title: Thymic measurements in pathologically proven normal thymus and thymic hyperplasia: intraobserver and interobserver variabilities.
abstract: OBJECTIVE
  To determine the intraobserver and interobserver variabilities of thymic measurements on computed tomography (CT) in patients with pathologic diagnosis of thymic hyperplasia or normal thymus.
  
  
  METHODS
  Thirty-three patients with pathologic diagnosis of thymic hyperplasia (n = 25) or normal thymus (n = 8) who had identifiable thymus gland on CT were retrospectively studied. Two radiologists independently measured thymic size and CT attenuation. Concordance correlation coefficients (CCCs) and Bland-Altman plots were used to assess intraobserver and interobserver agreements.
  
  
  RESULTS
  The intraobserver and interobserver agreements of thymic diameters and the lobe length were moderate, with CCCs ranging from 0.73 to 0.89 and from 0.72 to 0.81, respectively. Higher agreement was noted among patients whose measurements were performed on the same CT image in two independent measurements, with intraobserver CCC ≥ 0.95 for diameters and length. After providing readers with an instruction for consistent selection of CT image for measurements, the intraobserver and interobserver agreements improved, resulting in CCCs ranging from 0.81 to 0.92 and from 0.77 to 0.85 for diameters and length, respectively. Thymic lobe thickness had the least agreement. CT attenuation measurements were highly reproducible, with CCCs ranging from 0.88 to 0.97. In patients with thymic CT attenuation >30 HU (Hounsfield unit), the attenuation measurements were more reproducible with narrower 95% limits of agreement.
  
  
  CONCLUSIONS
  Thymic size measurements had moderate-to-high intraobserver and interobserver agreements, when the instruction for consistent selection of images was provided to the readers. CT attenuation was highly reproducible, with higher reproducibility for thymic glands with >30 HU. Awareness of thymic measurement variability is necessary when interpreting measured values of normal thymus and thymic pathology on CT.
authors.affiliation: Department of Radiology, Brigham and Women's Hospital, 75 Francis St, Boston, 02215 MA.
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Araki
authors.affiliation: Department of Pathology, Brigham and Women's Hospital, Boston, MA.
authors.forename: Lynette M
authors.initials: LM
authors.lastname: Sholl
authors.affiliation: Department of Radiology, Brigham and Women's Hospital, 75 Francis St, Boston, 02215 MA.
authors.forename: Victor H
authors.initials: VH
authors.lastname: Gerbaudo
authors.affiliation: Department of Radiology, Brigham and Women's Hospital, 75 Francis St, Boston, 02215 MA.
authors.forename: Hiroto
authors.initials: H
authors.lastname: Hatabu
authors.affiliation: Department of Radiology, Brigham and Women's Hospital, 75 Francis St, Boston, 02215 MA; Department of Imaging, Dana-Farber Cancer Institute, Harvard Medical School, 450 Brookline Ave, Boston, 02215 MA. Electronic address: Mizuki_Nishino@DFCI.HARVARD.EDU.
authors.forename: Mizuki
authors.initials: M
authors.lastname: Nishino
mesh_terms: D000328:Adult; D000368:Aged; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D015203:Reproducibility of Results; D012189:Retrospective Studies; D013950:Thymus Gland / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D013952:Thymus Hyperplasia / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed / Q000379:methods*; D055815:Young Adult
keywords: Thymus; computed tomography; interobserver variability; intraobserver variability; measurement