Figure 1
(A) Axial cross section on cardiac CTA showing the well circumscribed mass (red arrow) anterior to the right atrial appendage and adjacent to the pericardium. (B) A 3-dimensional reconstructed CT image of the mass with arterial supply from the right internal mammary artery (yellow arrow). (C, D) CMR images show the mass with significant first-pass perfusion and late gadolinium enhancement consistent with a highly vascularized structure.
Figure 2
Morphologic analysis of the mediastinal mass. (A) On gross examination, the specimen consists of a single portion of fibroadipose tissue (10.5 × 7.5 × 1.8 cm; 65 gm). (B) Serial sectioning reveals a well-circumscribed, tan-red mass (4.0 × 2.4 × 2.0 cm) that is predominantly solid with some focal cystic areas. The margins appeared grossly free of tumor. (C) The tumor is composed of one large, solid nodule with a thin, fibrous capsule abutting fatty, fibrous thymic tissue. (D) The tumor nodule is characterized by multiple variably sized tumor nests surrounded by an abundant lymphoid stroma. (E) There is a distinct boundary between medullary-type epithelial cells and lymphoid stroma. (F) Tumor nests are composed of spindled to ovoid cells with moderate atypia and rare mitoses.
Figure 3
Immunostaining staining of the mediastinal mass. (A) The epithelial cells in the tumor nest are diffusely positive for CK (AE1/AE3), (B) patchy positive for CD117, and (C) negative for CD5. (D) Stromal T lymphocytes are positive for TDT and (E) CD3. (F) CD20 highlights mature B cells within the lymphoid stroma.