Xanthomatosis: A condition in which fatty deposits occur in various parts of the body. These fatty deposits are called xanthomas or xanthomata and appear as yellowish firm nodules in the skin. Xanthomas are in themselves a harmless growth of tissue. However, they frequently indicate the presence of underlying diseases such as diabetes and disorders of fats (lipid disorder or hyperlipidemia).
Under the microscope, a xanthoma consists of lipid-laden foam cells. These cells, termed histiocytes, contain lipid material in their cytoplasm (the nonnuclear zone of the cell).