Renal abscess, like any other abscess, is a collection of infective fluid in the kidney. It is usually a sequelae of acute pyelonephritis, where severe vasospasm and inflammation may occasionally result in liquefactive necrosis and abscess formation.
It can affect all ages and has no recognised gender predilection.
The most common signs or symptoms are :
- flank/abdominal pain
Typically, a renal abscess appears as a well defined hypoechoic area within the cortex or in 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 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 pseudocapsule, 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 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.
The main complication is abscess rupture. When it does into calyceal system then it's called pyonephrosis, to the perinephric space (perinephric abscess), beyond Gerota fascia (paranephric abscess) and into peritoneum (subdiaphragmatic/pelivc abscess). These complications may lead to renal atrophy secondary to compression or obstruction.
Treatment and prognosis
Treatment consists of intravenous antibiotics and drainage, which may be performed under either ultrasound or CT guidance.
General imaging differential considerations include
- 1. Kawashima A, Sandler CM, Goldman SM et-al. CT of renal inflammatory disease. Radiographics. 17 (4): 851-66. Radiographics (abstract) - Pubmed citation
- 2. Papanicolaou N, Pfister RC. Acute renal infections. Radiol. Clin. North Am. 1996;34 (5): 965-95. - Pubmed citation
- 3. Ahuja AT. Diagnostic imaging ultrasound. Amirsys Inc. (2007) ISBN:1416049177. Read it at Google Books - Find it at Amazon