Chapter 6 - Reactive Lymphadenopathies

Abstract

The reactive lymphadenopathies represent hyperplasia of different lymph node components and therefore demonstrate particular structural patterns such as follicular hyperplasia, paracortical hyperplasia, sinus histiocytosis, granulomas, or a mixed pattern. In follicular hyperplasia, the lymph node enlargement is primarily due to the increased number and size of the follicles. Germinal centers are expanded and follicles appear in different sizes and shapes and are surrounded by well-defined mantle zones. Follicles occupy cortical, paracortical, and even sometimes medullary zones, but they are usually separated from one another by interfollicular lymphoid tissues. Lymphadenitis with paracortical pattern is characterized by the expansion of the interfollicular areas with a mixture of small lymphocytes, immunoblasts, and increased high endothelial venules. T-cells are the predominant cell type, but there are variable numbers of B-immunoblasts and plasma cells. In addition Sinus histiocytosis with massive lymphadenopathy is a bilateral, painless, massive cervical lymphadenopathy reported in patients under the age of 20 years. The affected lymph nodes show a characteristic feature consisting of sheets of large sinus histiocytes with abundant clear or foamy cytoplasm containing numerous lymphocytes. Further certain types of reactive lymphadenitis demonstrate a combination of follicular, paracortical, and/or sinus patterns. Examples are dermatopathic lymphadenitis, toxoplasmosis, Kikuchi's disease, and Kimura's disease.