title: Visualization of renal medullary hyperattenuation at unenhanced CT: what is the effect of furosemide administration?
abstract: OBJECTIVE
  To retrospectively investigate the effects of furosemide on the visualization of renal medullary hyperattenuation at unenhanced computed tomography (CT).
  
  
  METHODS
  This retrospective single-institution study was HIPAA compliant and approved by the institutional review board; requirement for informed consent was waived. This study identified 289 consecutive patients (152 men, 137 women; mean age, 59 years) without ureteral obstruction who underwent unenhanced scanning as part of CT urography; of these, 178 patients did not receive intravenous furosemide prior to imaging and 111 did. The presence of renal medullary hyperattenuation, renal stones, and bladder urine attenuation levels were recorded and compared between patients who did not receive furosemide prior to imaging and those who did by using the chi(2) and unpaired Student t tests. A multiple logistic regression model was used to evaluate independent predictors of visualization of renal medullary hyperattenuation.
  
  
  RESULTS
  Renal medullary hyperattenuation was seen less commonly in patients who received furosemide (27 of 111, 24%) than in those who did not receive furosemide prior to imaging (79 of 178, 44%, P = .001). Bladder urine attenuation was lower in patients who received furosemide (-0.1 HU) compared with those who did not (6.4 HU, P < .001). A multiple logistic regression model revealed independent associations between the visualization of renal medullary hyperattenuation and the absence of furosemide administration (P = .002), younger age (P < .001), and presence of renal stones (P = .047).
  
  
  CONCLUSIONS
  Furosemide administration prior to unenhanced CT is associated with decreased visualization of renal medullary hyperattenuation.
authors.affiliation: Department of Radiology, University of California San Francisco, 505 Parnassus Ave, Box 0628, C-372C, San Francisco, CA 94143-0628, USA.
authors.forename: Rahi
authors.initials: R
authors.lastname: Kumar
authors.forename: Zhen J
authors.initials: ZJ
authors.lastname: Wang
authors.forename: Yanjun
authors.initials: Y
authors.lastname: Fu
authors.forename: Carlos
authors.initials: C
authors.lastname: Forsythe
authors.forename: Emily M
authors.initials: EM
authors.lastname: Webb
authors.forename: Benjamin M
authors.initials: BM
authors.lastname: Yeh
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016009:Chi-Square Distribution; D003287:Contrast Media; D004232:Diuretics / Q000008:administration & dosage*; D005260:Female; D005665:Furosemide / Q000008:administration & dosage*; D006417:Hematuria / Q000000981:diagnostic imaging*; D006801:Humans; D007472:Iohexol; D007679:Kidney Medulla / Q000000981:diagnostic imaging*; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D011857:Radiographic Image Interpretation, Computer-Assisted; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D003287:Contrast Media; D004232:Diuretics; D007472:Iohexol; D005665:Furosemide