Multinucleate Giant Cells
Multinucleate giant cells (MGC’s), frequently present in granulomas and invariably present  in bone (osteoclasts),  are polykaryons resulting from the fusion of mononuclear phagocytes under the influence of cytokines. Granulomas may or may not contain MGC’s. Some granulomas consist entirely of MGC’s whereas others may be completely devoid of giant cells.   MGC’s may be the only significant abnormal finding in bronchial and transbronchial biopsies from patients with sarcoidosis.  The MGC’s which are present  in granulomas are traditionally  classified as being either of  Langhans or foreign body types. The Langhans cell is characterized by location of the nuclei  at the periphery of the cell  in an arcuate configuration. In the foreign body type the nuclei are randomly distributed, often aggregating towards the center of the cell. Some giant cells exhibit features of both Langhans and foreign body types. The significance, if any, of the variations of MGC morphology is unknown. MGC’s retain phagocytic capability which is considered to be less than that of  their precursor monocytes/mac-  rophages.

Touton giant cells are seen in lesions with high lipid content such as xanthoma, xanthogranuloma, and fat necrosis. They are characterized by a ring of nuclei surrounding a central eosinophilic zone and surrounded by a zone of pallor extending to the periphery of the cell.

Epithelium-derived MGC’s may be prominent in certain viral infections such as measles (Warthin-Finkeldey cells), respiratory syncytial virus, herpes simplex-varicella-zoster, and parainfluenza.  Multinucleate giant cells derived from neoplastic cells may be formed in a variety of neoplasms.