title: Diffusion-weighted MR imaging in thymic epithelial tumors: correlation with World Health Organization classification and clinical staging.
abstract: OBJECTIVE
  To assess thymic epithelial tumors with diffusion-weighted magnetic resonance (MR) imaging.
  
  
  METHODS
  Informed consent from patients and institutional review board approval were obtained. Prospective study was conducted on 30 consecutive patients (21 men and nine women; age range, 35-71 years) with thymic epithelial tumors. They underwent true fast imaging with steady-state precession and single-shot echo-planar diffusion-weighted MR imaging of the mediastinum with b values of 0, 400, and 800 sec/mm(2). Apparent diffusion coefficient (ADC) of the thymic epithelial tumors was calculated by the same observer at two settings and was correlated with World Health Organization classification and clinical staging.
  
  
  RESULTS
  There was significant difference in longest diameter (P = .001) and necrotic part of the tumor (P = .014) between low-risk thymoma, high-risk thymoma, and thymic carcinoma. Mean ADC value of both readings of thymic epithelial tumors (n = 30) was 1.24 × 10(-3) mm(2)/sec and 1.22 × 10(-3) mm(2)/sec, with good intraobserver agreement (κ = 0.732). There was significant difference in both readings (P = .01 and .20) of low-risk thymoma (1.30 × 10(-3) mm(2)/sec and 1.29 × 10(-3) mm(2)/sec), high-risk thymoma (1.16 × 10(-3) mm(2)/sec and 1.14 × 10(-3) mm(2)/sec), and thymic carcinoma (1.18 × 10(-3) mm(2)/sec and 1.06 × 10(-3) mm(2)/sec). Cutoff ADC values of both readings used to differentiate low-risk thymoma from high-risk thymoma and thymic carcinoma were 1.25 and 1.22 × 10(-3) mm(2)/sec with area under the curve of 0.804 and 0.851, respectively. There was significant difference in both readings of ADC value of early (stage I, II) and advanced stages (stage III, IV) of thymic epithelial tumors (P = .006 and .005, respectively).
  
  
  CONCLUSIONS
  ADC value is a noninvasive, reliable, and reproducible imaging parameter that may help to assess and characterize thymic epithelial tumors.
authors.affiliation: From the Departments of Diagnostic Radiology (A.A.K.A.R.), Chest (M.K.), and Pathology (N.N.), Mansoura Faculty of Medicine, Mansoura, Egypt 13351.
authors.forename: Ahmed Abdel Khalek
authors.initials: AA
authors.lastname: Abdel Razek
authors.forename: Mohamed
authors.initials: M
authors.lastname: Khairy
authors.forename: Nadia
authors.initials: N
authors.lastname: Nada
mesh_terms: D000328:Adult; D000368:Aged; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging; D009375:Neoplasms, Glandular and Epithelial / Q000473:pathology*; D011379:Prognosis; D011446:Prospective Studies; D013953:Thymus Neoplasms / Q000473:pathology*; D014057:Tomography, X-Ray Computed; D014944:World Health Organization