Granuloma is an organized collection of macrophages that forms in response to chronic inflammation. This occurs when the immune system attempts to isolate foreign substances, including infectious organisms like bacteria and fungi, as well as other materials such as foreign objects, keratin, and suture fragments. The macrophages within granulomas often fuse together to form multinucleated giant cells. These macrophages, commonly referred to as "epithelioid," exhibit distinct features such as elongated nuclei resembling the sole of a slipper or shoe. Their cytoplasm typically appears pink when stained with eosin. The term "granuloma" is most accurately used when a pathologist examines surgically removed and specially stained tissue under a microscope to confirm the presence of these organized collections of macrophages. Granulomas are characterized by their tight, ball-like formation, with the individual cells tightly clustered. The additional cells and matrix found in granulomas may provide clues to the underlying cause of the inflammation.

Medical History: The concept of "granuloma" was first introduced in 1861 to describe small nodular aggregations of inflammatory cells. These nodules were often observed in chronic inflammatory responses triggered by various infectious and non-infectious agents. The discovery and understanding of granulomas have been significant in comprehending the body's immune response to different stimuli and pathogens.