Histotopographical characterization of the para-aortic lymph nodes in the area near the origin of the thoracic duct, and its relationship to nodal cancer metastasis

摘要

Using 10 elderly cadavers without macroscopically evident tumors, we histologically examined 115 para-aortic lymph nodes located near the origin of the thoracic duct after preparation of en bloc specimens using a clearance method. The afferent and efferent sides of these nodes were usually not discriminated clearly because i) the superficial cortex (B-lymphocyte area) and deep cortex (T-lymphocyte area) were not clearly differentiated due to lack of a typical hilus, and both cortices were intermingled to form "nodular masses"; ii) each nodule with a lining of macrophages was surrounded by dilated intermediate and subcapsular sinuses; iii) the nodes were often surrounded by multiple tributaries of the thoracic duct. Moreover, the nodes sometimes involved these tributaries inside. Therefore, the nodal architecture seemed to accelerate intranodal shunt flow without filtration through the cortex. Valves of the lymphatic vessel tended to be restricted to an area immediately before drainage into the thoracic duct. Thus, lymph flow was likely to change along a network of tributaries around a node. These morphologies suggested very limited barrier function of the para-aortic node against cancer metastasis. However, we hypothesized that "better" or "worse" types of nodes are histologically identifiable when they are picked up surgically along with the surrounding tissues.