Small lymphoid proliferations in extranodal locations

Abstract

Context. - Low-grade non-Hodgkin lymphomas frequently involve extranodal sites including the gastrointestinal tract, skin, and lung, either selectively or as part of wide-spread dissemination. Differentiation from inflammatory or infectious conditions requires knowledge of specific histologic characteristics of the various entities as well as ancillary techniques. Objective. - To describe the key features and provide diagnostic clues to the identification of specific exiranodal low-grade lymphomas of T-cell and B-cell types including small lymphocytic lymphoma, follicular lymphoma, mantle cell lymphoma, extranodal marginal zone B-cell lymphomas of mucosal-associated lymphoid tissue, and hairy cell leukemia. Histologic and cytologic features are highlighted, as well as appropriate integration of results of ancillary diagnostic studies including flow cytometry, immunohistochemistry, molecular features, and cytogenetics. Data Sources. - The published literature as well as personal experience from a specialized hematopathology practice at a large university medical center. Conclusions. - Correct identification of extranodal low-grade lymphomas and differentiation from hyperplastic and inflammatory or infectious processes require the ability to distinguish each of the specific entities discussed. Ancillary studies are often indispensable in reaching a correct diagnosis.