Bone marrow trephine biopsies are an integral part of the diagnosis, staging and follow-up of patients with haematologic disorders. Lymphoid nodules are a common finding, usually reported in association with chronic inflammatory syndromes, infection haemolysis, myeloproliferative disorders and autoimmune diseases. They are usually considered to be a reactional feature. As bone marrow is the most common site of extranodal involvement of follicular lymphoma, the most important differential diagnosis is represented by bone marrow involvement by malignant lymphoma. From a practical point of view bone marrow lymphoid infiltrates are easy to diagnose on a histological basis. Benign aggregates are typically smaller, well distinguishable, contain a mixed population of cells and are nonparatrabecular. Neoplastic aggregates involving bone marrow as a paratrabecular infiltrate composed of cleaved cells. Immunophenotyping using a panel of monoclonal antibodies is capable of determining the lineage, subset and stage of differentiation of neoplastic lymphoid cells and may therefore contribute to confirm diagnosis. Especially in controversial cases, immunogenotypic analysis of the lymphoid proliferation may be helpful. Monoclonality may be detected by monotypic expressions of immunoglobulins or clonal rearrangements in the immunoglobulin heavy chain or T cell receptor genes. Ideally, the results of immunogenotypic analysis should be interpreted only in conjunction with the results of morphologic evaluation and immunophenotypic analysis. Morphology is still the gold standard in evaluating bone marrow infiltration by follicular lymphoma and immunophenotypic and immunogenotypic analysis should be considered as useful complementary investigations.
Lymphoid nodules; bone marrow; immunophenotyping; immunogenotyping
