(18)F-FDG PET for the evaluation of thymic epithelial tumors: Correlation with the World Health Organization classification in addition to dual-time-point imaging.

PURPOSE

Our aim was to determine dual-phase (18)F-FDG PET imaging features for various subtypes of thymic epithelial tumors based on the World Health Organization classification.

METHODS

Forty-six patients with histologically verified thymic epithelial tumors [23 with low-risk tumors (4 with type A, 16 with AB, and 3 with B1) and 23 with high-risk tumors (7 with B2, 5 with B3, and 11 with thymic carcinoma] were enrolled in this study. All patients were injected with (18)F-FDG.; after 1 h, they underwent scanning; after 3 h, 23 patients underwent an additional scanning. The maximum standard uptake value (SUV(max)) and the retention index (RI%) of the lesions were determined.

RESULTS

The early and delayed SUV(max) values in the patients with high-risk tumors [early SUV(max) (mean: 6.0) and delayed SUV(max) (mean: 7.4)] were both significantly larger than those in patients with low-risk tumors [early SUV(max) (mean: 3.2) and delayed SUV(max) (mean: 3.4)] (P < 0.05). Early SUV(max) values of greater than 7.1 differentiated thymic carcinomas from other types of tumors. For the histological differentiation between high-risk tumors and low-risk tumors, an early SUV(max) value of 4.5 was used as the cutoff. The sensitivity, specificity, and accuracy were 78.3, 91.3, and 84.8%, respectively.

CONCLUSION

High SUV values (early SUV > 4.5) suggest the presence of high-risk tumors. A very high SUV value (early SUV > 7.1) is useful for the differentiation of thymic carcinomas from other types of tumors. The delayed SUV values were higher than the early SUV values in all types of tumors.