Medically Reviewed By William C. Lloyd III, MD, FACS
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What is hydronephrosis?

Hydronephrosis is an abnormal condition of the kidney. The kidneys are vital internal organs located in the upper abdomen. Normally, people have two bean-shaped kidneys, which form a part of the urinary tract in the genitourinary system.

Hydronephrosis occurs when an underlying disease, disorder or condition creates a partial or total obstruction or blockage of the ureter, the tube that carries urine from the kidney to the bladder. This results in pooling of urine in the kidneys accompanied by kidney swelling and distention. This problem more often involves just one kidney but it can affect both (bilateral). This is why affected individuals often have no early symptoms since the other kidney continues to function.

Hydronephrosis can also result from a condition that causes the abnormal reverse flow of urine from the bladder back up through the ureter into the kidney. Hydronephrosis can occur at any age, including in newborn infants born with the condition.

Hydronephrosis is a serious medical sign of a variety of conditions. Both hydronephrosis and its underlying causes can lead to kidney damage and deterioration of a kidney’s ability to perform functions that are critical to life and your overall health including:

  • Filtering waste products and excess water and salts from the blood, which are then eliminated from the body through the ureters, bladder and urethra in the form of urine

  • Producing certain hormones, such as renin, which helps regulate blood pressure

  • Producing the active form of vitamin D (calcitriol)

  • Regulating electrolytes and other vital substances, such as sodium, calcium and potassium

  • Regulating the level and quality of fluid in the body

  • Stimulating red blood cell production

Hydronephrosis can occur in one or both kidneys. It is especially serious if it occurs in both kidneys because of the potential for permanent damage to both vital organs and the risk of kidney failure.

Hydronephrosis is often caused by a serious underlying condition of the urinary tract. Rapid diagnosis and treatment of many underlying causes of hydronephrosis may prevent hydronephrosis altogether or prevent or slow the progression of serious kidney damage. Seek prompt medical care if you have unexplained symptoms, such as painful or frequent urination and nausea or vomiting.

Seek immediate medical (call 911) care if you, or someone you are with, have serious symptoms, such as shortness of breath, bloody or pink urine, decrease in urinating or lack of urine, severe flank or abdominal pain, or a change in consciousness or alertness.

What are the symptoms of hydronephrosis?

Symptoms of hydronephrosis and common coexisting conditions and underlying causes of hydronephrosis can vary. Sometimes there may be no symptoms at first. General symptoms may include:

  • Cloudy or discolored urine
  • Flank pain
  • Foul-smelling urine
  • High blood pressure
  • Palpable pelvic mass
  • Urgent urination

Symptoms that might indicate a serious or life-threatening condition

Hydronephrosis is often caused by a serious condition of the kidney or urinary tract, such as kidney stones. Seek immediate medical care (call 911) if you, or someone you are with, have any of the following symptoms:

  • Blood clots in urine or bloody urine (hematuria)

  • Change in consciousness, such as passing out or unresponsiveness

  • Change in mental status or sudden behavior change such as confusion

  • Decrease in urination or lack of urination

  • Severe flank pain that moves or radiates to the lower abdomen, groin, labia, or testicles

  • Shortness of breath or difficulty breathing

What causes hydronephrosis?

Hydronephrosis is caused by a variety of underlying diseases, disorders or conditions that obstruct or slow the flow of urine though the ureter, bladder or urethra. Hydronephrosis can also be caused by certain conditions that result in backflow of urine into the kidney. Your doctor’s goal is to determine the cause for the hydronephrosis and associated conditions. Causes include:

  • Bladder stone or tumors that block the flow of urine from the bladder, causing urine to back up into the ureters and kidneys

  • Blood clot

  • Congenital narrowing of the ureters or the ureter valves

  • Enlarged prostate

  • Kidney stone

  • Neurogenic bladder (bladder that does not empty due to nerve damage)

  • Pregnancy

  • Tumor or cancer of the ureter that presses and impinges on the ureter. A tumor or cancer of the uterus, intestine, or other area can also press on the ureter.

  • Ureter scarring due to injury or surgery

  • Ureteropelvic junction obstruction (UPJ, a blockage in the area where the kidney connects to the ureter; UPJ can be present at birth or caused by scarring due to infection, kidney stone, or surgery)

  • Urethral stricture (scarring of the urethra, which can block the flow of urine from the bladder, causing urine to back up into the ureters and kidneys)

  • Vesicoureteral reflux (condition in which urine flows backward up the ureters and into the kidney)

What are the risk factors for hydronephrosis?

A number of factors increase the risk of developing hydronephrosis. Risk factors include:

  • Blood clotting disorders

  • Cancer in the pelvic or lower abdominal area

  • Enlarged prostate

  • Frequent urinary tract infections

  • Neurogenic bladder (damaged bladder nerves)

  • Pregnancy

  • Urinary tract or pelvic organ surgery

Reducing your risk of hydronephrosis

Not all people who are at risk for hydronephrosis will develop the condition. However, you can lower your risk of developing hydronephrosis by seeking prompt medical care for urinary symptoms, such as frequent urination, painful urination, and difficulty urinating.

How is hydronephrosis treated?

Treatment of hydronephrosis varies greatly depending on the underlying cause of disease. Treatment can include:

  • Antibiotics to prevent or treat a urinary tract infection

  • Nephrostomy tube (a tube inserted through the back) to drain fluid from the kidney

  • Placement of a special tube (stent) in the ureter

  • Reduction or elimination of certain medications or foods, such as protein shakes, that can be hard on the kidneys

  • Surgical or endoscopic procedures to correct an obstruction or other abnormalities

  • Treatment of the underlying cause of hydronephrosis. For example, kidney stones are treated with fluids, pain medications, and surgery if necessary.

What are the potential complications of hydronephrosis?

Hydronephrosis and its underlying causes can lead to serious and even life-threatening complications. Following the treatment plan you and your health care provider develop specifically for you will minimize the risk of complications including:

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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2021 Jan 18
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THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
  1. Bilateral hydronephrosis. PubMed Health, a service of the NLM from the NIH. http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001506/.
  2. Kidney Stones. National Kidney Foundation. http://www.kidney.org/atoz/content/kidneystones.cfm.
  3. Kidney Stones in Adults. National Kidney and Urologic Diseases Information Clearinghouse. http://kidney.niddk.nih.gov/kudiseases/pubs/stonesadults/.
  4. Kidney Disease. Lab Tests Online. http://www.labtestsonline.org/understanding/conditions/kidney-2.html.
  5. UPJ obstruction. Medline Plus, a service of the National Library of Medicine National Institutes of Health. http://www.nlm.nih.gov/medlineplus/ency/article/001267.htm.
  6. Your Child Has Hydronephrosis. National Kidney Foundation. http://www.kidney.org/atoz/content/hydronephrosis.cfm.
  7. Unilateral hydronephrosis. PubMed Health, a service of the NLM from the NIH. http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001535/.
  8. Taal MW, Chertow GM, Marsden PA, et al. (Eds.)  Brenner and Rector's The Kidney, (9th ed.). New York: Elsevier, 2011.
  9. Domino FJ (Ed.) Five Minute Clinical Consult. Philadelphia: Lippincott Williams & Wilkins, 2013.