title: Perirenal lucency ("kidney sweat"): a new sign of renal failure.
abstract: OBJECTIVE
  This study describes a new sonographic finding in renal failure: perirenal lucency, which we call the "kidney sweat" sign.
  
  
  METHODS
  During 1 year at our institution, 502 renal sonograms were obtained. Sonography evaluated 330 patients with renal failure. All of the examinations were retrospectively analyzed.
  
  
  RESULTS
  An extracapsular hypoechoic rim was present in 47 (14%) of the 330 patients with renal failure. The finding, when present, was always bilateral. The hypoechoic rim was not present in the remaining 283 patients with renal failure. Forty (85%) of the 47 patients had kidneys that were hyperechoic compared with the liver. Twenty-eight (60%) of the 47 patients had kidneys that were hyperechoic compared with the spleen. In 15 (32%) of the 47 patients, the kidneys were small. Ascites was present in 11 (23%) of the 47 patients. Of the 283 patients with renal failure whose sonograms did not show the hypoechoic rim, 76 patients had normal sonographic findings. The remaining 207 patients with renal failure who did not show the kidney sweat sign had hydronephrosis, stones, cysts, echogenic kidneys, small kidneys, or ascites.
  
  
  CONCLUSIONS
  An extracapsular hypoechoic rim is found in patients with renal failure. We call this finding "kidney sweat." We believe, but cannot currently prove, that the kidney sweat sign represents edema. It is an additional sonographic finding in patients with renal failure.
authors.affiliation: Department of Radiology, USC/Norris Comprehensive Cancer Hospital and Research Center, Los Angeles, CA 90033, USA.
authors.forename: N A
authors.initials: NA
authors.lastname: Yassa
authors.forename: M
authors.initials: M
authors.lastname: Peng
authors.forename: P W
authors.initials: PW
authors.lastname: Ralls
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D007668:Kidney / Q000000981:diagnostic imaging; D008297:Male; D008875:Middle Aged; D051437:Renal Insufficiency / Q000000981:diagnostic imaging*; D012189:Retrospective Studies; D014463:Ultrasonography