title: Segmental enhancement inversion at biphasic multidetector CT: characteristic finding of small renal oncocytoma.
abstract: OBJECTIVE
  To retrospectively determine the usefulness of segmental enhancement inversion during the corticomedullary phase (CMP) and early excretory phase (EEP) of biphasic multidetector computed tomography (CT) in differentiating small renal oncocytoma from renal cell carcinoma (RCC).
  
  
  METHODS
  This retrospective study was institutional review board approved; informed consent was waived. Between January 2004 and December 2006, 98 patients with pathologically confirmed renal masses smaller than 4 cm (10 renal oncocytomas and 88 RCCs) were included in this study. Segmental enhancement inversion was defined as follows: In a mass with two segments showing different degrees of enhancement during CMP, the relatively highly enhanced segment became less enhanced during EEP, whereas the less-enhanced segment during CMP became highly enhanced during EEP. Two experienced radiologists retrospectively assessed the presence of segmental inversion in all masses and measured attenuation with consensus. The Fisher exact test was used to determine the significance of segmental enhancement inversion in differentiating small renal oncocytoma from RCC.
  
  
  RESULTS
  Eight of 10 renal oncocytomas and only one of 88 RCCs showed segmental inversion during CMP and EEP, which significantly differentiated small renal oncocytomas and RCCs (P < .0001). For differentiating oncocytoma from RCC, segmental inversion was found to have a sensitivity of 80% (eight of 10), a specificity of 99% (87 of 88), a positive predictive value of 89% (eight of nine), and a negative predictive value of 98% (87 of 89). The mean values of the attenuation differences shown by two segments during CMP and EEP were 62.75 HU +/- 36.96 (standard deviation) and -36.88 HU +/- 20.02, respectively.
  
  
  CONCLUSIONS
  Segmental enhancement inversion during CMP and EEP was found to be a characteristic enhancement pattern of small renal oncocytoma at biphasic multidetector CT and it may help in differentiating small oncocytoma from RCC.
  
  
  BACKGROUND
  http://radiology.rsnajnls.org/cgi/content/full/2522081180/DC1.
authors.affiliation: Department of Radiology, Institute of Radiation Medicine, Seoul National University Hospital, 28 Yongon-dong, Chongno-gu, Seoul 110-744, Korea.
authors.forename: Jung Im
authors.initials: JI
authors.lastname: Kim
authors.forename: Jeong Yeon
authors.initials: JY
authors.lastname: Cho
authors.forename: Kyung Chul
authors.initials: KC
authors.lastname: Moon
authors.forename: Hak Jong
authors.initials: HJ
authors.lastname: Lee
authors.forename: Seung Hyup
authors.initials: SH
authors.lastname: Kim
mesh_terms: D018249:Adenoma, Oxyphilic / Q000000981:diagnostic imaging*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002292:Carcinoma, Renal Cell / Q000000981:diagnostic imaging*; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D007680:Kidney Neoplasms / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D011856:Radiographic Image Enhancement / Q000379:methods*; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods*; D055815:Young Adult