title: CT histogram analysis in pathologically proven adrenal masses.
abstract: OBJECTIVE
  The purpose of this article is to evaluate a histogram analysis method for distinguishing adrenal adenomas from metastases, pheochromocytomas, and adrenocortical carcinomas on CT.
  
  
  METHODS
  A pathology database was searched, and 335 adrenalectomies from 1995 to 2002 were identified. CT images were available for retrospective review in 187 patients (93 males, 94 females; age range, 15-84 years; mean age, 55.2 years) with 208 adrenal masses. This included 112 adenomas in 104 patients, 48 metastases in 39 patients, 40 pheochromocytomas in 36 patients, and eight adrenocortical carcinomas in eight patients. Histogram analysis was performed using a circular region of interest for mean attenuation, number of pixels, number of negative pixels (< 0 H), and percentage of negative pixels by two interpreters. Areas of necrosis were excluded from measurements. Observer agreement was calculated.
  
  
  RESULTS
  In 72 of 76 (94.7%) and 63 of 72 (87.5%) adenomas, respectively, interpreters found attenuation values greater than 10 H contained negative pixels on unenhanced CT scans. None of the enhanced adenomas had mean attenuation less than or equal to 10 H, but 24 (38.7%) and 28 (45.2%), respectively, had negative pixels. Negative pixels were present in unenhanced and enhanced metastases, pheochromocytomas, and carcinomas. Using a 5% or 10% negative pixel threshold value to diagnose adenoma improved specificity but diminished sensitivity. Specificity for a 10% negative pixel threshold was approximately 88% for unenhanced CT scans and 99% for enhanced CT scans, with sensitivities of 71% and 12%, respectively.
  
  
  CONCLUSIONS
  Although specificity for the diagnosis of adenomas on enhanced CT scans with histogram analysis was high when a 10% negative pixel threshold was used, low sensitivity likely limits clinical usefulness.
authors.affiliation: Division of Radiology, Cleveland Clinic Foundation, 9500 Euclid Avenue, Desk A21, Cleveland, Ohio 44195, USA. remere1@ccf.org
authors.forename: Erick M
authors.initials: EM
authors.lastname: Remer
authors.forename: Gaspar A
authors.initials: GA
authors.lastname: Motta-Ramirez
authors.forename: Laura B
authors.initials: LB
authors.lastname: Shepardson
authors.forename: Amir H
authors.initials: AH
authors.lastname: Hamrahian
authors.forename: Brian R
authors.initials: BR
authors.lastname: Herts
mesh_terms: D000236:Adenoma / Q000000981:diagnostic imaging; D000293:Adolescent; D000310:Adrenal Gland Neoplasms / Q000000981:diagnostic imaging*; D018268:Adrenocortical Carcinoma / Q000000981:diagnostic imaging; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003287:Contrast Media; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008875:Middle Aged; D010673:Pheochromocytoma / Q000000981:diagnostic imaging; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed
chemical_list: D003287:Contrast Media