Immunohistochemistry for tDt is negative. This finding is consistent with the stated diagnosis.
Biopsy of superior mediastinal lymph node x2.
Specimen container labelled 'superior mediastinal lymph node'. Specimen consists of 4 irregular fragments of yellow tan tissue between 4mm and 7mm.
Sections of the mediastinal lymph nodes show diffuse effacement of the architecture with extension of the lymphoid infiltrate into adjacent extranodal fat. Some biopsies are affected by crush artefact. In better preserved areas there is a mixed population of lymphocytes, histiocytes and eosinophils, including increased numbers of large cells with irregular nuclear contours, conspicuous nucleoli and pale vacuolated cytoplasm, forming sheets. No Reed-Sternberg cells are seen.
Immunohistochemistry confirms the presence of sheets of CD20 positive, PAX5 positive atypical B cells, admixed with background small CD3 positive T cells. There is patchy weak CD23 expression. No tDt or CD30 positive cells are seen. CD15 expression is limited to neutrophils. There is non-specific Cyclin D1 expression in endothelial cell nuclei. The Ki67 index of the atypical lymphoid infiltrate is estimated to be about 80%. EBER CISH is negative.
The features are consistent with a non-Hodgkin lymphoma, favouring either a primary mediastinal large B cell lymphoma or diffuse large B-cell lymphoma. There are morphological features such as compartmentalising sclerosis and cytoplasmic pallor to the tumour cells that favour the former diagnosis, but the immunophenotype does not distinguish between these two entities. Clinicoradiological correlation regarding any previous history of lymphoma and whether the disease is limited to the mediastinum would be helpful to confirm the diagnosis. Ig gene rearrangement studies or flow cytometry would also be useful to confirm clonality.
Superior mediastinal lymph nodes - non-Hodgkin large B cell lymphoma.
Some features suggest primary mediastinal large B cell lymphoma, but the differential diagnosis also includes diffuse large B cell lymphoma (see comment above).
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