Extranodal and splenic small B-cell lymphoma.

Although almost any non-Hodgkin lymphoma can involve the spleen or an extranodal site as part of more widely disseminated disease, there is a group of small B-cell lymphomas that specifically arise in these locations. These are important to recognise as some appear to have a behaviour and prognosis that is distinct from their nodal counterparts. In addition, there are entities that are specific to extranodal locations (such as extranodal marginal zone lymphoma) and to the red or white pulp of the spleen. In this review, the characteristics of these entities will be presented as well as clues to help distinguish lymphoma from reactive infiltrates in extranodal sites and measure to distinguish between small B-cell lymphomas encountered in the spleen and at extranodal locations.