FDG-PET/CT Skull Base to Mid-Thigh Fluorine-18-2-fluoro-2-deoxy-D-glucose (FDG)-PET/CT offers that of conventional CT in the initial 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. 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 Imaging of Mediastinal Masses thymic cysts can also be FDG-PET/CT-avid [42]. Combined use of FDG-PET/CT and dynamic contrast-enhanced (DCE) MRI has been shown to be helpful to distinguish prevascular mediastinal solid tumors from one another [55]. Higher standardized uptake values (SUVs) on FDG-PET/CT are more frequently found in high-risk thymoma, thymic carcinoma, and lymphoma than in low-risk thymoma [55-57]. Cross-sectional imaging by MRI remains superior to CT for detection of invasion of the mass across tissue planes, including the chest wall and diaphragm, and involvement of neurovascular structures, secondary to its higher soft- tissue contrast [48-52]. As a supplement to static assessment of tissue plane transgression, dynamic MRI [45-48] during free-breathing or cinematic cardiac gating can be performed to assess movement of the mass relative to adjacent structures, confirm or exclude adherence of the mass to adjacent structures, and observe diaphragmatic motion in real time [80-84]; paradoxical motion or lack of motion can indicate phrenic nerve involvement by the mediastinal mass, without the need to perform a subsequent fluoroscopic sniff test.
Imaging of Mediastinal Masses. FDG-PET/CT Skull Base to Mid-Thigh Fluorine-18-2-fluoro-2-deoxy-D-glucose (FDG)-PET/CT offers that of conventional CT in the initial 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. 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 Imaging of Mediastinal Masses thymic cysts can also be FDG-PET/CT-avid [42]. Combined use of FDG-PET/CT and dynamic contrast-enhanced (DCE) MRI has been shown to be helpful to distinguish prevascular mediastinal solid tumors from one another [55]. Higher standardized uptake values (SUVs) on FDG-PET/CT are more frequently found in high-risk thymoma, thymic carcinoma, and lymphoma than in low-risk thymoma [55-57]. Cross-sectional imaging by MRI remains superior to CT for detection of invasion of the mass across tissue planes, including the chest wall and diaphragm, and involvement of neurovascular structures, secondary to its higher soft- tissue contrast [48-52]. As a supplement to static assessment of tissue plane transgression, dynamic MRI [45-48] during free-breathing or cinematic cardiac gating can be performed to assess movement of the mass relative to adjacent structures, confirm or exclude adherence of the mass to adjacent structures, and observe diaphragmatic motion in real time [80-84]; paradoxical motion or lack of motion can indicate phrenic nerve involvement by the mediastinal mass, without the need to perform a subsequent fluoroscopic sniff test.