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acute pyelonephritis


  • acute pyelonephritis is a bacterial infection of the renal parenchyma
  • it usually arises from ascending bacteria in the urinary tract associated with urinary tract infections (UTIs) / cystitis
  • it is 5x more likely in females as males aged under 65 years
  • females have peak incidences at ages 0-4yrs, 15-35 years, then a gradual rise from age 50, peaking at 80yrs age.
  • males have a peak at age 0-4 years, then gradual rise from age 35yrs to a peak at 85yrs age
  • paediatric cases are often associated with underlying urologic tract abnormalities including vesicoureteral reflux
  • it develops in 20-30% of pregnant women with untreated asymptomatic bacteriuria, most often during the late second and early third trimesters
  • timely Rx is important to reduce renal damage, complications and also potentially lethal urosepsis

clinical features

  • most adult patients present with:
    • flank pain and tenderness, often with suprapubic discomfort of cystitis, developing over hours to days
    • high fever
    • anorexia, nausea +/- vomiting
  • some will be afebrile
  • some will have dysuria and frequency
  • some will have frank haematuria associated with haemorrhagic cystitis
  • elderly patients are more likely to present with delirium
  • pain radiating to the groin or testis suggests renal colic
  • children aged under 2yrs usually present with failure to thrive, feeding difficulty, fever, and vomiting
  • standard renal USS only has a 25-32% sensitivity for pyelonephritis (a contrast-enhanced US or CEUS is said to have over 85% sensitivity) but it is better than CT at differentiating pyonephrosis from hydronephrosis
  • contrast CT abdo has sens over 85% and spec of around 88% 1)
  • for patients where CT is C/I, MRI has a sens of around 90%

Mx in ED of adult patients

  • most require initial parenteral antibiotics for 12-48hrs, although some will be able to be managed as an outpatient with a single dose of parenteral antibiotic then a course of oral antibiotics
  • iv access
  • bloods for FBE, U&E
  • MSU m/c/s and urinalysis
  • look for and Rx evidence of sepsis / septicaemia as septic shock from urosepsis has a high mortality
  • consider admission into ED observation ward if uncomplicated
  • iv ceftriaxone 1g daily is a reasonable choice for most patients
  • many doctors are now steering away from the use of single dose of iv gentamicin 4-5mg/kg given recent reports of permanent ototoxicity may occur with only 1 dose (although this is a rare complication)
  • if highly likely to have resistant organisms (eg. ESBL) such as, PH ESBL, recent hospital admission or travel overseas (especial SE Asia where ESBL carriage is > 50%) and in septic shock:
    • IV meropenem (preferred over Tazocin in ESBL severe sepsis)2) + IV amikacin (to cover carbapenem resistance), consider adding IV vancomycin if Gram +ve sepsis possible
  • patients are often discharged on oral trimethoprim or cephalexin - but this depends upon your regional antibiotic resistance profiles
  • patients who have returned from India are highly likely to have a multi-resistant organism which may require consultation with infectious diseases on selection of antibiotic until sensitivities are back.
  • pregnant patients require inpatient care and prolonged course of antibiotics as they have ureteric stasis secondary to progesterone, etc, and have a higher risk of Rx failure
  • urgent urology consult if either:
    • obstructed kidney (eg. ureteric calculus) with UTI
      • patients with renal colic and infection should be referred to urology ASAP for possible intervention to drain the urine proximal to ureteric calculus causing the obstruction
    • renal abscess
    • post-urologic procedure

CT findings in pyelonephritis

  • CT is generally only indicated in pyelonephritis if either:
    • there is a persistence of fever or leukocytosis after 72 hours,
    • the diagnosis is not evident from Hx,exam,urinalysis and lab results and the patient is septic and there is a need to exclude other abdominal sources of sepsis
    • there is an associated obstructing stone which is an indication for emergent nephrostomy
  • non-contrast CT KUB:
    • may show gas, calculi, haemorrhage, renal enlargement, inflammatory masses, and obstruction
  • contrast CT abdo:
    • may show:
      • interstitial nephritis
      • early and late stages of acute pyelonephritis
        • most characteristic finding includes one or more focal/ill-defined wedge-like regions showing reduced enhancement and poor corticomedullary differentiation, corresponding to poorly or nonfunctioning parenchyma
        • global renal swelling (88%)
        • perirenal fascial thickening (76%)
        • perinephric fat stranding (56%)
        • striated nephrogram (44%)
        • abscess (44%)
        • microabscess (32%)
        • gas in renal collecting system or parenchyma suggestive of emphysematous pyelonephritis (16%)
        • abdominal wall involvement (8%)
      • complications such as abscesses and emphysematous pyelonephritis
      • xanthogranulomatous pyelonephritis (XPN)
        • XPN is a severe form of APN that occurs mostly in middle aged women in the presence of chronic obstruction and suppuration - 80% occur in association with a staghorn calculus


  • renal abscesses and perinephric abscesses which may require early surgical drainage by urology
  • renal papillary necrosis
  • xanthogranulomatous pyelonephritis
    • a rare (1% of all renal infections), serious, chronic inflammatory disorder of the kidney characterised by a destructive mass that invades the renal parenchyma
    • often associated with urinary tract obstruction, infection, urolithiasis, diabetes mellitus, and/or immunocompromise
    • 4 x more common in women than in men
    • usually occurs in the fifth and sixth decades of life but may also occur in children under 8yrs when it is more common in boys 3)
  • chronic pyelonephritis - usually children aged under 2yrs, associated with vesicoureteral reflux
  • recurrent pyelonephritis
pyelonephritis.txt · Last modified: 2024/04/08 12:50 by gary1

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