Table 1 Differential diagnosis of mediastinal masses in children
Differential diagnosis | Diagnostic imaging modality | Comments | ||
|---|---|---|---|---|
Computed tomography | Magnetic resonance | PET scan | ||
Normal thymus | Quadrilateral with convex or straight margins in infants, triangular with concave or straight margins in older children | Bilobed, convex at birth, straight during puberty, concave in old age, greater generalized T1-weighted and fast spin-echo T2-weighted hyperintensity and diminishing intermediate T1- and T2-signal soft tissue with fatty involution | Homogeneous low-intensity uptake | Age-dependent change in appearance |
Benign Etiologies | ||||
Benign thymic hyperplasia | Symmetrically enlarged, typically homogeneous | Enlarged, thymus characteristics similar to normal thymus (see above) | Typically homogeneous low-intensity uptake | Idiopathic |
Thymic follicular hyperplasia | Symmetrically enlarged, normal sized in 25%-50% | Enlarged, thymus characteristics similar to normal thymus (see above) | Homogeneous uptake. | Chronic inflammatory states, autoimmune conditions, myasthenia gravis (65%-75%) |
Rebound hyperplasia | Symmetrically enlarged, normal sized in 25%-50% | Enlarged, thymus characteristics similar to normal thymus (see above) | Increased homogeneous uptake | After chemotherapy |
Thymolipoma | Pericardial fatty mass with fibrous septa | Hyperintense T1-signal resembling subcutaneous fat and area with intermediate intensity soft of tissue attenuation | Resembling uptake in fatty tissue and normal thymus | Mainly in adolescents and young adults |
Malignant Etiologies | ||||
Lymphoma | Homogeneous or heterogeneous, nodular, hemorrhage, necrosis, cystic components | Homogeneous low-signal on T1-weighted images, high-signal or intermixed areas (low and high) intensity on T2-weighted images | Heterogeneous intense uptake | Peak incidence in adolescence |
Teratoma | Well-circumscribed, displacing mass, calcification (80%), fat-fluid levels, cystic, heterogeneous changes in lung parenchyma, pleura, or pericardium (tumor rupture) | Hyperintense fat on T1-weighted images within fluid of low signal intensity (cystic changes), hyperintense mass on T2-weighted images | Heterogeneously avid | Tissue from germ-cell layers |
Seminoma | Large and lobular, homogenous | High-intensity mass with with septal structures in T2-weighted images | Heterogeneously avid | Most common primary solid tumor of the mediastinum |
Non-seminomatous tumor | Large, lobulated, heterogeneous masses with large (>50%) areas of low attenuation, hemorrhage, necrosis | Internal heterogeneous intensities with areas of high signal intensity reflecting degenerative cystic changes on T2-weighted images. | Heterogeneously avid | Highly aggressive |
Thyroid carcinoma | Well-defined, smooth or lobuated, tracheal deviation, contrast-enhancing, calcifications | Most tumors are hyperintense of markedly hyperintense on T2-weighted images | Heterogeneously avid | Ectopic thyroid |