title: Adrenal nonhyperfunctioning adenoma and nonadenoma: CT attenuation value as discriminative index.
abstract: BACKGROUND
  When an asymptomatic adrenal mass is incidentally discovered on abdominal CT scans, the distinction between a nonhyperfunctioning adenoma and a nonadenoma would be important.
  
  
  METHODS
  We evaluated the CT findings of 36 adrenal masses (14 nonhyperfunctioning adenomas, 22 nonadenomas) in 34 patients with no evidence of hormonal hypersecretion. CT attenuation values of adrenal masses on CT scans were calculated by setting a circular region of interest as large as possible in the center of each adrenal mass.
  
  
  RESULTS
  Below 20 HU in CT attenuation values, all adrenal masses, except one case of ganglioneuroma with myxomatous change, were nonhyperfunctioning adenomas. With an arbitrary threshold of 20 HU, the sensitivity of CT attenuation values in distinguishing nonhyperfunctioning adenomas from nonadenomas was 64%, the specificity was 95%, and the accuracy was 83%. When decreasing the threshold to 15 HU, the sensitivity was 64%, the specificity was 100%, and the accuracy was 86%. The CT attenuation value on noncontrast CT was more useful for making this distinction than the size and interior homogeneity.
  
  
  CONCLUSIONS
  Our data suggest that an asymptomatic adrenal mass with homogeneous low attenuation (< or = 15 HU) and less than or equal to 4 cm indicates a nonhyperfunctioning adenoma, and no further examinations are necessary. CT attenuation value on non-contrast CT is the most important discriminatory factor.
authors.affiliation: Department of Radiology, Oita Medical University, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Miyake
authors.forename: H
authors.initials: H
authors.lastname: Takaki
authors.forename: S
authors.initials: S
authors.lastname: Matsumoto
authors.forename: S
authors.initials: S
authors.lastname: Yoshida
authors.forename: T
authors.initials: T
authors.lastname: Maeda
authors.forename: H
authors.initials: H
authors.lastname: Mori
mesh_terms: D000236:Adenoma / Q000000981:diagnostic imaging*; D000310:Adrenal Gland Neoplasms / Q000000981:diagnostic imaging* / Q000556:secondary; D000311:Adrenal Glands / Q000000981:diagnostic imaging; D018246:Adrenocortical Adenoma / Q000000981:diagnostic imaging*; D003937:Diagnosis, Differential; D006801:Humans; D009384:Paraneoplastic Endocrine Syndromes / Q000000981:diagnostic imaging*; D011856:Radiographic Image Enhancement; D014057:Tomography, X-Ray Computed