Malignant versus benign mediastinal tumors: Quantitative assessment with various PET parameters

Objectives Solid malignant and benign mediastinal tumors often appear similar on CT and MRI. FDG PET/CT may be helpful for characterizing the tumors. We aimed to evaluate the efficacy of adding volumetric parameters and the information of intratumoral heterogeneity of FDG uptake to maximum standardized uptake values (SUVmax) alone for differentiating benign from malignant mediastinal tumors.

Methods Thirty-seven mediastinal tumors (25 benign and 12 malignant) were examined. The study included thymomas in 14 pts, thymic cyst in 9, malignant lymphoma in 4, and others in 10.SUVmax, metabolic tumor volume (MTV), and total lesion glycolysis (TLG) were measured for each tumor. MTV was defined as the volume showing SUV 2.5 or more. Cumulative SUV-volume histograms (CSH), describing % of total tumor volume above % threshold of SUVmax were calculated for tumors showing SUV 2.5 or more. The area under a CSH curve (AUC) was used as a heterogeneity index. Comparison between PET measurements was performed with Mann-Whitney U test. Diagnostic accuracy of each PET parameter using different cut-off values that best differentiated between benign and malignant tumors was evaluated.

Results Fourteen mediastinal tumors showed SUVmax 2.5 or more (7 benign and 7 malignant). The median SUVmax,MTV and TLG in the benign group were 2.1±1.3,16.7±27.6ml and 60.2±106.8g, while those in the malignant group were 6.7±4.5, 79.8±79.3ml and 60.2±106.8g, respectively. The differences were significant (P<0.05 for all). However, the difference between the AUC-CSH of the two groups was not significant. Sensitivity, specificity and accuracy for mediastinal tumors were 75.0, 88.0, and 83.8 % using cut-off SUVmax of 3.3, and 100, 85.7, and 92.9% using cut-off MTV of 28.4ml or TLG of 76.7g.

Conclusions Volumetric parameters (MTV and TLG) appeared to provide additional information in differentiating benign and malignant mediastinal tumors over SUVmax alone.