Intrasinusoidal bone marrow involvement by splenic lymphoma with villous lymphocytes: a helpful immunohistologic feature.

: Splenic lymphoma with villous lymphocytes (SLVL) is a chronic monoclonal B-cell lymphoproliferative disorder characterized by massive splenomegaly and typical villous lymphocytes in the peripheral blood (PB). The diagnosis of SLVL relies on blood smear examination, phenotypic features, and marginal zone involvement of the spleen. The histologic pattern of bone marrow (BM) involvement has not been well characterized. We report four cases associated with a peculiar intrasinusoidal BM involvement. This intrasinusoidal pattern was highlighted by immunostaining that also showed the cytoplasmic projections of villous lymphocytes within routinely fixed and decalcified BM biopsy specimens. Therefore, a simple immunohistochemical analysis of BM involvement would help to identify SLVL. Combined with cytologic and immunophenotypic evaluation of marrow and blood smears, this intravascular pattern might be helpful in differentiating SLVL from hairy cell leukemia and its variant. Whether this peculiar intravascular pattern combined with cytologic evaluation represents a practical alternative to the diagnostic splenectomy must be confirmed by extensive studies focusing on this immunohistochemical criterion.