Lymphadenopathy - Anatomy and Pathology
Lymphadenopathy is an acute or chronic abnormal state of either size or consistency of the lymph nodes; it is a response to infection, inflammation, or malignancy. The body has approximately 600 lymph nodes, but only those in the submandibular, axillary or inguinal regions are normally palpable in healthy individuals. Normal nodes are usually less than 1.0 cm in diameter and tend to decrease or remain stable in size. Lymphadenitis is defined as an acute or chronic inflammation of lymph nodes. Lymphangitis is defined as an inflammation of lymphatic channels, usually in the subcutaneous tissues.
Lymph nodes are oval bean-shaped structures. Each lymph node is enclosed by a fibrous capsule. Lymph moves into a node via different lymphatic vessels and emerges by one or two efferent vessels. Fibrous septa or trabeculae extend from the covering capsule toward the center of the node. When an infection is present, germinal centers form and the node begins to release lymphocytes. If this barrier of host resistance is overcome, the infectious process may spread to more distant nodes or to the blood stream.
PATHOGENESIS AND PATHOLOGY
The lymph nodes participate in the filtration of microorganisms, the production of antibody, and the processing of lymphocytes within the human body. With the exception of neoplasia, lymph nodes are rarely the site of primary disease. However, they are involved in virtually all infectious processes. When a local infection occurs, the regional lymph nodes react to the invading microorganisms. If this barrier of host resistance is overcome, the infectious process may spread to more distant nodes or to the blood stream. Generalized lymphadenopathy and reticuloendothelial system hyperplasia can occur secondary to widespread sepsis.
Lymph nodes enlarge because of lymphocyte proliferation or macrophage hyperplasia resulting from infiltration of microorganisms or malignant cells, antigenic interaction, or neoplastic proliferation of lymphocytes or phagocytes. Macroscopically, the nodes of acute nonspecific lymphadenitis become swollen, gray-red, and engorged. Histologically, lymphoid follicles are prominent, with large germinal centers containing numerous mitotic figures. When bacteria are the cause of the reaction, the centers of the follicles may undergo necrosis with suppuration. With less severe reactions, there is a neutrophilic infiltrate about the follicles, and numerous neutrophils can be found within the lymphoid sinuses. The cells lining the sinuses become hypertrophied and often undergo hyperplasia.
Acutely inflamed nodes become enlarged because of cellular infiltration and edema. If capsular distension is marked, tenderness may be present. The nodes may become fluctuant if invaded by bacteria. Chronic inflammation can be manifested by enlarged nodes with mononuclear cell infiltration.
Lymphadenopathy can be categorized as (a) acute or chronic, (b) local or generalized, and (c) with or without specific histology. Most patients who present with lymphadenopathies have acute, localized processes, and biopsy of the involved nodes show nonspecific histology, and are classified as regional nonspecific lymphadenitis.