Characterization of thymic masses using ¹⁸F-FDG PET-CT

Background: The resectability and survival may be improved in thymoma and thymic carcinoma with multimodality therapy. Various diagnostic imaging modalities are required for accurate diagnosis and preoperative staging of thymic masses. The present prospective study was planned to evaluate if Fluorodeoxyglucose (FDG) PET-CT can help differentiate various thymic lesions noted on conventional imaging modalities. Methods: A prospective study was undertaken in 23 patients who had shown either an anterior mediastinal mass consistent with thymic origin or suspicious for a thymic mass on contrast-enhanced computed tomography scan. All patients underwent whole body FDG PET-CT after intravenous injection of 370 MBq of FDG. The interpretation of PET-CT images was based on the following criteria: FDG uptake (present or absent), SUVmax, pattern of uptake, invasion to surrounding structures, presence of metastasis and necrosis. The results of PET-CT were correlated with the final histopathology following surgery. Statistical analysis was performed with SPSS 11.5 for Windows software. The mean SUVmax of the 3 groups of pathology was compared using the Kruskal-Wallis Test. Results: Thymic hyperplasia had an enlarged thymus with mean SUVmax of 1.1. Low risk thymoma had large tumors and their mean SUVmax was 3. High risk thymoma had small tumors with mean SUVmax of 2.1. As a group, thymoma had mean SUVmax value of 2.3. All thymic carcinomas were large, and their mean SUVmax was 7. The difference between the mean SUVmax for thymic hyperplasia, thymoma and thymic carcinoma was statistically significant. The difference between the SUVmax of high risk and low risk thymoma was not significant. Conclusion: ¹⁸F-FDG PET-CT can help characterize various thymic lesions noted on conventional imaging modalities. However, larger prospective studies are further required to substantiate these findings.