What is the definition of a granuloma?

A granuloma is defined as a microscopic aggregation of macrophages that have transformed into epithelioid cells, typically surrounded by a rim of lymphocytes and occasionally containing multinucleated giant cells. This formation occurs as a localized inflammatory response to a variety of insults, such as persistent infections, foreign bodies, or autoimmune conditions.

In this context, the presence of macrophages indicates that the body is attempting to isolate and contain a substance it deems harmful, leading to the chronic inflammation often seen in granulomatous diseases. The epithelioid arrangement of the macrophages is characteristic of granulomas and is key in distinguishing them from other inflammatory processes.

The other options do not accurately capture the essential features that define a granuloma. For example, a mass of necrotic tissue with inflammation describes necrosis, which involves tissue death rather than the organized structure of a granuloma. A type of tumor formed by excessive tissue growth does not reflect the inflammatory nature of granulomas. Similarly, categorizing a granuloma as a specific type of infection overlooks that granulomas can arise from non-infectious processes as well, highlighting their broader significance in pathological states.