title: 18F-FDG PET/CT of thymic epithelial tumors: usefulness for distinguishing and staging tumor subgroups.
abstract: The purpose of our study was to assess the usefulness of integrated PET/CT using 18F-FDG for distinguishing thymic epithelial tumors according to the World Health Organization (WHO) classification.
  
  
  METHODS
  Thirty-three patients (age range, 34-68 y; mean age, 54.6 y) with thymic epithelial tumors, who underwent both integrated PET/CT and enhanced CT, were included. The clinicopathologic stages, maximum standardized uptake values (SUVs), and uptake patterns of tumors on integrated PET/CT images, and various enhanced CT findings, are described according to the simplified (low-risk [types A, AB, and B1] and high-risk [types B2 and B3] thymomas and thymic carcinomas) subgroups of the WHO classification. Discriminant analysis was performed to determine the relative capabilities of integrated PET/CT and enhanced CT findings to differentiate tumor subgroups.
  
  
  RESULTS
  Tumors included 8 low-risk thymomas, 9 high-risk thymomas, and 16 thymic carcinomas. The maximum SUVs of high-risk thymomas (P < 0.001) and low-risk thymomas (P < 0.001) were found to be significantly lower than those of thymic carcinomas. Homogeneous 18F-FDG uptake within tumors was more frequently seen in thymic carcinomas than in high-risk thymomas (P = 0.027) or low-risk thymomas (P = 0.001). The uptake pattern (homogeneous vs. heterogeneous) on integrated PET/CT images and the presence of mediastinal fat invasion on enhanced CT images were found to be useful for differentiating tumor subgroups. In addition, integrated PET/CT helped detect lymph node metastases, which were not identified on enhanced CT in 2 patients.
  
  
  CONCLUSIONS
  Integrated PET/CT was found to be useful for differentiating subgroups of thymic epithelial tumors and for staging the extent of the disease.
authors.affiliation: Department of Radiology and Center for Imaging Science, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
authors.forename: Yon Mi
authors.initials: YM
authors.lastname: Sung
authors.forename: Kyung Soo
authors.initials: KS
authors.lastname: Lee
authors.forename: Byung-Tae
authors.initials: BT
authors.lastname: Kim
authors.forename: Joon Young
authors.initials: JY
authors.lastname: Choi
authors.forename: Young Mog
authors.initials: YM
authors.lastname: Shim
authors.forename: Chin A
authors.initials: CA
authors.lastname: Yi
mesh_terms: D000230:Adenocarcinoma / Q000175:diagnosis* / Q000000981:diagnostic imaging; D000328:Adult; D000368:Aged; D018277:Carcinoma, Mucoepidermoid / Q000175:diagnosis / Q000000981:diagnostic imaging; D018278:Carcinoma, Neuroendocrine / Q000175:diagnosis / Q000000981:diagnostic imaging; D002294:Carcinoma, Squamous Cell / Q000175:diagnosis* / Q000000981:diagnostic imaging; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D008297:Male; D008875:Middle Aged; D049268:Positron-Emission Tomography; D019275:Radiopharmaceuticals; D013945:Thymoma / Q000175:diagnosis* / Q000000981:diagnostic imaging; D013953:Thymus Neoplasms / Q000175:diagnosis* / Q000000981:diagnostic imaging; D014057:Tomography, X-Ray Computed
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18