Which of the following is not characteristic of a granuloma?
Mixture of chronic inflammatory cells
Polymorphnuclear leucocytes, cellular debris and fibrin
These are typical components of an abscess cavity. Polymorphonuclear leucocytes may be found in a granuloma if there is a focus of suppuration.
Chronic inflammation may occur secondary to acute inflammation. In most cases chronic inflammation occurs as a primary process. These may be broadly viewed as being one of three main processes:
- Persisting infection with certain organisms such as Mycobacterium tuberculosis which results in delayed type hypersensitivity reactions and inflammation.
- Prolonged exposure to non-biodegradable substances such as silica or suture materials which may induce an inflammatory response.
- Autoimmune conditions involving antibodies formed against host antigens.
Acute vs. Chronic inflammation
Changes to existing vascular structure and increased permeability of endothelial cells
Infiltration of neutrophils
Macrophages, plasma cells and lymphocytes predominate
Process may resolve with:
Healing by fibrosis is the main result
A granuloma consists of a microscopic aggregation of macrophages (with epithelial type arrangement =epitheliod). Large giant cells may be found at the periphery of granulomas.
Growth factors released by activated macrophages include agents such as interferon and fibroblast growth factor (plus many more). Some of these such as interferons may have systemic features resulting in systemic symptoms and signs, which may be present in individuals with long standing chronic inflammation.
The finding of granulomas is pathognomonic of chronic inflammation, as illustrated in this biopsy from a patient with colonic Crohns disease