A practical approach to small lymphoid cell infiltrates in the lower gastrointestinal tract

The intestines contain the largest accumulation of lymphoid tissue in the body. Hence it is not surprising that a variety of lymphoid lesions are found here. The spectrum ranges from focal or diffuse reactive lymphoid hyperplasias to post transplant lymphoproliferative disorders to full-blown lymphomas. In fact, the GI tract is the most common extranodal site of non-Hodgkin lymphoma (NHL), often arising in a setting of immunosuppression or immune dysregulation. The distinction therefore, of reactive lesions from low grade NHLs especially the small cell type, is of clinical significance, as the management is different. The diagnosis in these lymphoid lesions is best made through familiarity with the histologic patterns of injury, systematic approach to diagnosis and full knowledge of the clinical setting. This review will provide an overview of the normal mucosal immune system and discuss the lymphoid pathology of the lower GIT with emphasis on a practical approach to small cell infiltrates.