FDG-PET/CT Skull Base to Mid-Thigh Unless the degree of metabolic activity of a mediastinal mass is sought and deemed capable of changing clinical management, FDG-PET/CT would be unlikely to add diagnostic information regarding a mediastinal mass beyond that offered by MRI. FDG-PET/CT offers limited additional value beyond that of conventional CT and MRI in the assessment of mediastinal masses [53], with the exception of its use for primary mediastinal lymphoma staging and surveillance and detection of metastatic lymphadenopathy, the latter of which is not within the scope of this topic. FDG-PET/CT has become the standard for staging and assessment of treatment response for lymphomas that are FDG-PET-avid at baseline or at the time recurrence [91-97]. A caveat is that although a negative surveillance FDG- PET/CT is reassuring of a good outcome, a positive FDG-PET/CT can be misleading, as it does not always implicate Imaging of Mediastinal Masses residual or recurrent lymphoma [96,98]. With regard to prevascular mediastinal masses, a negative FDG-PET/CT has been shown to be helpful in excluding malignancy; however, a positive FDG-PET/CT has little value for discrimination between benign and malignant lesions [53]. The frequent FDG-PET/CT avidity of normal and hyperplastic thymus [54] is a confounder in FDG-PET/CT assessment of the prevascular mediastinum. Benign thymic cysts can also be FDG-PET/CT-avid [42]. Combined use of FDG-PET/CT and DCE MRI has been shown to be helpful to distinguish prevascular mediastinal solid tumors from one another [55]. Higher SUVs on FDG- PET/CT are more frequently found in high-risk thymoma, thymic carcinoma, and lymphoma than in low-risk thymoma [55-57]. FDG-PET/CT appears to be more sensitive than CT alone for detection of mediastinal recurrence of thymoma [99].
Imaging of Mediastinal Masses. FDG-PET/CT Skull Base to Mid-Thigh Unless the degree of metabolic activity of a mediastinal mass is sought and deemed capable of changing clinical management, FDG-PET/CT would be unlikely to add diagnostic information regarding a mediastinal mass beyond that offered by MRI. FDG-PET/CT offers limited additional value beyond that of conventional CT and MRI in the assessment of mediastinal masses [53], with the exception of its use for primary mediastinal lymphoma staging and surveillance and detection of metastatic lymphadenopathy, the latter of which is not within the scope of this topic. FDG-PET/CT has become the standard for staging and assessment of treatment response for lymphomas that are FDG-PET-avid at baseline or at the time recurrence [91-97]. A caveat is that although a negative surveillance FDG- PET/CT is reassuring of a good outcome, a positive FDG-PET/CT can be misleading, as it does not always implicate Imaging of Mediastinal Masses residual or recurrent lymphoma [96,98]. With regard to prevascular mediastinal masses, a negative FDG-PET/CT has been shown to be helpful in excluding malignancy; however, a positive FDG-PET/CT has little value for discrimination between benign and malignant lesions [53]. The frequent FDG-PET/CT avidity of normal and hyperplastic thymus [54] is a confounder in FDG-PET/CT assessment of the prevascular mediastinum. Benign thymic cysts can also be FDG-PET/CT-avid [42]. Combined use of FDG-PET/CT and DCE MRI has been shown to be helpful to distinguish prevascular mediastinal solid tumors from one another [55]. Higher SUVs on FDG- PET/CT are more frequently found in high-risk thymoma, thymic carcinoma, and lymphoma than in low-risk thymoma [55-57]. FDG-PET/CT appears to be more sensitive than CT alone for detection of mediastinal recurrence of thymoma [99].