Ultrastructural diagnosis of lymphomas and leukemias

Scanning and transmission electron microscopy of clonal peripheral blood lymphocytes in low grade non-Hodgkin's B-cell lymphomas with predominant splenomegaly

Peripheral blood mononuclear cells (PBLs) from 14 patients with low grade non-Hodgkin's B-cell lymphomas with predominant splenomegaly were studied by means of scanning (SEM) and transmission electron microscopy (TEM). All patients had peripheral blood and bone marrow involvement, the absence of lymphoadenopathy, and, except in one case, immunophenotypic features of a malignant proliferation of mature spleen B-cells arising from outside the germinal center, but not consistent with CLL or HCL. Several distinctive cytological features were observed in PBLs of the different subgroups. The SEM surface features of PBLs in patients with intermediate differentiation lymphocytic lymphoma (IDL) (five cases), lymphoplasmacytoid immunocytoma (LP-IC) (two cases), and mixed small and large cells malignant lymphoma (one case) were characterized by the presence of numerous well-developed microvilli. Some distinctive TEM ultrastructural features were also seen in the different cases. In the two cases of splenic lymphoma with villous lymphocytes (SLVL), SEM revealed large and elongated surface microvilli generally arising from two or three poles of the cells. This surface morphology, confirmed by TEM analysis, may be pathognomonic of this disease. Four additional cases, tentatively classified as small lymphocytic lymphoma on the basis of immunophenotypic data, were extremely heterogeneous at both SEM and TEM analysis. The ultrastructural features revealed by SEM and TEM may be useful for the more precise characterization of this heterogeneous group of diseases, which is generally difficult to define even when immunophenotypic and molecular approaches are used.

Lymphomas of the mediastinum

The purpose of this clinicopathologic overview is to describe the types of lymphomas that present in the mediastinum. A comparison of the frequency of the different subtypes of lymphoma that are found in children and adults is provided. In general, immunohistochemistry and immunophenotyping studies are essential to the laboratory workup of neoplasms presenting in the mediastinum. An assessment of proliferative index in lymphoma is most helpful to determine tumor aggressiveness and patient prognosis. Electron microscopy is most helpful in the differential diagnosis of mediastinal neoplasms, where lymphomas may be distinguished from nonlymphomatous neoplasms using key ultrastructural features. The role of electron microscopy in the subclassification of lymphomas is mostly academic, with a few exceptions. The varied ultrastructural appearance of Hodgkin's cells and of different subtypes of non-Hodgkin's lymphoma is illustrated, using cases from our patient files. An ultrastructural study of lacunar cells in Hodgkin's disease provides evidence that the formation of lacunae may have a structural and/or physiologic basis. Mummified cells showing some of the features of a physiologic form of cell death, called apoptosis, are also described.