In pathology, a granuloma is a specific form of chronic inflammation characterized by the accumulation of histiocytes, which are a type of immune cell. The histiocytes in a granuloma are described as epithelioid because they stick together like epithelial cells. Other types of immune cells commonly found in a granuloma include lymphocytes and multinucleated giant cells. Granulomas often form in response to a foreign substance or a persistent pathogen that the body’s immune system is unable to clear. They serve to “wall off” the foreign material from the rest of the body.

Why do granulomas form?

Granulomas form as a result of the immune system’s attempt to isolate substances it perceives as foreign but cannot eliminate. These substances can include:

  • Infectious agents, such as bacteria (e.g., Mycobacterium tuberculosis, which causes tuberculosis), fungi (e.g., Histoplasma, which causes histoplasmosis), and parasites.
  • Foreign bodies, such as splinters, silica, or other inert particles.
  • Cellular debris such as fragments of bone, hair, or connective tissue.

Conditions associated with granulomas

Several conditions are associated with the formation of granulomas, including:

  • Infectious diseases, such as tuberculosis, leprosy, and histoplasmosis.
  • Chronic inflammatory diseases, such as sarcoidosis and Crohn’s disease.
  • Exposure to certain substances, like beryllium (berylliosis) or talc.

Necrotizing vs. non-necrotizing granulomas

The distinction between necrotizing and non-necrotizing granulomas is important for diagnosis and understanding the underlying cause of the granuloma:

  • Necrotizing granulomas contain a central area of necrosis (dead cells). This type is often associated with chronic infections, such as tuberculosis. When examined without a microscope, these granulomas are often described as caseating because they have a cheese-like appearance.
  • Non-necrotizing granulomas do not have this central area of necrosis. They are more characteristic of conditions like sarcoidosis or foreign body reactions, where the immune response is less destructive to the body’s own tissues.

The presence or absence of necrosis within a granuloma can provide vital clues to the underlying cause of the inflammation. Necrotizing granulomas often suggest an infectious cause that may require specific antimicrobial treatment. In contrast, non-necrotizing granulomas might indicate a chronic inflammatory condition or an immune response to a non-infectious agent, guiding treatment toward managing inflammation and modulating the immune system. The distinction helps pathologists and clinicians tailor the diagnostic evaluation and treatment plan for the affected individual.

About this article

Doctors wrote this article to help you read and understand your pathology report. Contact us if you have questions about this article or your pathology report. For a complete introduction to your pathology report, read this article.

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