LYMPH-NODE INVOLVEMENT BY SPLENIC MARGINAL ZONE LYMPHOMA - MORPHOLOGICAL AND IMMUNOHISTOCHEMICAL FEATURES

Splenic marginal zone lymphoma (SMZL) has recently been proposed as a distinctive type of low-grade B-cell lymphoma. Although there is gener al agreement that this entity exists, its precise definition is blurre d by uncertainty in differential diagnosis from other low-grade B-cell lymphomas. There is even more uncertainty as to the histology of sple nic hilar and peripheral lymph nodes involved by SMZL. We therefore re viewed the histological and immunohistochemical features of 19 of thes e lymph nodes (14 hilar and five peripheral) from 14 cases of classica l SMZL and compared them with the features of lymph nodes involved by other B-cell lymphomas. The morphology and immunohistology of the lymp h nodes resemble those found in the white pulp of the spleen, showing a distinctive pattern, different from that which is observed in other B-cell lymphomas. In these cases, the overall architecture of the lymp h nodes is effaced and replaced by a nodular infiltrate, although the sinuses are preserved in most hilar lymph nodes. Some of the nodules c ontain a central reactive follicular center, around which there is a b road zone of small lymphocytes. In other cases, the central area is pa rtially infiltrated or, more commonly, totally replaced by these small lymphocytes, which in the periphery of the nodules showed a pale, sli ghtly larger cytoplasm. Scattered nucleolated blasts are present, larg ely confined to the periphery of the nodules. The tumoral cells expres s immunoglobulin (Ig)D, IgM, and Ig light chain restriction and show a low proliferation fraction. These findings confirm that SMZL is a rea l entity, and not merely a morphological pattern of splenic infiltrati on by different types of low-grade B-cell lymphoma.