Splenic marginal zone lymphoma is a lymphoma that infiltrates the marginal and mantle zones of splenic follicles [1-3]; whether the disease actually arises in splenic marginal zone memory B cells is uncertain . Analysis of immunoglobulin genes suggests that about one-third of cases arise in a pre-germinal-centre naïve B cell and the other two-thirds in a post-germinal-centre memory B cell. On-going immunoglobulin gene mutations occur .
Splenic lymphoma with villous lymphocytes is a morphological subset of splenic marginal zone lymphoma characterized by circulating lymphoma cells with fine cytoplasmic projections.
There is usually significant splenomegaly with minimal lymphadenopathy. In some patients the disease is associated with hepatitis C infection, this association being observed particularly around the Mediterranean area . Transformation to diffuse large B-cell lymphoma occurs in about 10% of cases.
Haematological and pathological features
The peripheral blood may be normal or there may be a moderate lymphocytosis with the lymphoma cells either being small lymphocytes with no distinguishing features or 'villous' lymphocytes; the latter have fine cytoplasmic projections, sometimes at one or both poles of the cell (Figures 10.1 and 10.2). Chromatin is condensed and sometimes there are small nucleoli. There may also be circulating plasmacytoid lymphocytes. Pancytopenia may be present as a result of splenomegaly and hypersplenism.
Peripheral blood film of a patient with splenic marginal zone lymphoma (splenic lymphoma with villous lymphocytes) showing rouleaux and two villous lymphocytes; one of the lymphocytes has a detectable Golgi zone. Romanowsky, x 100 objective.
Peripheral blood film of a patient with splenic marginal zone lymphoma (splenic lymphoma with villous lymphocytes) showing two nucleolated lymphocytes, one of which has villi at both poles of the cell. Romanowsky, x 100 objective.
Bone marrow infiltration, when present, may be interstitial, nodular or paratrabecular; a strikingly paratrabecular pattern of infiltration is less common than in follicular lymphoma. Occasionally, neoplastic cells surround a reactive germinal centre. Intra-sinusoidal infiltration, marked or subtle, is common. The presence of isolated intra-sinusoidal infiltration is particularly suggestive of this type of lymphoma.
Lymph node infiltration, e.g. in splenic hilar lymph nodes, is also around germinal centres.
Splenic infiltration is around pre-existing white pulp follicles (Figures 10.3, 10.4, 10.5, 10.6, 10.7, 10.8, 10.9), which are atrophic (Figure 10.10), and involves the marginal zone as well as the mantle zone . There is a distinct zoning of the infiltration with an outer paler zone being composed of larger cells with a high proliferative rate and an inner zone composed of smaller ...