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Kidney non-tumor

Tubular and interstitial diseases

Acute pyelonephritis

Reviewers: Nikhil Sangle, M.D. (see Reviewers page)
Revised: 23 December 2012, last major update August 2012
Copyright: (c) 2003-2012, PathologyOutlines.com, Inc.


● 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


● Antibiotics usually eliminate symptoms in a few days (Am Fam Physician 2011;84:519, Lancet 2012;380:484)
● Persistent bacteriuria is usually associated with obstruction, diabetes and immunocompromise

Gross description

● Focal abscesses or wedge-shaped areas of suppuration

Gross images

Acute pyelonephritis

Renal papillary necrosis

Micro 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)

Micro images

Acute pyelonephritis

Virtual slides

Acute and chronic pyelonephritis

Pseudomonas abscess

End of Kidney non-tumor > Tubular and interstitial diseases > Acute pyelonephritis

Ref Updated: 8/16/12

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