Fact-sheet: Acute focal pyelonephritis


Updated on 04/19/2018 at 4:40 PM

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Definition

Severe form of acute pyelonephritis

  • Non-liquefied infectious lesion (usually solitary)
  • Lobar topography
  • Ascending urinary tract infection ++ > hematogenous
  • Gram-negative bacilli ++: E coli
  • Population at risk:
  • Young women
  • Diabetic patients

Note: differs from an abscess, which is liquefied → drainage

Clinical features

Clinical presentation corresponds to that of severe pyelonephritis:

  • Flank pain refractory to treatment
  • Nausea and vomiting
  • Marked dysuria +/- pyuria
  • High fever 39–40 °C
  • Chills
  • Marked deterioration of general condition

Laboratory findings

  • Marked neutrophilic leukocytosis (15 to 20 G)
  • Abnormal urine dipstick ++: RBC / WBC / nitrites
  • Blood cultures mandatory!

Ultrasound

  • Kidney of preserved size (unlike simple pyelonephritis, in which it is generally rounded and enlarged)
  • Roughly rounded, hypoechoic intraparenchymal lesion.
  • A normal ultrasound does not exclude the diagnosis!
  • Contrast-enhanced ultrasound is useful, being more sensitive for detecting a hypovascular focal nephritis lesion

CT

  • Normal-sized kidney
  • Roughly rounded hypodense focus
  • Partial lack of enhancement of the lesion following contrast injection
  • Possible mass effect on the parenchyma (unlike the triangular foci seen in focal nephritis)
  • Infiltration of the perirenal fat and fascia (Gerota's fascia)

Management

Urine culture followed by appropriate antibiotic therapy; if progression to a liquefied abscess occurs --> drainage.

Differential diagnosis

  • Renal infarctus: arguing against this hypothesis is the even partial lesional enhancement, the possible mass effect, and the absence of enhancement of the cortex corticis.
  • Renal abscess: collected, unlike acute focal nephritis
  • Renal tumor (notably hypovascular papillary adenocarcinoma) and renal metastases.