Xanthomata are localised collections of lipid-laden foam cells, which are histiocytes containing cytoplasmic lipid material. They are tumour-like enlargements rather than true neoplasms. The cells contain cholesterol, both free and esterified, triglycerides, and phospholipids. With the exception of xanthelasma, lesions may be surrounded by inflammatory cells and fibrosis.
Generally, xanthomata are caused by raised levels of lipoproteins and, or, lipids.
Tendon xanthomata are diagnostic hallmarks of familial hypercholesterolaemia - the only other causes of tendon xanthomata are so very rare (phytosterolaemia and cerebrotendinous xanthomata) that the presence of raised cholesterol and tendon xanthomata is effectively diagnostic of famial hypercholesterolaemia
Localised infiltrates of lipid-containing foam cells commonly occur on the eyelid - xanthelasma.