Kidney nontumor
Acute pyelonephritis

Topic Completed: 27 November 2018

Minor changes: 10 October 2020

Copyright: 2003-2020,, Inc.

PubMed Search: Acute pyelonephritis [title]

Nikhil Sangle, M.D.
Page views in 2019: 5,677
Page views in 2020 to date: 5,567
Cite this page: Sangle N. Acute pyelonephritis. website. Accessed November 23rd, 2020.
Definition / general
  • Acute suppurative (pus forming) infection of kidney collecting system as well as renal parenchyma
  • Affects infants and young children with congenital lesions, women of childbearing age, men and women age 60+ years (due to nodular hyperplasia of prostate, cystoceles in women, cervical carcinoma, nephrolithiasis)
  • Also associated with diabetes or immunocompromise
Clinical features
  • Causes: urinary tract infection (UTI), instrumentation, obstruction, pregnancy (4 - 6% have bacteriuria, 20% have symptoms if untreated), vesicoureteral reflux
  • Bacterial UTI: due to colonization of distal urethra and introitus by coliform bacteria with adhesins on P-fimbriae (pili), plus upward spread via instrumentation or catheterization; more common in women than men due to short urethra, no anti-bacterial prostatic fluid, hormonal changes, sex-related trauma
  • Usually gram negative rods from fecal flora (E. coli, Enterobacter, Klebsiella, Proteus, Streptococcus faecalis) or Staph
  • Ascending route most common; also hematogenous spread of bacteria to kidney
  • Intrarenal reflux: via open ducts at tips of papillae; most common at poles of kidney where papillae have flat or concave tips; demonstrate via voiding cystourethrogram (seen in 50% of children with UTI)
  • Vesicoureteral reflux:due to short intravesical ureter, spinal cord injuries; some UTIs; independent risk factor for renal scar formation after acute pyelonephritis in infants (J Urol 2012;187:1032)
  • Signs / symptoms: sudden onset of costovertebral angle pain, symptoms of systemic infection or urinary tract infection, pyuria or white blood cell casts
  • Papillary necrosis: more common with diabetes and urinary tract obstruction; usually bilateral; variable number of pyramids involved; coagulative necrosis of tubules; usually limited white blood cell response
  • Perinephric abscess: extension of pus through renal capsule into adjacent tissue
  • Pyonephrosis: total or almost complete obstruction prevents drainage of pus
Gross description
  • Focal abscesses or wedge-shaped areas of suppuration
Gross images

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Acute pyelonephritis

Microscopic (histologic) description
  • Patchy suppurative inflammation, primarily cortical, with edema, neutrophils in interstitium and tubular lumina, and tubular necrosis
  • Cortical abscesses and necrosis
  • Glomeruli and vessels usually normal (Candida affects glomeruli)
Microscopic (histologic) images

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Acute pyelonephritis

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