Pyonephrosis is a kidney obstruction caused by infection and the formation of pus ("pyon" in Greek), which can result in rapid and complete loss of kidney function. Because the pus is thicker than urine, it blocks the passage of urine and results in the formation of an abscess. Although the condition is rare, it has been reported in adults, children, and even newborns.

If pyonephrosis is diagnosed and treated promptly, the affected kidney usually recovers within 24 to 28 hours. If treatment is delayed, however, the kidney can be permanently injured by the development of fistulas or scarring. Severe or untreated pyonephrosis can lead to complete kidney failure.

Pyonephrosis Causes

Pyonephrosis occurs when bacteria or, rarely, fungi infect the kidneys. The invaders move up to the kidney from the bladder or travel through the bloodstream from other parts of the body. Although the infection can be caused by a diverse range of different bacteria or fungi, the most frequent trigger is the bacterium Escherichia coli (E. coli). Immunocompromised patients (e.g., those with AIDS or diabetes) and those who take long-term antibiotics are at an increased risk for fungal infections.

Once the bacteria or fungi invade, the kidney's interior fills with pus, which consists of the infecting microbes, white blood cells, and dead epithelial cells from the kidney. When the abscess forms, it isolates the pus from the immune system and from antibiotics.

Upper urinary tract obstructions increase the risk of pyonephrosis. The obstruction may be caused by:

  • Kidney stones and staghorn calculi (branched mineral masses that fill the collecting funnels of the kidney)--these are the most common cause and are found in up to 75% of patients
  • Fungus infections that amass into fungal balls, which may obstruct the renal pelvis or the ureter
  • Renal tumors, testicular cancer, colon cancer, or other malignancies
  • Pregnancy
  • Congenital blockages in the urinary tract (e.g., vesicoureteral reflux, or VUR)
  • Blockages in the urinary tract caused by trauma
  • Underactive bladder caused by nerve damage or nerve disorders (e.g., neurogenic bladder)
  • Renal papillary necrosis
  • Tuberculosis
  • Duplex kidneys (two ureters coming from a singe kidney) with obstructive components

Symptoms of Pyonephrosis

Some people develop pyonephrosis so gradually that they may have no symptoms. When symptoms do manifest, they include the following:

Who's at risk?

Pyonephrosis risk increases with:

  • Immunosuppression due to medications such as steroids
  • Immunosuppression due to disease such as diabetes or HIV/AIDS
  • Urinary tract obstruction (e.g., stones, tumors)

Diagnosis of Pyonephrosis

If a patient has symptoms indicative of pyonephrosis, there are a multitude of tests a urologist can use to diagnose the condition. These include:

  • Ultrasound: Ultrasound uses safe, painless sound waves to create an image of the structure of internal organs. The images can show obstructions in the urinary tract, including physical abnormalities and calculi.

  • Computerized tomography (CT) scan: CT scans combine X-rays and computer technology to create 3-D images of internal organs, and--because they're more detailed than ultrasound images--can show obstructions in the urinary tract. A CT scan may or may not include the injection of a special dye, called contrast medium.

  • Urinalysis with urine culture: Because pyonephrosis is often accompanied by difficulty urinating, a catheter may be inserted into the urethra and advanced past any obstruction. Urine is collected in a sterile container and examined at a laboratory; if the urine contains white blood cells and bacteria, it indicates infection. Part of the urine sample is placed in a tube or dish with proteins, sugars and other substances that encourage any bacteria present to multiply so they can be identified and cultured with various antibiotics to determine which drug will most effectively treat the infection.

  • Blood tests:
    • Complete blood count (CBC) checks the number of red and white blood cells in the blood, the amount of hemoglobin in the blood, and the proportion of red blood cells to the total sample; infections often cause elevated numbers of white blood cells
    • Serum chemistry assesses the function of the kidneys and other organs
    • Blood cultures check for bacterial infection of the bloodstream
    • C-reactive protein (CRP), which is made by the liver, is usually undetectable in the blood, but levels increase when inflammation is present; the test has been shown to be useful in diagnosing pyonephrosis

If a specific cause of the obstruction cannot be found, additional tests may be needed. These may include:

  • Antegrade pyelography (or antegrade nephrostography): Detects any blockages or obstructions in the kidney. Antegrade pyelography uses a special dye, called contrast agent, to produce detailed X-rays of the kidney and ureter. An X-ray technician locates the kidneys with an ultrasound probe or a CT scan, numbs the skin, inserts a needle directly into the kidney, and injects a dye that makes the interior of the kidney visible on X-rays and so as to detect any blockages or obstructions.

  • Multichannel cystometry (or multichannel urodynamics): Checks for possible neurogenic bladder. Cystometry gauges the pressure inside of the bladder using two pressure catheters. One fills the bladder with warm water while another is placed in the vagina (female) or rectum (male) to measure the rigidity of the bladder muscle and assess its ability to hold in and push out fluid. The patient also may be asked to urinate so that urination pressure can be measured.

  • Voiding cystourethography (VCUG): Eliminates vesicoureteral reflux (VUR), or the back up of urine into the ureters or kidneys, as a potential cause of the obstruction. VCUG takes an X-ray image of the bladder and urethra while the bladder is full and as the patient urinates. This test can show abnormalities of the inside of the urethra and bladder.

Pyonephrosis Treatment

Pyonephrosis treatment starts intravenous antibiotics, but may also involve surgery to drain the puss and--depending on the seriousness of the condition--potential removal of part or all of the kidney.


Mohamed, A., and Mohamed, R. (2012). Management of Pyonephrosis: Our Experience. WebmedCentral UROLOGY. 3(5): WMC003420.

Yoder, I.C., Pfister, R.C., Lindfors, K.K., and Newhouse, J.H. (1983). Pyonephrosis: imaging and intervention. AJR: American Journal of Roentgenology. 141:735-40.

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