Anatomical and Functional Compartments

Abstract

There is some variation in the structure of lymph nodes at different anatomical sites, but the histological compartments are the same and the variation is largely in their size. The typical lymph node structure is exhibited by cervical nodes which show the pattern of follicles, cortex, paracortex, medulla, and sinuses. These anatomical divisions also represent functional compartments in that the cortex, with its primary and secondary lymphoid follicles, is composed largely of B cells, whereas the paracortex comprises mostly T cells. The medullary sinuses are traversed by small vessels and represent the domain of histiocytes and plasma cells. Secondary follicles are identified by the presence of germinal centers with their larger and paler cells and are surrounded by an eccentric rim of small dark mantle cells. While the marginal zone is not visible in the resting lymph node, when hyperplastic, a marginal zone of post-germinal center B cells may be seen peripheral to the dark rim of mantle cells. The marginal zone cells are slightly larger than mantle cells and have more and paler cytoplasm. Unlike peripheral nodes, mesenteric nodes have more prominent sinuses with less conspicuous follicles and paracortex, and unstimulated axillary nodes have a rim of lymphoid tissue around a hilum of adipose tissue.