LymphNodes
Summary
Lymph nodes are small, encapsulated secondary lymphoid organs located along lymphatic vessels that filter lymph and serve as sites for immune cell activation. They are organized into cortex (B-cell follicles), paracortex (T-cell zone), and medulla (plasma cells, macrophages). Enlargement (lymphadenopathy) can indicate infection, autoimmune disease, or malignancy, and specific nodal drainage patterns help localize pathology.
Detail
Lymph nodes are bean-shaped structures distributed throughout the body along the lymphatic system, functioning as filters that trap antigens, pathogens, and foreign particles from lymphatic fluid. Structurally, each node has an outer cortex containing primary and secondary (germinal center) follicles rich in B lymphocytes and follicular dendritic cells, a paracortex housing T lymphocytes and interdigitating dendritic cells (this region enlarges in viral infections and is dependent on T-cell activity, notably atrophying in conditions like DiGeorge syndrome), and an inner medulla with medullary cords containing plasma cells and macrophages, plus medullary sinuses that allow lymph drainage into efferent lymphatics.
Lymph enters via afferent lymphatic vessels, percolates through subcapsular, cortical, and medullary sinuses lined by macrophages that phagocytose antigens, and exits via efferent vessels at the hilum, alongside nodal artery and vein.
Clinically, lymphadenopathy is a key diagnostic clue. Reactive/hyperplastic nodes (tender, mobile, soft) suggest infection—follicular hyperplasia indicates humoral (B-cell) response as in bacterial infections, while paracortical hyperplasia suggests viral infections (e.g., EBV, HIV) or vaccination. Painless, firm, fixed, matted nodes raise concern for malignancy—either metastatic carcinoma (subcapsular sinus involvement typically) or lymphoma (diffuse effacement). Specific lymph node stations have clinical significance: Virchow's node (left supraclavicular) suggests intra-abdominal or thoracic malignancy (classically gastric cancer); Sister Mary Joseph nodule involves periumbilical lymphatics from intra-abdominal cancer spread. Sentinel lymph node biopsy is used clinically to stage cancers like breast cancer and melanoma by identifying the first draining node.
High-yield associations include cat-scratch disease (Bartonella henselae) causing regional lymphadenitis, tuberculous lymphadenitis (scrofula), and node biopsy findings such as Reed-Sternberg cells in Hodgkin lymphoma or starry-sky pattern in Burkitt lymphoma.
Sources
- Robbins and Cotran Pathologic Basis of Disease
- First Aid for the USMLE Step 1
- Junqueira's Basic Histology
- Kumar, Abbas, Aster - Robbins Basic Pathology
Reviewed by AnkiBoss editorial — medical student review. Information here is for study reference only and is not medical advice. Spotted an error? Let us know.