What is the definition of a granuloma?

A granuloma is defined as a microscopic aggregation of macrophages that transform into epithelioid cells, often surrounded by a rim of lymphocytes and sometimes fibroblasts. This process occurs in response to chronic inflammation, allowing the immune system to contain and isolate pathogens, foreign substances, or irritants that the body cannot eliminate. Granulomas often form in conditions such as tuberculosis, sarcoidosis, and Crohn's disease as a defensive mechanism.

The presence of epithelioid macrophages is characteristic, as they resemble epithelial cells and are crucial in forming the organized structure of a granuloma. This organization contributes to the granuloma's function in chronic inflammatory processes, where it helps to prevent the spread of the offending agent.

Other options do not accurately describe the nature of a granuloma. For instance, a mass of necrotic tissue with inflammation refers to a different pathological process, and while tumors may involve tissue growth, they are not specific to the immune response mechanisms that characterize granulomas. Lastly, granulomas are not strictly a type of infection; they can form in response to various insults, including non-infectious agents. Hence, the definition describing a microscopic aggregation of macrophages with an epithelioid arrangement aligns precisely with