A granuloma is a collection of immune cells and a type of chronic inflammation. Granulomas are made up of specialized immune cells including lymphocytes, histiocytes, and multi-nucleated giant cells. Pathologists use the word granulomatous to describe the microscopic look of granulomas inside tissue.
Any condition that causes long-standing activation of the immune system can result in the development of a granuloma. For example, granulomas often appear in response to prolonged bacterial or fungal infections and they are very commonly seen in patients with tuberculosis. Granulomas also form around foreign material (such as sutures), tumours, and in chronic inflammatory conditions such as Crohn’s disease and sarcoidosis.
Pathologists divide granulomas into two groups, necrotizing and non-necrotizing, based on how the granulomas look when viewed under the microscope. Necrosis is a type of cell death and necrotizing granulomas contain dead cells at their center. In contrast, non-necrotizing granulomas are made up entirely of immune cells.
Necrotizing granulomas are important because they are more likely to be related to infections such as tuberculosis. As a result, your pathologist may order additional special stains such as a silver stain or acid-fast stain to look for infectious organisms.