Chapter 21: Hematopoietic Pathology

Hematopoietic Pathology details the pathophysiology of lymphadenopathy, differentiating between acute and chronic nonspecific lymphadenitis and specific conditions like cat-scratch fever. A significant portion of the chapter is dedicated to the WHO classification of lymphoid neoplasms, extensively covering mature B-cell neoplasms such as Chronic Lymphocytic Leukemia and Small Lymphocytic Lymphoma, which are characterized by CD5 and CD23 markers and smudge cells. It contrasts these with Hairy Cell Leukemia, noted for TRAP positivity, and aggressive malignancies like Diffuse Large B-Cell Lymphoma and Burkitt Lymphoma, the latter associated with the t(8;14) translocation and a starry-sky histological pattern. The discussion includes Follicular Lymphoma, driven by BCL2 overexpression via t(14;18), and Mantle Cell Lymphoma involving cyclin D1. The chapter rigorously examines plasma cell dyscrasias, specifically Multiple Myeloma, highlighting clinical features such as lytic bone lesions, hypercalcemia, and M proteins, while distinguishing it from Monoclonal Gammopathy of Undetermined Significance and Waldenstrom Macroglobulinemia. T-cell malignancies, including Adult T-cell Leukemia/Lymphoma and Mycosis Fungoides, are also reviewed. The text differentiates Hodgkin Lymphoma from non-Hodgkin types by the presence of diagnostic Reed-Sternberg cells, contiguous spread, and specific subtypes like nodular sclerosis. Furthermore, the chapter details Acute Leukemias, contrasting Acute Lymphoblastic Leukemia, which is common in children and TdT positive, with Acute Myelogenous Leukemia, characterized by myeloblasts with Auer rods and specific genetic fusions like PML/RARA. The summary concludes with an analysis of Myeloid Neoplasms, including Myelodysplastic Syndromes and Myeloproliferative Neoplasms such as Chronic Myelogenous Leukemia, which is associated with the Philadelphia chromosome t(9;22), Polycythemia Vera, and Myelofibrosis, alongside brief discussions on splenic disorders, thymomas, and Langerhans cell histiocytosis.