18F-FDG PET/CT of thymic epithelial tumors: usefulness for distinguishing and staging tumor subgroups.
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.
Sung
Yon Mi
YM
Department of Radiology and Center for Imaging Science, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
Lee
Kyung Soo
KS
Kim
Byung-Tae
BT
Choi
Joon Young
JY
Shim
Young Mog
YM
Yi
Chin A
CA
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
D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18