# Lymph Node Histology > Lymph node histology for MBBS Anatomy: cortex and paracortex, germinal centres, medullary cords, sinus flow and tuberculosis microcopy patterns. - Canonical URL: https://prepelephant.com/topics/mbbs/anatomy/lymph-node-histology - Exam / course: MBBS · Subject: Anatomy - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Lymph Node Histology", PrepElephant, https://prepelephant.com/topics/mbbs/anatomy/lymph-node-histology ## Direct answer A lymph node is a bean-shaped filter with a strict internal traffic plan: lymph enters through multiple afferent vessels on the convex surface, floods the subcapsular (marginal) sinus, percolates through cortical and medullary sinuses, and leaves through efferent vessels at the hilum — so anything in the lymph meets the cellular immune system before it reaches the blood. The cortex holds B lymphocytes in spherical follicles, primary follicles at rest and secondary follicles with pale germinal centres when activated; the paracortex beneath holds T lymphocytes around high endothelial venules through which recirculating lymphocytes enter from blood; and the medulla consists of plasma-cell-rich cords separated by sinuses that converge on the hilum. A fibrous capsule with trabeculae and a reticular fibre scaffold holds it all, and the histology of an enlarged node often names the disease — caseating granulomas for tuberculosis, sinus histiocytosis for draining carcinoma. ## What you must remember - **Flow sequence:** afferent lymphatics (multiple, convex surface) to subcapsular sinus to trabecular (cortical) sinuses to medullary sinuses to efferent vessels at the hilum; efferent lymph leaves by fewer, larger vessels than enter. - **B-cell real estate:** cortical follicles; secondary follicles show a dark zone of centroblasts, a light zone of centrocytes, a mantle zone rim and tingible body macrophages — the anatomy of antibody affinity maturation. - **T-cell real estate:** paracortex (inner cortex) with high endothelial venules, the portal by which lymphocytes migrate from blood into the node; paracortical hyperplasia marks viral infections and drug reactions. - **Medulla:** medullary cords rich in plasma cells and B cells between medullary sinuses lined by histiocytes — plasma cells here are the endpoint of the B-cell journey. - **Reticular framework:** reticular fibres and fibroblastic reticular cells conduct lymph and support immune-cell traffic; capsule and trabeculae give the node its shape. - **Tuberculous lymphadenitis:** caseating granulomas with epithelioid cells, Langhans giant cells and rim of lymphocytes — cervical nodes most often, the commonest cause of chronic lymphadenopathy in India. - **Sinus histiocytosis:** distended sinuses packed with macrophages, classically in nodes draining breast carcinoma and associated with a better prognosis. - **Clinical anchors:** hard, fixed, matted nodes suggest malignancy; tender mobile nodes suggest infection; axillary node status still stages breast cancer. ## Interpreting an enlarged node from the pattern outward Histology converts a swollen neck node into a diagnosis by reading which compartment has reacted. Preserved architecture with large germinal centres full of tingible body macrophages points to reactive follicular hyperplasia — the picture in chronic non-specific lymphadenitis or human immunodeficiency virus infection early on. If the paracortex expands instead, with immunoblasts and prominent high endothelial venules, think viral lymphadenitis or a drug hypersensitivity such as phenytoin. When the architecture is replaced by islands of epithelioid macrophages with Langhans giant cells around central caseous necrosis, the diagnosis is tuberculosis until proven otherwise — and in Indian practice fine-needle aspiration cytology of a cervical node reporting caseating granulomatous lymphadenitis typically leads to antitubercular therapy. Malignant patterns rewrite the map more radically. A monomorphous population effacing follicles signals lymphoma — follicular lymphoma even reproduces neoplastic follicles, which must be distinguished from reactive ones by their uniformity and loss of mantle zones. Metastatic carcinoma appears as desmoplastic deposits of epithelial cells first in the subcapsular sinus, because that is where afferent lymph first lands — a detail examiners relish, since it links flow dynamics to tumour spread. ## Where students slip The persistent error is mixing up the vessels: multiple afferent lymphatics pierce the convex capsule, while a single (or few) efferent channel and the blood vessels use the hilum — reverse this and the whole flow logic collapses. The second confusion is between the paracortex and the medulla as the T-cell and B-cell-plasma-cell zones respectively; anchor it with the high endothelial venule, which belongs to the paracortex and explains why T-cell zones swell in viral infections and why human immunodeficiency virus, which homes to these very cells, causes generalised lymphadenopathy. Finally, candidates describe germinal centres as present all the time: they exist only in activated secondary follicles, their tingible body macrophages proving active cell death and selection inside. ## Frequently asked questions ### What is the route of lymph flow through a lymph node? Afferent vessels to subcapsular sinus, then trabecular and medullary sinuses, leaving via efferent vessels at the hilum — a single direction of flow with no valves needed on the afferent side. ### Which structures characterise the paracortex? T lymphocytes and high endothelial venules, the specialised vessels through which recirculating lymphocytes enter the node from the bloodstream. ### What does a germinal centre contain? Centroblasts in the dark zone, centrocytes in the light zone, follicular dendritic cells and tingible body macrophages — the machinery of B-cell proliferation and selection. ### Which histology defines tuberculous lymphadenitis? Caseating granulomas with epithelioid macrophages, Langhans giant cells and lymphocytic rim, often with acid-fast bacilli demonstrated on Ziehl-Neelsen staining. ### Where do metastatic carcinoma cells first deposit in a node? In the subcapsular (marginal) sinus, the first chamber afferent lymph enters — the reason sinuses appear distended with malignant cells in involved nodes.