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Video: Pyelonephritis
Video: Acute pyelonephritis (urinary tract infection) - causes, symptoms & pathology 2023, February

Kidney inflammation: causes & forms

Kidney inflammation (pyelonephritis) is the most common bacterial infection of the upper urinary tract. Usually it only affects one kidney, rarely both kidneys. Mostly a previous or existing cystitis is the reason. Pathogenic bacteria enter the urinary bladder via the urethra and from there via the ureter into the interior of the kidney and collect in the renal pelvis.


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  • Forms of pelvic inflammation
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The inflammation often spreads to the surrounding kidney tissue (parenchyma). Urinary flow disorders result in the formation of residual urine, which promotes bacterial growth. The infection rarely passes from the blood to the kidneys.

Forms of pelvic inflammation

A distinction is made between uncomplicated and complicated forms. If there are severe systemic signs of inflammation, if there is pregnancy or diabetes mellitus, or if the urinary tract is obstructed, a complicated course must be expected. In acute renal pelvic inflammation there is significant pain. If not properly treated, it can develop into chronic kidney inflammation.

Pyelonephritis causative agent

The most common cause of uncomplicated renal pelvic inflammation is the intestinal bacterium Escherichia coli (E. coli for short), followed by the germ Staphylococcus saprophyticus. Complex forms show a broader spectrum of pathogens, but E. coli is usually the trigger.

Risk factors

  • Female sex: The significantly shorter urethra favors the ascent of pathogens.
  • Frequent sexual intercourse: can lead to the spread of bacteria, which sometimes ascend to the kidneys via the urethra.
  • Pregnancy: The enlarged uterus presses on the ureters and causes urine to congest. If bacteria accumulate in the upper urinary tract, pyelonephritis can develop.
  • Drainage obstruction: through narrowing or obstruction of the ureter or tube in the case of congenital anomalies such as constrictions in the renal pelvic duct, cystic kidneys and enlargement of the prostate, kidney or urinary stones.
  • Chronic illnesses: Diabetes mellitus can lead to kidney damage, for example.
  • Frequent use of painkillers: kidney damage can result.
  • Non-functioning (permanent) urinary catheters: promote bacterial growth.
  • Urination disorders: in neurological diseases such as multiple sclerosis or paraplegia.

A chronic course is favored by:

  • unresolved urinary flow disorders or urinary tract abnormalities;
  • recurring formation of urinary stones. These serve as a “nesting place” for pathogens;
  • Concomitant symptoms of diabetes mellitus such as changes in the blood vessels in the kidneys, immune deficiency and changes in the urine such as sugar (glucosuria) or acid (aciduria),
  • Kidney restrictions due to long-term use of painkillers (analgesic nephropathy).

Special form: reflux from the urinary bladder

So-called vesicorenal reflux (also: vesicoureterorenal reflux) occurs mainly in children and can lead to kidney inflammation. Due to a congenital disorder of the muscle structure between the urinary bladder and ureter, the valve closure of the ureter does not work properly.

Urine flows back from the bladder into the kidneys (reflux). This makes it easier for bacteria to penetrate the kidneys. In most cases, this malformation heals by itself as it grows.

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