Category:Chronic Inflammation

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Types

Granulomatous Inflammation

  • Granulomatous inflammation is usually caused by organisms of low virulence but great persistence, or by implanted foreign bodies.
  • Classically appears as a granuloma.
    • NOT a tumour, despite the suffix "-oma".
    • A circumscribed sphere of chronic inflammatory cells enveloped by poorly organised attempts at encapsulation by local connective tissue.
  • The differences between a granuloma and an abscess must be appreciated.
    • The fibrous envelope is never as well developed as that of an abscess.
    • The inner contents are never as completely fluid as in an abscess.

Structure of a Granuloma

Central core
  • The central core which contains the agent.
  • The agent may be visible with H&E staining in section, e.g.
    • Actinobacillus lignieresii
      • The cause of "Wooden tongue" in cattle.
      • Appears as a granule, with a central core of the bacterial colony surrounded by radiating eosinophilic "clubs".
        • Clubs are considered to be formed from degenerating collagen and antigen-antibody complexes.
    • Actinomyces bovis
      • The cause of "Lumpy Jaw" in cattle.
      • Forms granules containing bacteria and "clubs".
    • Fungal hyphae
    • Parasitic larvae
    • Foreign bodies
  • The agent might not be visible without being selectively stained.
Chronic Inflammatory Cells
  • Outside the core is a substantial number of chronic inflammatory cells.
    • Mainly macrophages.
      • Often appear as epithelioid cells.
    • Lymphocytes
    • Plasma cells.
  • Neutrophils and necrotic remnants of cells can be quite prominent in the granulomas of Actinobacillus and Actinomyces species.
  • Eosinophils are prominent in parasitic granulomas.
  • A scattered and variable number of Giant cells are often seen, but not always in every granuloma.


Outer Envelope
  • The final layer is an outer envelope of incomplete fibrous tissue.
  • Giant cells can also be seen in this area.

Gross Appearance of Granulomas

  • The cut surface of granulomas varies considerably;
    • Tuberculous granulomas tend to have solid whitish cores which are often calcified.
      • Grate on the knife when cut through.
    • Parasitic granulomas are often greenish in colour due to the substantial numbers of eosinophils.
      • Older ones are also often calcified.
    • Actinobacillus and Actinomyces species often have liquefied cores due to the necrosis and neutrophils.
      • I.e. they are purulent.
      • May discharge to the surface along sinus tracts.
      • The central core of bacteria and ‘clubs’ may appear as yellowish granules in this pus.
        • Often called "sulphur granules".

Granulation Tissue

Granulation tissue (Courtesty of BioMed Archive)
  • Is completlely different to granulomatous inflammation, despite the similarity in name!
  • Occurs on the surface of the skin where large areas of the epithelium have been lost.
  • Makes up the lining of sinus tracts discharging from deeper lesions.
  • Takes its name from the gross appearance of the small vessels which appear at the surface.
    • Look like red granules.
    • These vessels supply inflammatory cells, mainly neutrophils, to the infected surface.
  • The most frequent example in domestic animals is the formation of excessive granulation tissue on the legs of horses with poorly healing wounds.
    • "Proud flesh"
  • Ulcers and open wounds may heal by granulation.

Lymphocytic Inflammation

  • Lymphocytic inflammation is a diffuse chronic ongoing inflammation.
  • Seen in:
    1. Diseases of the central nervous system.
      • Lymphocytes appear microscopically as several layers of cells around blood vessels in the perivascular space.
      • They indicate that there is damage to the nervous tissue further in.
        • Should alert to the possibility of viral infection, which is a common cause of central nervous system disease.
          • E.g. louping ill.
    2. The gut.
      • An excessive number of lymphocytes diffusely infiltrating the lamina propria, often in conjunction with plasma cells, indicate an ongoing non-specific chronic enteritis.
    3. The respiratory tract.
      • Peribronchial and peribronchiolar cuffing may occur to the point of actual lymphoid follicle formation in these areas.
        • Follicles are sometimes large enough to cause partial occlusion of the airways.
      • A feature of some chronic lung diseases.

Pages in category "Chronic Inflammation"

The following 4 pages are in this category, out of 4 total.