Hydronephrosis

What is hydronephrosis?

Hydronephrosis is a condition in which one or both kidneys become swollen because urine cannot drain away normally and builds up inside the kidney. The word comes from Greek roots meaning “water in the kidney.” It is not a disease in itself, but rather a sign that something is blocking or slowing the flow of urine somewhere in the urinary tract — the system made up of the kidneys, the ureters (the narrow tubes that carry urine from each kidney to the bladder), the bladder, and the urethra (the tube through which urine leaves the body).

When urine backs up, pressure rises inside the kidney’s collecting system, the funnel-shaped area where urine gathers before flowing down the ureter. If the pressure continues for a long time, it can stretch the kidney tissue and gradually reduce how well the kidney filters waste from the blood. When only one kidney is affected, doctors call it unilateral hydronephrosis; when both kidneys are affected, it is bilateral hydronephrosis.

Hydronephrosis can affect people of any age. It is often detected before birth on routine pregnancy ultrasounds, where it is one of the more common findings; in many of these babies the swelling improves on its own after birth. In adults, it is frequently linked to kidney stones, an enlarged prostate in men, pregnancy, or narrowing of the urinary tract. Because the causes and the seriousness vary so widely, understanding what is hydronephrosis in your specific situation depends on identifying what is blocking the urine flow and how severe the blockage is.

Symptoms of hydronephrosis

Hydronephrosis symptoms depend heavily on how quickly the blockage develops, how severe it is, and whether one or both kidneys are involved. Some people — especially those with mild swelling that develops slowly — have no symptoms at all, and the condition is found by chance on a scan done for another reason.

When symptoms do occur, they may include:

• Pain in the side or back (flank pain) — often between the ribs and hip, which may spread toward the lower abdomen or groin. Pain from a sudden blockage, such as a kidney stone, can be severe and come in waves.
• Nausea and vomiting — common when the pain is intense.
• Changes in urination — needing to urinate more often, urgency, a weak stream, difficulty starting, or feeling that the bladder does not empty completely.
• Blood in the urine (hematuria) — the urine may look pink, red, or brown.
• Urinary tract infection signs — burning with urination, cloudy or foul-smelling urine, fever, or chills. Infection in a blocked kidney can become serious quickly.
• Reduced urine output — especially if both kidneys are blocked or a person has only one functioning kidney.
• Swelling or a feeling of fullness in the abdomen in some cases of long-standing, severe hydronephrosis.

The pattern of symptoms often reflects the type of blockage. Acute hydronephrosis — a blockage that develops suddenly, as with a stone lodged in the ureter — typically causes sharp, severe pain. Chronic hydronephrosis — swelling that builds up gradually, for example from a slowly growing prostate or a narrowing of the ureter — may cause only a dull ache, vague discomfort, or no pain at all, even when the kidney is significantly stretched. Babies and young children with hydronephrosis usually show no obvious symptoms; the condition is most often picked up on prenatal or routine ultrasound scans, though some children develop urinary infections, poor feeding, or irritability.

Causes and risk factors

Hydronephrosis causes fall into two broad groups: something physically blocking the urinary tract (obstruction), or urine flowing backward from the bladder toward the kidney (a condition called vesicoureteral reflux). Common causes include:

• Kidney stones — hard deposits of minerals that can lodge in the ureter and block urine flow. This is one of the most frequent causes of sudden hydronephrosis in adults.
• Enlarged prostate — in men, the prostate gland surrounds the urethra; when it enlarges with age (benign prostatic hyperplasia), it can slow or block urine leaving the bladder, causing urine to back up.
• Ureteropelvic junction (UPJ) obstruction — a narrowing where the kidney’s collecting system joins the ureter. This is often present from birth and is a common cause of hydronephrosis in infants and children.
• Vesicoureteral reflux — a condition, most often seen in children, in which urine flows backward from the bladder up the ureters toward the kidneys.
• Pregnancy — the growing uterus can press on the ureters, and pregnancy hormones relax the muscle in their walls. Mild hydronephrosis during pregnancy is common and usually resolves after delivery.
• Ureteral strictures — scarring and narrowing of the ureter after infection, previous surgery, radiation therapy, or injury.
• Tumors — growths in the bladder, ureter, prostate, cervix, colon, or nearby structures can press on or grow into the urinary tract.
• Blood clots or debris inside the urinary tract.
• Nerve or muscle problems affecting the bladder — sometimes called neurogenic bladder, in which the bladder does not empty properly because of conditions such as spinal cord injury, diabetes, or multiple sclerosis.

Risk factors reflect these causes. People with a history of kidney stones, older men with prostate enlargement, pregnant women, people who have had pelvic surgery or radiation, and those with certain cancers are at higher risk. In babies, hydronephrosis usually results from how the urinary tract formed before birth rather than anything the parents did or could have prevented.

Diagnosis of hydronephrosis

Hydronephrosis diagnosis usually starts with a medical history and physical examination. Your doctor may ask about pain, urinary habits, past stones or infections, and pregnancies or surgeries, and may gently press on your abdomen and back to check for tenderness or a swollen kidney.

Imaging is the key to confirming hydronephrosis, because the swelling itself can only be seen on a scan:

• Ultrasound — usually the first test. It uses sound waves (no radiation) to show whether the kidney’s collecting system is dilated (widened). Doctors often grade the swelling from mild to severe based on how stretched the collecting system appears. Ultrasound is also the standard tool for detecting hydronephrosis before birth and for monitoring it in children and during pregnancy.
• CT scan (computed tomography) — a detailed X-ray-based scan that is particularly good at finding kidney stones and identifying exactly where and why the urinary tract is blocked in adults.
• MRI (magnetic resonance imaging) — sometimes used when radiation should be avoided or when soft tissues need closer evaluation.
• Renal scan (nuclear medicine scan) — a test that uses a small amount of a tracer substance to measure how well each kidney works and how quickly urine drains. It helps doctors decide whether a blockage is significant enough to need surgery, especially in children.
• Voiding cystourethrogram (VCUG) — an X-ray test performed while the bladder fills and empties, used mainly in children to check for vesicoureteral reflux.

Alongside imaging, doctors typically order urine tests to look for infection or blood, and blood tests — such as creatinine, a waste product filtered by the kidneys — to check overall kidney function. In some cases, a urologist (a surgeon who specializes in the urinary tract) may look inside the bladder with a thin camera, a procedure called cystoscopy, to find the cause of a blockage. Because hydronephrosis is a finding rather than a final diagnosis, the goal of testing is always twofold: confirm the swelling, and identify what is causing it.

Treatment options for hydronephrosis

Hydronephrosis treatment depends on the cause, the severity, whether one or both kidneys are affected, how well the kidneys are working, and whether infection is present. The overall goals are to relieve the pressure on the kidney, treat the underlying cause, and protect kidney function. An overview of how this condition is managed is available on the hydronephrosis treatment page.

Watchful waiting

Not every case needs immediate intervention. Mild hydronephrosis — particularly in newborns and infants, and mild cases during pregnancy — often improves on its own. In these situations, doctors may recommend regular ultrasound scans to monitor the kidney over time, stepping in only if the swelling worsens or kidney function is threatened. Some children with reflux or mild obstruction are given low-dose antibiotics to help prevent urinary infections while the urinary tract matures, depending on the individual situation.

Medication

Medicines do not remove a physical blockage, but they play several supporting roles. Antibiotics treat urinary tract infections, which is especially important when a kidney is blocked. Pain relievers help manage the discomfort of stones or acute swelling. In men with an enlarged prostate, medications that relax or shrink the prostate may improve urine flow and reduce back-pressure on the kidneys. Certain medicines may also be used to help small ureteral stones pass on their own, when a doctor judges this to be safe.

Drainage procedures

When pressure on the kidney needs to be relieved quickly — for example, when there is severe blockage, worsening kidney function, or infection behind the obstruction — doctors can drain the urine using one of two main approaches:

• Ureteral stent — a soft, thin tube placed through the bladder into the ureter, allowing urine to flow past the blockage from the kidney to the bladder. It is usually inserted through the urethra without external incisions and is often temporary.
• Nephrostomy tube — a small tube inserted through the skin of the back directly into the kidney, draining urine into an external bag. This is typically used when a stent cannot be placed or when the kidney needs urgent decompression.

These procedures relieve pressure but do not fix the underlying cause, so further treatment usually follows.

Surgery and definitive treatment of the cause

Once the kidney is protected, treatment focuses on the underlying problem. Kidney stones may be broken up with shock waves (lithotripsy), removed through a small telescope passed up the ureter (ureteroscopy), or, for large stones, removed through a small incision in the back. A congenital narrowing at the ureteropelvic junction can be corrected with a reconstructive operation called pyeloplasty, which removes the narrowed segment and rejoins the healthy ends; this is frequently done with minimally invasive (laparoscopic or robotic) techniques. Prostate enlargement that blocks urine flow may be treated with medication or with procedures that open the channel through the prostate. Strictures of the ureter can be dilated, stented, or surgically repaired, and tumors are managed according to the specific cancer involved. In rare cases where a kidney has been severely and permanently damaged and causes ongoing problems such as pain or infection, removal of the kidney (nephrectomy) may be discussed, provided the other kidney works well.

Care for hydronephrosis often involves both urologists and nephrologists — physicians who specialize in kidney function and kidney disease. At Acibadem, long-term kidney health aspects of this condition are managed within the Nephrology Department, working alongside urology when procedures or surgery are needed.

Living with hydronephrosis and outlook

The outlook for hydronephrosis varies widely and depends mainly on the cause, how severe the blockage is, how long it has been present, and whether one or both kidneys are involved. In many cases the outlook is good: when the blockage is relieved promptly — for example, after a stone passes or is removed — the kidney usually recovers, and swelling often resolves without lasting damage. Hydronephrosis related to pregnancy typically improves after delivery, and mild hydronephrosis found before birth frequently resolves on its own during infancy.

When a significant blockage goes untreated for a long time, however, the kidney can lose function, and in severe cases that loss may be permanent. This is why follow-up matters. If you have been diagnosed with hydronephrosis, your care team may recommend periodic ultrasounds, urine tests, and blood tests to track kidney function over time, even after treatment. People with a history of kidney stones may be advised to drink plenty of fluids and make dietary changes to reduce the chance of new stones, and men with prostate-related symptoms benefit from ongoing review of their urinary function.

Day to day, most people who have been treated for hydronephrosis can live normally. Practical steps that support kidney health in general include staying well hydrated unless your doctor advises otherwise, treating urinary infections promptly, managing conditions such as diabetes and high blood pressure, and attending scheduled follow-up appointments. Because every situation is different, honest conversations with your doctor about your specific cause and kidney function are the best guide to your personal outlook — no general article can predict an individual outcome.

Frequently asked questions

What is hydronephrosis in simple terms?

Hydronephrosis means a kidney is swollen because urine is not draining out of it properly and is building up inside. It is a sign of an underlying problem — such as a kidney stone, a narrowing in the urinary tract, or pressure from an enlarged prostate or pregnancy — rather than a disease on its own. Finding and treating the cause is the central part of care.

How serious is hydronephrosis?

It ranges from mild and harmless to potentially serious. Mild swelling, especially when found in babies or during pregnancy, often resolves without treatment. A severe or long-standing blockage, or a blocked kidney with infection, can damage the kidney and needs prompt medical attention. Only a doctor, using imaging and kidney function tests, can judge how serious a particular case is.

Can hydronephrosis go away on its own?

In some situations, yes. Mild hydronephrosis detected before birth frequently improves as a child grows, pregnancy-related swelling usually settles after delivery, and small kidney stones may pass by themselves, allowing the kidney to return to normal. In other cases — such as a fixed narrowing or a large stone — the swelling will not resolve until the blockage is treated. Monitoring with ultrasound helps doctors tell the difference.

What are the first symptoms of hydronephrosis?

Early hydronephrosis symptoms, when present, often include aching or sharp pain in the side or back, changes in urination such as urgency or a weak stream, and sometimes blood in the urine or signs of infection. Many people, however, have no symptoms at all in the early stages, particularly when the swelling develops slowly, which is why the condition is often discovered on scans done for other reasons.

What happens if hydronephrosis is left untreated?

If a significant blockage is not relieved, ongoing pressure can gradually damage kidney tissue and reduce kidney function, and in severe long-standing cases the affected kidney may stop working. A blocked kidney that becomes infected can lead to a serious, rapidly worsening infection. Because early treatment usually protects the kidney, delays are best avoided once a meaningful blockage has been identified.

What is the recovery like after hydronephrosis treatment?

Recovery depends on the treatment. After stent placement or stone procedures, many people go home the same day or after a short stay, though a stent can cause temporary urinary discomfort until it is removed. Reconstructive operations such as pyeloplasty involve a longer recovery, often several weeks, especially for a full return to strenuous activity. Follow-up imaging is commonly used afterward to confirm that the kidney is draining well.

Is hydronephrosis in babies dangerous?

Usually not. Hydronephrosis is one of the more common findings on prenatal ultrasounds, and in many babies the swelling is mild and improves on its own during the first months or years of life. Doctors typically monitor affected infants with repeat ultrasounds and sometimes additional tests. A minority of children — generally those with more severe blockage or reflux — need medication or surgery to protect the developing kidney.

When to see a doctor

Talk with a doctor if you have persistent pain in your side or back, ongoing changes in urination, or blood in your urine, or if hydronephrosis has been found on a scan and you have not yet had it evaluated. Seek urgent medical care right away if you experience any of the following red-flag warning signs:

• Severe, unrelenting pain in your side, back, or abdomen, especially with nausea or vomiting.
• Fever or chills along with flank pain or urinary symptoms — this can signal infection in a blocked kidney, which is a medical emergency.
• Little or no urine output, or a sudden inability to urinate.
• Visible blood in the urine, particularly with pain or clots.
• Known hydronephrosis with worsening symptoms, such as new pain, fever, or swelling.
• Only one functioning kidney and any new flank pain or urinary problem, since a blockage in a single kidney can affect overall kidney function quickly.

Prompt evaluation allows doctors to relieve pressure on the kidney early, treat infection, and address the underlying cause — the steps most likely to preserve kidney function and prevent complications.