An Overview of Hydronephrosis

An abnormal retention of urine can lead to kidney swelling and damage

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Hydronephrosis, or swollen kidney, occurs when urine backs up into one or both of the kidneys. Usually, urine flows from the kidneys to the bladder via the ureter. When a blockage or obstruction impedes the normal flow of urine, hydronephrosis can develop.

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The urinary tract serves two distinct purposes. The primary function of the kidneys is to filter out extra water, salt, and waste. The second is to collect and excrete urine from the body. If the system becomes blocked, urine can accumulate, causing the kidneys to swell. This is hydronephrosis.

When this impacts one kidney, it is called unilateral hydronephrosis; when both are affected, it’s called bilateral hydronephrosis. In most cases, only one kidney will be affected.

Initially, a person with hydronephrosis may not experience any noticeable signs of dysfunction. But, over time, symptoms may appear as the swelling persists, causing notable discomfort. The extent of the symptoms depends on the reason for the blockage and its severity.  

If not treated in a timely and appropriate manner, hydronephrosis can damage one or both kidneys and contribute to the development of acute or chronic kidney failure.


A person with hydronephrosis may not be aware they have the condition. When symptoms are present, they may show up within a range of hours, weeks, or months. Symptoms can include:

  • Flank pain
  • Pain during urination
  • Blood in the urine
  • Fever
  • Fatigue
  • Malaise
  • Nausea
  • Vomiting
  • Urinary tract infection (UTI)
  • A persistent urge to urinate
  • Changes in urinary frequency
  • Inability to void the bladder completely
  • Weak urine stream
  • Incontinence
  • Failure to thrive in infants

In extreme cases, the kidney swelling may be detectable by appearance or palpation (touch).


Hydronephrosis can affect people of all ages, from before birth to adulthood. If hydronephrosis happens before birth, it is referred to as antenatal hydronephrosis or fetal hydronephrosis.

Among infants and children, boys are twice as likely to experience hydronephrosis as girls. However, the condition does not appear to be inherently linked to genetics or family history.

Common risk factors for hydronephrosis in adults include renal calculi (kidney stones that cause blockage when they move adjacent to or into the drainage tube of the kidney, called the ureter), enlarged prostate, pelvic masses or tumors (such as ovarian cysts, cervical cancer, or prostate cancer), and neurogenic bladder (the neurological loss of bladder control).

Hydronephrosis can also occur during pregnancy as the developing fetus presses against the urinary tract.

Not all swelling of the kidney is hydronephrosis. If you have a normal variant to the shape of your kidney called extrarenal pelvis this may look like hydronephrosis on imaging. Further testing can be done to rule out real hydronephrosis versus having extrarenal pelvis. 


To diagnose hydronephrosis, you may be referred to a urologist for a series of tests and examinations. The most standard include the following.

  • Physical exam: The healthcare provider will take a detailed account of your symptoms and medical history and examine the kidney area. This will include a visual and manual exam to detect signs of kidney swelling or tenderness.
  • Imaging studies: The healthcare provider may use ultrasound, X-rays, computed tomography (CT), or magnetic resonance imaging (MRI) to see if your kidney is swollen and where the obstruction is occurring. Contrast dyes are sometimes used to visualize blood vessels and soft tissue masses.
  • Lab tests: Lab work may include a blood test to evaluate your kidney function (including urea and creatinine levels) and check if you could have an infection. You may also be asked to provide a specimen for a urinalysis to check for signs of an infection, blood, or kidney stones.

To ensure the correct diagnosis, the healthcare provider may perform other tests to exclude causes that are similar to hydronephrosis. The differential diagnoses may include multicystic dysplastic kidney (a congenital malformation of the kidneys), ureteroceles (a birth defect of the ureters that connect the kidneys to the bladder), or vesicoureteric reflux (a condition where urine backflows from the bladder to the kidneys), or extrarenal pelvis.


Although the treatment for hydronephrosis varies depending on the reason for the condition, in some cases, the situation resolves without the need for medical intervention. In mild to moderate cases, your healthcare provider may choose to wait and see if the condition improves on its own.

If your healthcare provider suspects a UTI or if you are at risk of developing one, they may prescribe you a course of antibiotics. If pain is an issue, you may also receive an over-the-counter or prescription nonsteroidal anti-inflammatory drug like ibuprofen or diclofenac.


Treating Kidney Stones

In severe cases of hydronephrosis, surgery may be needed to remove obstructions or redirect the flow of urine. Hydronephrosis caused by a restriction from where the kidney connects to the ureter (ureteropelvic junction) may warrant pyeloplasty (the surgical reconstruction of the kidney funnel system).

Other indications for surgery include persistent kidney pain with obstructing ureteral stone, urine infection with ureteral stone, kidney dysfunction, or recurrent UTI with a high fever.

If the hydronephrosis is related to an enlarged prostate, medications or surgeries will be done to reduce the size of the prostate.

Neurologic causes of hydronephrosis (such as a spinal cord injury that impairs bladder function) may require ongoing catheterization to help clear urine and anticholinergic drugs to increase bladder capacity.

Severe hydronephrosis can cause permanent kidney damage, but, in most cases, only one kidney will be harmed. Fortunately, one kidney is usually capable of doing the work of two.


When the cause of hydronephrosis is determined, there may be certain lifestyle modifications you can implement to lessen the chances of it happening again. For example, if you are prone to kidney stones, a specialized diet may help to avoid a recurrence of them.

As another example, if hydronephrosis is caused by urinary retention, muscle and nerve problems in the pelvis, or organ prolapse, pelvic floor therapy from a trained physical therapist or bladder catheterization can assist with retraining the bladder to work in a more normal way.

A Word From Verywell

Any medical diagnosis can be scary, but thankfully the prognosis for hydronephrosis is good when you seek appropriate medical treatment. If you develop a fever; sudden pain in the abdomen, side, or back; or any other symptoms of hydronephrosis, don’t wait to get the care you need—see your healthcare provider as soon as possible.

7 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Jenny Lelwica Buttaccio, OTR/L
Jenny Lelwica Buttaccio, OTR/L, is a licensed occupational therapist and advocate for patients with Lyme disease.