Acute pyelonephritis
- Lesion
Bacteria climbing from the bladder infect the renal pelvis and interstitium, forming abscesses and pus in the tubules.
What it is
Acute pyelonephritis is suppurative infection of the kidney's pelvis, tubules and interstitium. Almost always it ascends from the bladder, carried by gut gram-negative rods, most often Escherichia coli, helped by short female urethras, catheters, obstruction and vesicoureteral reflux. Less often, bacteria arrive in the blood (septicemia, endocarditis). Diabetes, obstruction and sickle cell disease favour the severe complications.
Structure
- Patchy, wedge-shaped yellow abscesses on the surface and cut face; one or both kidneys.
- Neutrophils fill tubules and interstitium; tubules are destroyed and abscesses coalesce.
- Papillary necrosis: grey-white to yellow necrotic papillary tips, sharply demarcated, with coagulative necrosis.
- Pyonephrosis: pus trapped above an obstruction fills the pelvis and calyces.
- Healing leaves scars that pull in the surface and flatten the calyx below them.
Step by step
- Gut bacteria colonize the periurethral area and distal urethra.
- Adhesins (P fimbriae) help them stick to urothelium and climb into the bladder.
- Catheters, urinary stasis and incomplete emptying let them multiply.
- Vesicoureteral reflux pushes infected urine up the ureter to the pelvis.
- Intrarenal reflux through open papillary ducts carries bacteria into the parenchyma, mostly at the poles.
- Neutrophils flood tubules and interstitium, forming abscesses and white cell casts.
Clinical notes
- Sudden fever, flank pain and costovertebral tenderness, with dysuria and frequency from the coexisting cystitis.
- Papillary necrosis presents with hematuria, colic or pieces of papilla in the urine; common in diabetes, sickle cell disease and analgesic abuse.
- Recurrent infections on top of reflux or obstruction lead to chronic pyelonephritis.
In the lab
- Urine with pyuria, bacteriuria and white cell casts; culture identifies the organism.
Test yourself
Think of the answer, then tap the question to see it.
What urine finding places a urinary infection in the kidney?
White blood cell casts, which form in the renal tubules.
What is the most common route of infection in acute pyelonephritis?
Ascending infection from the lower urinary tract, helped by vesicoureteral reflux.
Which three conditions predispose to papillary necrosis in pyelonephritis?
Diabetes mellitus, urinary obstruction and sickle cell disease (analgesic abuse also).
Elsewhere in DurgiPedia
Connections
Microorganisms3
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Acute Pyelonephritis (StatPearls (NCBI Bookshelf), 2024); Renal papillary necrosis: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2025).
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Representative model, for educational purposes only.