title: Renal cell carcinoma attenuation values on unenhanced CT: importance of multiple, small region-of-interest measurements.
abstract: Since it has been suggested that benign renal cysts can be diagnosed at unenhanced CT on the basis of homogeneity and attenuations of 20 HU or less, we determined the prevalence of renal cell carcinomas (RCCs) with these characteristics using two different methods of measuring attenuation.
  
  
  
  After IRB approval, two radiologists obtained unenhanced attenuation values of 104 RCCs (mean size 5.6 cm) using a single, large region of interest (ROI), two-thirds the size of the mass. They were then determined if the masses appeared heterogeneous. Of RCCs measuring 20 HU or less, those which appeared homogeneous were re-measured with multiple (6 or more), small (0.6 cm2or smaller) ROIs dispersed throughout the lesion. Masses with attenuations 20 HU or less were compared to those with masses with HU greater than 20 for any differences in demographic data.
  
  
  
  Of 104 RCCS, 24 RCC had HU less than 20 using a large ROI. Of these, 21 appeared heterogeneous and 3 appeared homogeneous. Using multiple small ROIs, these three RCCs revealed maximum attenuation values above 20 HU (Range: 26-32 HU). A greater portion of RCCs measuring 20 HU or less using a large ROI were clear cell sub-type. There were no other differences.
  
  
  
  Renal cell carcinoma can measure 20 HU or less at unenhanced CT when a single large ROI is used. While most appear heterogeneous, some may appear homogeneous, but will likely reveal attenuations greater than 20 HU when multiple, small ROIs are used. This knowledge may prevent some RCCs from being misdiagnosed as cysts on unenhanced CT.
authors.affiliation: Department of Radiology, Davis Medical Center, University of California, 4860 Y St, Suite 3100, Sacramento, CA, 95817, USA. jpmcgahan@ucdavis.edu.
authors.forename: John P
authors.initials: JP
authors.lastname: McGahan
authors.affiliation: Department of Radiology, Davis Medical Center, University of California, 4860 Y St, Suite 3100, Sacramento, CA, 95817, USA.
authors.forename: Kunal
authors.initials: K
authors.lastname: Sidhar
authors.affiliation: Department of Radiology, Davis Medical Center, University of California, 4860 Y St, Suite 3100, Sacramento, CA, 95817, USA.
authors.forename: Ghaneh
authors.initials: G
authors.lastname: Fananapazir
authors.affiliation: Department of Radiology, Davis Medical Center, University of California, 4860 Y St, Suite 3100, Sacramento, CA, 95817, USA.
authors.forename: Heather
authors.initials: H
authors.lastname: Early
authors.affiliation: Department of Radiology, Davis Medical Center, University of California, 4860 Y St, Suite 3100, Sacramento, CA, 95817, USA.
authors.forename: Michael T
authors.initials: MT
authors.lastname: Corwin
authors.affiliation: Department of Radiology, Brigham and Women's Hospital, 75 Francis St, Boston, MA, 02115, USA.
authors.forename: Stuart G
authors.initials: SG
authors.lastname: Silverman
authors.affiliation: Department of Radiology, Davis Medical Center, University of California, 4860 Y St, Suite 3100, Sacramento, CA, 95817, USA.
authors.forename: Anthony
authors.initials: A
authors.lastname: Seibert
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002292:Carcinoma, Renal Cell / Q000000981:diagnostic imaging*; D003287:Contrast Media; D005260:Female; D006801:Humans; D007680:Kidney Neoplasms / Q000000981:diagnostic imaging*; 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
keywords: CT; Enhanced CT; Hounsfield units; Kidney; Renal cell carcinoma