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PH-IM16

Lymphadenitis: reactive and infected lymph nodes

How a node filtering infected lymph swells, why bacteria in the node make it tender and can form an abscess, which reactive and granulomatous patterns point to the cause, and how a reactive node is told apart from lymphoma.

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  • 5 steps · 9 questions
  • 3D normal anatomy

By the end, you can

  • Explain how lymph flows through a node and where B cells, T cells and sinus macrophages meet what it carries.
  • Explain how bacteria in a node cause a tender, red swelling and how it can become an abscess.
  • Relate follicular hyperplasia, paracortical hyperplasia and sinus histiocytosis to the stimuli that cause them.
  • Distinguish the granulomatous lymphadenitis of tuberculosis, nontuberculous mycobacteria, cat-scratch disease, toxoplasmosis and sarcoidosis by their pattern.
  • Recognise the features, tests and microscopic findings that separate a reactive node from lymphoma, and explain how treatment acts on the cause rather than the node.

What it is

Lymphadenitis is inflammation of a lymph node, usually in response to microbes or antigens arriving in the lymph from the region it drains; lymphadenopathy means an enlarged or abnormal node of any cause. In acute (suppurative) lymphadenitis bacteria infect the node itself, which becomes tender and may form an abscess. In reactive hyperplasia the node enlarges because its own B cells, T cells or sinus macrophages multiply in an immune response. Granulomatous lymphadenitis is a chronic pattern with granulomas, as in tuberculosis, cat-scratch disease and sarcoidosis.

4 types to tell apart
Acute suppurative lymphadenitis
Bacteria, usually staphylococci or streptococci, multiply in the node; neutrophils and pus; tender, warm and red.
Reactive hyperplasia
An immune response enlarges the follicles (B cells), the paracortex (T cells) or the sinuses (macrophages); no organism in the node.
Granulomatous lymphadenitis
Necrotising (tuberculosis, cat-scratch disease) or non-necrotising (sarcoidosis, toxoplasmosis) granulomas from an agent or antigen that persists.
Localised and generalised
One region points to a local cause in the area it drains; two or more separate regions point to a disease of the whole body.

US spelling: centre → center.

Normal function

A filter where lymph meets lymphocytes

Lymph from each region of the body passes through a chain of lymph nodes before it reaches the blood. It enters a node through several , spreads under the capsule in the and trickles through the sinuses of the cortex and to the at the hilum. Macrophages lining the sinuses catch microbes, debris and cancer cells as the lymph passes.

Each kind of immune cell waits where it can respond. B cells gather in in the outer cortex; when one meets its antigen with T-cell help, a germinal centre forms (the lymphoma lessons trace these B-cell stages). T cells and antigen-carrying dendritic cells fill the , where lymphocytes from the blood enter through high endothelial venules, and plasma cells in the release antibody into the outgoing lymph.

A healthy node is soft, bean-shaped and usually less than 1 cm across; a few small nodes can be felt in the neck, armpits and groin of healthy people. Because each node drains a defined territory, a swollen node points back to its catchment: the tonsils and teeth to the upper neck, the hand and arm to the armpit, the leg and genitals to the groin.

Point to it on the model