Pyelonephritis classification

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Usama Talib, BSc, MD [2]


Pyelonephritis is an upper urinary tract infection. Pyelonephritis may be classified according to the duration of disease and etiology into 5 subtypes: acute uncomplicated, acute complicated, chronic, emphysematous, and xanthogranulomatous pyelonephritis. Most cases of Pyelonephritis are acute uncomplicated and occur in normal healthy individuals with no history of a structural urinary tract anomaly or any long-term disease. Classification of pyelonephritis helps understand dynamics and specify treatments according to the duration, severity and the type of pyelonephritis.


There are five different types of pyelonephritis:[1][2][3][4][5][6][7]

  • Acute Uncomplicated Pyelonephritis
  • Acute pyelonephritis is a common clinical diagnosis in normally healthy patients who present with fever, chills, and flank tenderness.[8][9]
  • Infections typically result from ascending retrograde spread through the collecting ducts into the renal parenchyma.
  • Patients are referred for CT evaluation of acute pyelonephritis when symptoms are poorly localized or complications are suspected.
  • Acute Complicated Pyelonephritis
  • Acute complicated Pyelonephritis is the type that occurs in patients with known structural abnormalities of the urinary tract, pregnant or post menopausal women or in the presence of a disease like diabetes.
  • Acute complicated pyelonephritis requires a prolong duration of broad spectrum antibiotics.
  • CT scan is used for confirmation and for detection of complications.
  • Chronic Pyelonephritis
  • Chronic pyelonephritis is a somewhat controversial disease from a pathogenetic standpoint. It is unclear that, whether it is an active chronic infection, arises from multiple recurrent infections, or represents stable changes from a remote single infection.
  • Hypertension is frequently a long-term sequela and so is an iliopsoas abscess.
  • Xanthogranulomatous Pyelonephritis
  • Xanthogranulomatous pyelonephritis (XGP) is a rare inflammatory condition usually secondary to chronic obstruction caused by nephrolithiasis and resulting in infection and irreversible destruction of the renal parenchyma.
  • XGP is associated with a staghorn calculus in approximately 70% of cases.
  • Patients with diabetes are particularly predisposed to the formation of XGP.
  • Treatment is nephrectomy.
  • At histologic analysis, the inflammatory mass is composed of lipid-laden macrophages and chronic inflammatory cells.


  1. Hooton TM (2012). "Clinical practice. Uncomplicated urinary tract infection". N Engl J Med. 366 (11): 1028–37. doi:10.1056/NEJMcp1104429. PMID 22417256.
  2. Lucaj R, Achong DM (2017). "Concurrent Diffuse Pyelonephritis and Prostatitis: Discordant Findings on Sequential FDG PET/CT and 67Ga SPECT/CT Imaging". Clin Nucl Med. 42 (1): 73–75. doi:10.1097/RLU.0000000000001415. PMID 27824318.
  3. Kawamoto A, Sato R, Takahashi K, Luthe SK (2016). "Iliopsoas abscess caused by chronic urolithiasis and pyelonephritis". BMJ Case Rep. 2016. doi:10.1136/bcr-2016-218541. PMID 27974344.
  4. Peng CZ, How CK (2017). "Diagnostic Challenge of Emphysematous Pyelonephritis". Am J Med Sci. 353 (1): 93. doi:10.1016/j.amjms.2016.03.002. PMID 28104111.
  5. Wang HD, Zhu XF, Xu X, Li GZ, Liu N, He F; et al. (2017). "Emphysematous Pyelonephritis Treated with Vacuum Sealing Drainage". Chin Med J (Engl). 130 (2): 247–248. doi:10.4103/0366-6999.198021. PMID 28091422.
  6. Upasani A, Barnacle A, Roebuck D, Cherian A (2016). "Combination of Surgical Drainage and Renal Artery Embolization: An Alternative Treatment for Xanthogranulomatous Pyelonephritis". Cardiovasc Intervent Radiol. doi:10.1007/s00270-016-1522-z. PMID 28028578.
  7. Yeow Y, Chong YL (2016). "Xanthogranulomatous pyelonephritis presenting as Proteus preperitoneal abscess". J Surg Case Rep. 2016 (12). doi:10.1093/jscr/rjw211. PMC 5159021. PMID 27915241.
  8. Kasper, Dennis (2015). Harrison's principles of internal medicine. New York: McGraw Hill Education. ISBN 978-0071802154.
  9. Echols RM, Tosiello RL, Haverstock DC, Tice AD (1999). "Demographic, clinical, and treatment parameters influencing the outcome of acute cystitis". Clin Infect Dis. 29 (1): 113–9. doi:10.1086/520138. PMID 10433573.

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