Granuloma

A granuloma is a structure formed during inflammation that is found in many diseases. It is a collection of immune cells known as macrophages. Granulomas form when the immune system attempts to wall off substances it perceives as foreign but is unable to eliminate. Such substances include infectious organisms including bacteria and fungi, as well as other materials such as foreign objects, keratin and suture fragments.Granuloma without necrosis in a lymph node of a person with sarcoidosis.Granuloma with central necrosis in a lung of a person with tuberculosis. Note the Langhans-type giant cells (with many nuclei arranged in a horseshoe-like pattern at the edge of the cell) around the periphery of the granuloma. Langhans-type giant cells are seen in many types of granulomas, and are not specific for tuberculosis. A granuloma is a structure formed during inflammation that is found in many diseases. It is a collection of immune cells known as macrophages. Granulomas form when the immune system attempts to wall off substances it perceives as foreign but is unable to eliminate. Such substances include infectious organisms including bacteria and fungi, as well as other materials such as foreign objects, keratin and suture fragments. In pathology, a granuloma is an organized collection of macrophages. In medical practice, doctors occasionally use the term 'granuloma' in its more literal meaning: 'a small nodule'. Since a small nodule can represent anything from a harmless nevus to a malignant tumor, this usage of the term is not very specific. Examples of this use of the term granuloma are the lesions known as vocal cord granuloma (known as contact granuloma), pyogenic granuloma and intubation granuloma, all of which are examples of granulation tissue, not granulomas. 'Pulmonary hyalinizing granuloma' is a lesion characterized by keloid-like fibrosis in the lung, and is not granulomatous. Similarly, radiologists often use the term granuloma when they see a calcified nodule on X-ray or CT scan of the chest. They make this assumption since granulomas usually contain calcium, although the cells that form a granuloma are too tiny to be seen by a radiologist. The most accurate use of the term 'granuloma' requires a pathologist to examine surgically removed and specially colored (stained) tissue under a microscope. Histiocytes (specifically macrophages) are the cells that define a granuloma. They often, but not invariably, fuse to form multinucleated giant cells (Langhans giant cell). The macrophages in granulomas are often referred to as 'epithelioid'. This term refers to the vague resemblance of these macrophages to epithelial cells. Epithelioid macrophages differ from ordinary macrophages in that they have elongated nuclei that often resemble the sole of a slipper or shoe. They also have larger nuclei than ordinary macrophages and their cytoplasm is typically more pink when stained with eosin. These changes are thought to be a consequence of 'activation' of the macrophage by the offending antigen.