Follicular lymphoma transforming into diffuse large B-cell lymphoma in spleen: Simultaneous appearance of both on 18F-FDG PET/CT and histology.

Low grade lymphoma may transform into a more aggressive lymphoma and this transformation is usually associated with a poor outcome. A 65year old man presented with two metabolically active splenic lesions on a staging [18F] fluoro-2-deoxy-d-glucose (18F-FDG) positron emission tomography/computed tomography (PET/CT). Histologic evaluation post splenectomy confirmed the presence of two clonally related lymphomas: a follicular lymphoma (FL) and a diffuse large B-cell lymphoma (DLBCL). Molecular genetic studies confirmed that the DLBCL lesions arose from a pre-existing FL. We present the 18F-FDG PET/CT imaging characteristics of both lymphoma types which were simultaneously present in the spleen.