Histiocytic granuloma formed in response to fibrinoid swelling and necrosis of perivascular connective tissue. Histiocytes phagocytize fibrinoid material, forming microscopic giant cells; end stage is connective tissue scar with fibroblasts and collagen deposition that is susceptible to formation of additional Aschoff nodules and scarring. Condition occurs esp. in heart and sometimes in rheumatic fever joints.