Completion CT staging of the abdomen and pelvis was unremarkable. The patient underwent an US-guided biopsy of the superior mediastinum mass. 

Histopathology report

MACROSCOPIC DESCRIPTION: 1. "Chest biopsy": One cream core biopsy up to 9mm. A1. 2. "Chest Bx": One cream core biopsy up to 8mm. A1. (SEK)

MICROSCOPIC DESCRIPTION: 1&2. Sections show cores of tissue containing a dense mixed cellular infiltrate comprising large atypical cells with admixed small regular appearing mononuclear cells. The large aberrant cells have elongate sometimes folded nuclei with prominent nucleoli, occasional bilobed nuclei and indistinct cytoplasm. In areas the large cells are the predominant cell type and form sheets. There are many apoptotic cells. There is necrosis at the end of one of the biopsies. There is patchy, fine fibrous stroma without obvious compartmentalization. The admixed mononuclear cells mostly appear to be lymphocytes. There are occasional neutrophils. One eosinophil is noted. By immunohistochemistry the large cells are CD45+, CD20+, CD79a+, PAX5+, CD30+(focal and weak), CD15-, CD3-, ALK1-, EBV-LMP-, EBV-CISH-, CD23+, bcl6+, CD5-, EMA-. Fascin is difficult to interpret.

DIAGNOSIS: 1&2. Mediastinal mass biopsies: Large B-cell lymphoma with features favoring Primary mediastinal large B-cell lymphoma.