A granuloma is a specialized collection of immune cells. Granulomas are commonly seen during certain kinds of infections such as tuberculosis. Pathologists use the word granulomatous to describe the microscopic look of granulomas inside tissue.
The immune system is made up of different kinds of cells that work together to protect the body and help it heal after an injury. The immune cells at the center of the granuloma are called histiocytes and they often join together to form giant cells that contain multiple nuclei. Some granulomas have an outer layer of lymphocytes, another specialized by of immune cell that work together with the histiocytes.
Granulomas often appear in response to long standing bacterial or fungal infections and they are classically seen in 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 as necrotizing and non-necrotizing granulomas based on how they look when viewed under the microscope. Necrosis is a type of cell death and necrotizing granulomas contain dead cells at their centre. In contrast, non-necrotizing granulomas are made up entirely of immune cells.
Necrotizing granulomas are more likely to be related to infections and your pathologist may order additional special tests such as a silver stain or acid fast stain to look for infectious organisms.