Reactive lymphadenitis: the patterns
- Lesion
Lymph nodes swell when they fight. Which part of the node grows tells which arm of immunity is working, and helps rule out lymphoma.
What it is
Lymph nodes enlarge during infection and immune stimulation. Acute nonspecific lymphadenitis is a tender, swollen node draining an infection, sometimes forming an abscess. Chronic reactive enlargement shows patterns that mirror the immune response: B-cell follicles grow in antibody responses, the T-cell paracortex grows in viral and drug reactions, and the sinuses fill with histiocytes when the node drains a tumour or debris. Granulomas point to mycobacteria, fungi, cat-scratch disease or sarcoidosis.
Structure
- Acute lymphadenitis: enlarged, red, soft node; neutrophils around follicles and in sinuses; central necrosis when pyogenic bacteria form an abscess.
- Follicular hyperplasia: many large germinal centres with a polarized mix of centroblasts and centrocytes, mitoses and tingible-body macrophages.
- Paracortical hyperplasia: expanded T-cell zones with immunoblasts that may push follicles aside.
- Sinus histiocytosis: distended sinuses packed with large histiocytes and hypertrophic lining cells.
Step by step
- Antigen or microbes drain to the node through afferent lymphatics.
- Antigen-presenting cells activate the lymphocytes of the matching compartment.
- That compartment expands: follicles for antibody responses, paracortex for T-cell responses, sinuses for clearance of particles.
- Pyogenic bacteria add neutrophils, necrosis and pus; persistent antigens favour granulomas.
- When the stimulus ends, the node shrinks, sometimes leaving fibrosis.
Patterns of reactive lymph node enlargement
| Pattern | Compartment that expands | Typical causes | Key microscopic clue |
|---|---|---|---|
| Acute nonspecific lymphadenitis | Whole node, neutrophils | Dental, skin or throat infection draining to the node | Neutrophils, oedema, sometimes abscess |
| Follicular hyperplasia | B-cell follicles | Rheumatoid arthritis, early HIV, syphilis, nonspecific stimulation | Large, irregular germinal centres with tingible-body macrophages |
| Paracortical hyperplasia | T-cell paracortex | Infectious mononucleosis and other viruses, vaccines, drugs | Immunoblasts filling the interfollicular zone |
| Toxoplasma lymphadenitis | Follicles plus small epithelioid clusters | Toxoplasma gondii | Follicular hyperplasia with epithelioid histiocytes near the follicles |
| Suppurative granulomatous lymphadenitis | Granulomas with central neutrophils | Cat-scratch disease (Bartonella henselae) | Stellate necrotizing granulomas |
| HIV lymphadenopathy | Follicles, then their collapse | Untreated HIV infection | Florid follicles early, burnt-out depleted follicles late |
Clinical notes
- Tender, warm nodes suggest acute infection; hard, fixed, painless nodes suggest cancer.
- Persistent generalized lymphadenopathy is common in HIV; in Colombia tuberculosis and histoplasmosis are frequent granulomatous causes.
- Chronic lymphadenitis is common in inguinal and axillary nodes, which drain frequent minor skin injuries.
In the lab
- Excisional biopsy keeps the architecture, which matters more than single cells in separating reactive from malignant nodes.
- Immunostaining for BCL2 and clonality studies help when follicles look suspicious.
Test yourself
Think of the answer, then tap the question to see it.
Which node compartment expands in infectious mononucleosis?
The T-cell paracortex, filled with activated immunoblasts.
Which three features favour reactive follicular hyperplasia over follicular lymphoma?
Preserved architecture, follicles of varying size and shape with tingible-body macrophages and mitoses, and BCL2-negative germinal centres.
What kind of granuloma does cat-scratch disease produce?
Stellate necrotizing granulomas with central neutrophils (suppurative granulomatous lymphadenitis).
Elsewhere in DurgiPedia
- Lymph node and spleen under the microscope
- Lymph node: cortex, paracortex, medulla
- B-cell activation, class switching and affinity maturation
- Primary and secondary lymphoid organs
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Lymphadenitis: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026); Lymphadenopathy (StatPearls (NCBI Bookshelf), 2026).
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Representative model, for educational purposes only.