Renal abscess

Renal abscess, like any other abscess, is a collection of infective fluid in the kidney. It is usually a sequela of acute pyelonephritis, where severe vasospasm and inflammation may occasionally result in liquefactive necrosis and abscess formation.

Epidemiology

It can affect all ages and has no recognised gender predilection.

Clinical presentation

The most common signs or symptoms are : 

  • fever
  • flank/abdominal pain
  • chills 
  • dysuria

Radiographic features

Ultrasound

Typically, a renal abscess appears as a well-defined hypoechoic area within the cortex or in the corticomedullary parenchyma. It demonstrates internal echoes within and an associated diffusely hypoechoic kidney due to acute pyelonephritis may be seen. Perinephric collection may also be seen.

CT

CT is currently the most accurate modality for diagnosis and follow-up of renal abscesses1.  An abscess appears as a well-defined mass of low attenuation with a thick, irregular wall or pseudo capsule, which can be better visualised on contrast enhanced scans. Gas within a low attenuation/cystic mass strongly suggests abscess formation. Renal parenchyma around the abscess cavity may appear hypoenhancing in nephrogram phase, and may appear hyperattenuating in delayed images. Associated fascial and septal thickening is seen with obliteration of perinephric fat.

In some cases, the formation of a discrete abscess is preceded by acute focal lobar nephronia which is a focal inflammation of the kidney without liquefaction. It appears as a solid mass. 

Treatment and prognosis

Treatment consists of intravenous antibiotics and drainage, which may be performed under either ultrasound or CT guidance.

Complications

The main complication is abscess rupture. When it does into the calyceal system then it's called pyonephrosis, to the perinephric space (perinephric abscess), beyond Gerota fascia (paranephric abscess) and into the peritoneum (subdiaphragmatic/pelivc abscess). These complications may lead to renal atrophy secondary to compression or obstruction.

Differential diagnosis

General imaging differential considerations include:

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Article Information

rID: 6220
System: Urogenital
Synonyms or Alternate Spellings:
  • Renal abscesses
  • Abscess involving kidney
  • Kidney abscess
  • Intrarenal abscess
  • Intranephric abscess
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    Case 1
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    Renal abscess
    Case 2: on ultrasound
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    Case 2: with renal vein thrombosis
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    Case 5: complicated by psoas abscess
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