Acute Pyelonephritis: Definition and Causes
Review literature: (Fihn, 2003) (Nickel, 2001) (Roberts, 1999) (DGU S3-Guideline urinary tract infections).
Definition of Acute Pyelonephritis
Acute pyelonephritis is a bacterial infection of the renal pelvis and the renal parenchyma with fever, flank pain and bacteriuria. Since bacterial infection of the kidney cannot be proven, acute pyelonephritis is defined clinically as a urinary tract infection with flank pain, flank tenderness and/or fever.
Etiology (Causes) of Pyelonephritis
Ascending infection is the most common cause for acute pyelonephritis. Since the female urethra is short and intestinal bacteria tend to colonize the perineum and vulva, women have significantly more often bladder infection and pyelonephritis than men. See section "General principles of urinary tract infections".
Vesicourethral reflux (VUR) leads to refluxing urine, which becomes infected. Pyelonephritis in VUR tends to causes renal scarring, since intrarenal reflux is common. The anatomy of the papillae causes an intrarenal reflux especially at the renal poles. See also section "Vesicoureteral reflux".
Renal Scarring due to Pyelonephritis:
Recurrent relapses of acute pyelonephritis produce renal scarring in children. Chronic pyelonephritis and Ask-Upmark kidney may develop. New renal scarring is not common beyond the age of 5 years, but may occur until puberty.
The cause for the vulnerability of the child's kidney for renal scarring is explained with following mechanisms:
- intra-renal reflux happens with much lower vesical pressures than in adulthood
- decreased immunocompetence for bacterial infections in the first years of life
- clinical difficulties in the early diagnosis of pyelonephritis in the first years of life
Pyelonephritis in Pregnancy:
The incidence of bacteriuria in pregnancy is 4–7%, comparable to the rate of bacteriuria without pregnancy. Of these patients with bacteriuria, approximately 20–30% develop acute pyelonephritis (1–4% of all pregnant women). The most common manifestation of pyelonephritis is the second trimester.
Complications of pyelonephritis during pregnancy: anemia (23%), sepsis (17%), transient renal failure (2%), pulmonary complications (7%) and premature births (rare). See section urinary tract infections in pregnancy.
Emphysematous pyelonephritis is a serious complication of acute pyelonephritis with high mortality (43%). Risk factors for emphysematous pyelonephritis are diabetes mellitus or upper urinary tract obstruction. Most probably, E. coli causes gas formation by fermentation. The gas remains restricted within Gerota's fascia.
Emphysematous pyelonephritis must be distinguished from a renal abscess, which also may contain gas. Renal abscess has a favorable prognosis after drainage and antibiotic treatment.
Common Pathogens of Acute Pyeloneprhitis
E. coli, Klebsiella, Enterobacter, Serratia, Pseudomonas, Proteus mirabilis and other gram-negative coliform bacteria in 80%.
Staphylococcus aureus, Staph. saprophyticus, Enterococci.
Pathology of Pyelonephritis
- Enlarged kidney with inflammatory edema
- Small subcapsular abscesses with hemorrhagic rim
- Pus-filled tubules
- The urothelium of the renal pelvis is thick and covered with exudate
Histology of Acute Pyelonephritis
Microscopy shows a dense granulocytic inflammation and tissue destruction with liquefaction in the renal parenchyma and renal pelvis. The inflammation affects especially the tubules, the glomeruli are less affected.
Index: 1–9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
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- DGU S-3 Guideline Urinary tract infections
- Epidemiologie, Diagnostik, Therapie und Management unkomplizierter bakterieller ambulant erworbener Harnwegsinfektionen bei erwachsenen Patienten
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