely short-term or long lasting? What treatment is right for me, and are there other treatment choices? If I have other health conditions, how can I best manage them together? Are there restrictions I need to follow? Should I see a specialist? Are there brochures or other printed material I can have, and what websites do you recommend?
What to Expect From Your Doctor
Your healthcare professional is likely to ask questions such as the following.
Doctor's likely question | Purpose |
When did your symptoms start? | Establish the timeline |
Do your symptoms happen some of the time or all of the time? | Gauge frequency |
How bad are your symptoms? | Gauge severity |
What, if anything, seems to make your symptoms better? | Identify relieving factors |
What, if anything, appears to make your symptoms worse? | Identify aggravating factors |
Conclusion: Find the Cause Early and Protect the Kidneys
Hydronephrosis is a descriptive condition rather than a disease in itself: it tells you that urine is backing up into a kidney, and the job of the care team is to find out why. Because it often causes no symptoms, it can be discovered on routine prenatal ultrasound or during testing for other urinary problems. When symptoms do appear — side and back pain, painful or urgent urination, fever, vomiting, weight loss, or blood in the urine — a timely medical evaluation matters.
The good news is that diagnosis is straightforward with blood tests, urine tests, and imaging, and treatment is tailored to the cause, ranging from simple watchful waiting in babies to antibiotics, drainage, or surgery in others. Early treatment helps most people get better and protects the kidneys from lasting damage.
Take the next step: If you or your child has any of the warning signs above, schedule an appointment with a healthcare professional and ask about kidney imaging.
Frequently Asked Questions
What is hydronephrosis?
Hydronephrosis is swelling of one or both kidneys that happens when urine cannot drain from a kidney and builds up inside it. It is usually caused by a blockage in the urinary tract or a condition present at birth, and it can happen at any age.
Does hydronephrosis have symptoms?
Often there are no symptoms at all. When symptoms do occur, they can include side and back pain that may travel to the lower stomach or groin, painful or urgent urination, upset stomach and vomiting, fever, failure to thrive in infants, weight loss, or blood in the urine.
When should I seek care for hydronephrosis symptoms?
Call your healthcare professional if you have any hydronephrosis symptoms. Babies often have no symptoms, but you should get your baby a healthcare checkup right away for symptoms such as high fever.
What causes hydronephrosis?
Causes include conditions present at birth (ureteropelvic junction obstruction or vesicoureteral reflux), kidney stones, an enlarged prostate, an injured or narrowed ureter, urinary tract infection, pregnancy, and tumors from certain cancers such as bladder, cervix, colon, or prostate cancer.
What is vesicoureteral reflux?
Vesicoureteral reflux happens when urine flows backward through the ureters from the bladder up into the kidneys. It can occur when a baby is born with a ureter that is not typical in structure, and it can cause hydronephrosis.
Can hydronephrosis cause kidney damage?
Yes, if it is not treated. Some people with severe hydronephrosis develop lasting kidney damage, and rarely an affected kidney can lose its ability to filter blood, a condition called kidney failure.
How is hydronephrosis diagnosed?
Diagnosis starts with a symptom review and physical exam, often with referral to a urologist. Tests include a blood test for kidney function, a urine test for infection or stones, ultrasound imaging, and sometimes a CT urogram, MRI, or a MAG3 scan that checks kidney function and drainage.
Can hydronephrosis be found before birth?
Yes. During pregnancy, a routine ultrasound test often spots hydronephrosis in unborn babies.
How is hydronephrosis treated?
Treatment depends on the cause and symptom severity, with the goal of easing kidney swelling and preventing kidney damage. Options include pain medicine, antibiotics, draining excess urine through a catheter, or surgery to fix a blockage or correct backward urine flow.
Do babies with hydronephrosis need surgery?
Babies often have mild hydronephrosis that gets better on its own and does not need other treatment. Imaging tests track their health over time, and some babies are given antibiotics to prevent infections.
Does hydronephrosis go away during pregnancy?
Swelling of the kidneys' urine drainage system is common during pregnancy. It often causes no symptoms and goes away after giving birth.
Is early treatment important?
Yes. Early treatment for hydronephrosis helps many people get better and helps prevent lasting kidney damage.
Related Reading
Ureteral Stent: Why It's Used, Placement, Side Effects and Removal explains ureteral stents and what to expect.
Nephrostomy Tube: Purpose, Placement and Care explains nephrostomy tubes and how to care for them.
Learn more in our guide to Extracorporeal Shock Wave Lithotripsy (ESWL): Procedure, Recovery, Risks and Results.
Kidney Ultrasound: Why It's Done, How to Prepare and What It Shows explains the radiation-free imaging test used to look for stones, cysts, blockages and other kidney problems.
Renal Scan (Kidney Scan): Types, Preparation, Risks and Results explains the nuclear medicine scan used to measure kidney function, blood flow and blockages.
Voiding Cystourethrogram (VCUG): Why It's Done, What to Expect and Reflux Grades explains the X-ray test used to diagnose urine reflux in children.
Renal MAG3 Scan: Kidney Function and Drainage Test Explained explains the nuclear scan that shows how well the kidneys work and drain.
References
Mayo Clinic Staff. Hydronephrosis - Symptoms and causes. Mayo Clinic. November 6, 2024. https://www.mayoclinic.org/diseases-conditions/hydronephrosis/symptoms-causes/syc-20575276
Mayo Clinic Staff. Hydronephrosis - Diagnosis and treatment. Mayo Clinic. November 6, 2024. https://www.mayoclinic.org/diseases-conditions/hydronephrosis/diagnosis-treatment/drc-20575279
Sidhu G, Beyene J, Rosenblum ND. Outcome of isolated antenatal hydronephrosis: a systematic review and meta-analysis. Pediatr Nephrol. 2006;21(2):218-224. PMID 16362721. https://doi.org/10.1007/s00467-005-2100-9
Easterbrook B, Capolicchio JP, Braga LH. Antibiotic prophylaxis for prevention of urinary tract infections in prenatal hydronephrosis: an updated systematic review. Can Urol Assoc J. 2017;11(1-2Suppl1):S3-S11. PMID 28265307. https://doi.org/10.5489/cuaj.4384
Further reading: National Kidney Foundation. Hydronephrosis. National Kidney Foundation. August 8, 2023. https://www.kidney.org/kidney-topics/hydronephrosis; NHS. Hydronephrosis. NHS. July 17, 2025. https://www.nhs.uk/conditions/hydronephrosis/.
Medical disclaimer
This article is for educational purposes only and does not replace professional medical advice. Always consult a qualified healthcare provider for diagnosis and treatment.
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