A MARGINAL ZONE PATTERN MAY BE FOUND IN DIFFERENT VARIETIES OF NON-HODGKINS-LYMPHOMA - THE MORPHOLOGY AND IMMUNOHISTOLOGY OF SPLENIC INVOLVEMENT BY B-CELL LYMPHOMAS SIMULATING SPLENIC MARGINAL ZONE LYMPHOMA

Aims: Splenic marginal zone lymphoma (SMZL) is characterized by a micr onodular infiltrate of the splenic white pulp. centred on pre-existing follicles, with a peripheral rim of 'marginal' zone B-cells, always a ccompanied by a variable degree of red pulp infiltration;These histolo gical features can be closely mimicked by a variety of other small B-c ell lymphomas when they involve the spleen, which makes recognition of SMZL difficult. We therefore have compared the histopathological and immunohistochemical features of other non-Hodgkin's lymphoma (NHL) typ es with those of SMZL. Methods and results: We selected cases of splen ic involvement by different types of B-cell lymphoma. including mantle cell lymphoma (MCL), follicular lymphoma (FL), immunocytoma (IM) and lymphocytic lymphoma (B-CLL). A micronodular pattern and marginal zone differentiation were both found to be frequently present in FL and MC L, and with lesser frequency in IM and B-CLL, The main morphological f eature useful for differential diagnosis was the cytological compositi on of the white pulp tumoral nodules, SMZL, is distinguished by charac teristic dimorphic cytology, different from the monomorphic cytology o f MCL, and the distinctive mixture of centroblasts and centrocytes whi ch is the rule in FI,, B-CLL could also be identified on the basis of the polymorphic cytology including small lymphocytes and prolymphocyte s, whereas cases diagnosed as IM show prominent plasmacytic differenti ation, lacking the features of the other lymphoma types, Immunohistoch emistry was particularly useful for the differential diagnosis, Thus t he recognition of MCL was facilitated by the identification of cyclin D1 and CD43 reactivity: while FL could be recognized by the lack of Ig D expression or the distinctive pattern of Ki67 staining found in SMZL , B-CLL cells were CD23+, CD43+. Conclusion: The results of this study provide morphological and immunohistological information useful in th e recognition of the different varieties of NHLs when involving the sp leen and the differential diagnosis of SMZL.