An abscess is a pocket of pus resulting from an infection. A perirenal abscess is an infection surrounding one or both kidneys.

More than 75% of perirenal abscesses are caused by urinary tract infections that start in the bladder, spread to the kidney, and then spread to the area surrounding the kidney. Other causes of perirenal abscess include urological surgery (in the urinary tract or reproductive system) and bloodstream infection.

The most significant risk factor for perirenal abscess is the presence of kidney stones that block urinary flow and serve as a reservoir for infection. Bacteria tend to stick to the stones and antibiotics can't kill the bacteria there.

Stones are found in 20-60% of patients with perirenal abscess. Other risk factors for perirenal abscess include having an abnormal urinary tract, trauma, and diabetes.

Symptoms of perirenal abscess include flank (side of the abdomen) or abdominal pain, which may extend to the groin or even down the leg. More than half of all patients have fever. Many also suffer from sweats and chills.

Signs of perirenal abscess include tenderness in the back or abdomen. A urinalysis will show white blood cells and may also find red blood cells. A urine culture, if taken before antibiotics are given, may show one or more types of bacteria. Even if the urine culture is negative, white blood cells in the urine and a fever may indicate the presence of a perirenal abscess.

A CT scan or ultrasound of the abdomen may show an inflamed kidney area, which would suggest a perirenal abscess.

Treatment of a perirenal abscess includes drainage of the pus, either by a catheter placed through the skin or via surgery. Antibiotics should also be given, initially through a vein (IV).

In general, prompt diagnosis and treatment of perirenal abscess should lead to a good outcome. If present, kidney stones must be treated to avoid further infections.

In rare cases, infection can spread beyond the kidney area and into the bloodstream, which can be deadly.

A possible complication is a continuing infection, if kidney stones are present.

Call your health care provider if you have a history of kidney stones and develop a fever, chills, burning with urination, or abdominal pain. Also call if you develop a urinary tract infection.

If you have kidney stones, ask your doctor about the best way to treat them to avoid a perirenal abscess. If you undergo urologic surgery, keep the surgical area as clean as possible.