Pyelonephritis (from Greek πήληξ – pyelum, meaning "renal pelvis", νεφρός – nephros, meaning "kidney", and -itis, meaning "inflammation") is an ascending urinary tract infection that has reached the pyelum or pelvis of the kidney. It is a form of nephritis that is also referred to as pyelitis. Severe cases of pyelonephritis can lead to pyonephrosis (pus accumulation around the kidney), urosepsis (a systemic inflammatory response of the body to infection), kidney failure and even death.
Pyelonephritis presents with fever, accelerated heart rate, painful urination, abdominal pain radiating to the back, nausea, and tenderness at the costovertebral angle on the affected side. Pyelonephritis that has progressed to urosepsis may be accompanied by signs of septic shock, including rapid breathing, decreased blood pressure, violent shivering, and occasionally delirium. Pyelonephritis requires antibiotic therapy, and sometimes surgical intervention such as ureteroscopy, percutaneous nephrostomy or percutaneous nephrolithotomy, as well as treatment of any underlying causes to prevent its recurrence. Xanthogranulomatous pyelonephritis is a rare form of chronic pyelonephritis in which nephrectomy (removal of the kidney) is usually necessary for definitive treatment.