Granulomatous inflammations are chronic processes, histologically characterized by aggregations of (often modified) histiocytes. Classification varies, e. g.:

• palisading granulomas, where modified hisitocytes form palisading borders around areas of degenerated colagen: granuloma annulare, necrobiosis lipoidica, rheumatoid nodule and others
• epithelioid granulomas, often with presence of multinuclear giant cells; in some processes (tuberculosis) necrosis: tuberculosis, rosacea, sarcoidosis, skin form of Crohn's disease, leprosy, elastolytic granuloma, berylium and zirkonium granulomas, silica granuloma, foreign body granulomas and other diseases
• inflammatory granulomas, where histiocytes are mixtured with neutrophils: deep mycosis, atypical mycobacteriosis, cat scratch disease and others.
• some foliculitis, vasculitis, fat inflammations and necrosis or even tumors have granulomatous features as well

Pyogenic granuloma is benign tumor of blood vessels with variable admixture of inflammatory infiltrate, which is usually not granulomatous (no modified histiocytes are present). This lesion is described in the chapter describing tumours of blood vessels.